Patent Publication Number: US-10790419-B2

Title: LED filament and LED light bulb

Description:
TECHNICAL FIELD 
     The present disclosure relates to a lighting field, and more particularly to an LED filament and its application in an LED light bulb. 
     RELATED ART 
     Incandescent bulbs have been widely used for homes or commercial lighting for decades. However, incandescent bulbs are generally with lower efficiency in terms of energy application, and about 90% of energy input can be converted into a heat form to dissipate. In addition, because the incandescent bulb has a very limited lifespan (about 1,000 hours), it needs to be frequently replaced. These traditional incandescent bulbs are gradually replaced by other more efficient lighting devices, such as fluorescent lights, high-intensity discharge lamps, light-emitting diodes (LEDs) lights and the like. In these electric lamps, the LED light lamp attracts widespread attention in its lighting technology. The LED light lamp has the advantages of long lifespan, small in size, environmental protection and the like, therefore the application of the LED light lamp continuously grows. 
     In recent years, LED light bulbs with LED filaments have been provided on the market. At present, LED light bulbs using LED filaments as illumination sources still have the following problems to be improved. 
     Firstly, an LED hard filament is provided with a substrate (for example, a glass substrate) and a plurality of LED chips disposed on the substrate. However, the illumination appearance of the LED light bulbs relies on multiple combinations of the LED hard filaments to produce the better illumination appearances. The illumination appearance of the single LED hard filament cannot meet the general needs in the market. A traditional incandescent light bulb is provided with a tungsten filament, the uniform light emitting can be generated due to the natural bendable property of the tungsten filament. In contrast, the LED hard filament is difficult to achieve such uniform illumination appearances. There are many reasons why LED hard filaments are difficult to achieve the uniform illumination appearance. In addition to the aforementioned lower bendable property, one of the reasons is that the substrate blocks the light emitted by the LED chip, and furthermore the light generated by the LED chip is displayed similar to a point light source which causes the light showing concentrated illumination and with poor illumination uniformity. In other words, a uniform distribution of the light emitted from LED chip produces a uniform illumination appearance of the LED filament. On the other hand, the light ray distribution similar to a point light source may results in uneven and concentrated illumination. 
     Secondly, there is one kind of LED soft filament, which is similar to the structure of the above-mentioned LED hard filament and is employed a flexible printed circuit substrate (hereinafter referred to FPC) instead of the glass substrate to enable the LED filament having a certain degree of bending. However, by utilizing the LED soft filament made of the FPC, the FPC has a thermal expansion coefficient different from that of the silicon gel coated covering the LED soft filament, and the long-term use causes the displacement or even degumming of the LED chips. Moreover, the FPC may not beneficial to flexible adjustment of the process conditions and the like. Besides, during bending the LED soft filament it has a challenge in the stability of the metal wire bonded between LED chips. When the arrangement of the LED chips in the LED soft filament is dense, if the adjacent LED chips are connected by means of metal wire bonding, it is easy to cause the stress to be concentrated on a specific part of the LED soft filament when the LED soft filament is bent, thereby the metal wire bonding between the LED chips are damaged and even broken. 
     In addition, the LED filament is generally disposed inside the LED light bulb, and in order to present the aesthetic appearance and also to make the illumination of the LED filament more uniform and widespread, the LED filament is bent to exhibit a plurality of curves. Since the LED chips are arranged in the LED filaments, and the LED chips are relatively hard objects, it is difficult for the LED filaments to be bent into a desired shape. Moreover, the LED filament is also prone to cracks due to stress concentration during bending. 
     In order to increase the aesthetic appearance and make the illumination appearance more uniform, an LED light bulb has a plurality of LED filaments, which are disposed with different placement or angles. However, since the plurality of LED filaments need to be installed in a single LED light bulb, and these LED filaments need to be fixed individually, the assembly process will be more complicated and the production cost will be increased. 
     In addition, since the driving requirements for lighting the LED filament are substantially different from for lighting the conventional tungsten filament lamp. Therefore, for LED light bulbs, how to design a power supply circuitry with a stable current to reduce the ripple phenomenon of the LED filament in an acceptable level so that the user does not feel the flicker is one of the design considerations. Besides, under the space constraints and the premises of achieving the required light efficiency and the driving requirements, how to design a power supply circuitry with the structure simply enough to embed into the space of the lamp head is also a focus of attention. 
     Patent No. CN202252991U discloses the light lamp employing with a flexible PCB board instead of the aluminum heat dissipation component to improve heat dissipation. Wherein, the phosphor is coated on the upper and lower sides of the LED chip or on the periphery thereof, and the LED chip is fixed on the flexible PCB board and sealed by an insulating adhesive. The insulating adhesive is epoxy resin, and the electrodes of the LED chip are connected to the circuitry on the flexible PCB board by gold wires. The flexible PCB board is transparent or translucent, and the flexible PCB board is made by printing the circuitry on a polyimide or polyester film substrate. Patent No. CN105161608A discloses an LED filament light-emitting strip and a preparation method thereof. Wherein the LED chips are disposed without overlapped, and the light-emitting surfaces of the LED chips are correspondingly arranged, so that the light emitting uniformity and heat dissipation is improved accordingly. Patent No. CN103939758A discloses that a transparent and thermally conductive heat dissipation layer is formed between the interface of the carrier and the LED chip for heat exchange with the LED chip. According to the aforementioned patents, which respectively use a PCB board, adjust the chips arrangement or form a heat dissipation layer, the heat dissipation of the filament of the lamp can be improved to a certain extent correspondingly; however, the heat is easy to accumulate due to the low efficiency in heat dissipation. The last one, Publication No. CN204289439U discloses an LED filament with omni-directional light comprising a substrate mixed with phosphors, at least one electrode disposed on the substrate, at least one LED chip mounted on the substrate, and the encapsulant coated on the LED chip. The substrate formed by the silicone resin contained with phosphors eliminates the cost of glass or sapphire as a substrate, and the LED filament equipping with this kind of substrate avoids the influence of glass or sapphire on the light emitting of the LED chip. The 360-degree light emitting is realized, and the illumination uniformity and the light efficiency are greatly improved. However, due to the fact that the substrate is formed by silicon resin, the defect of poor heat resistance is a disadvantage. 
     SUMMARY 
     It is noted that the present disclosure includes one or more inventive solutions currently claimed or not claimed, and in order to avoid confusion between the illustration of these embodiments in the specification, a number of possible inventive aspects herein may be collectively referred to “present/the invention.” 
     A number of embodiments are described herein with respect to “the invention.” However, the word “the invention” is used merely to describe certain embodiments disclosed in this specification, whether or not in the claims, is not a complete description of all possible embodiments. Some embodiments of various features or aspects described below as “the invention” may be combined in various ways to form an LED light bulb or a portion thereof. 
     It is an object of the claimed invention to provide an LED filament, the LED filament comprises at least one LED chip, at least one pair of conductive electrodes, a first light conversion layer, a Polyimide film (hereinafter referred to PI film) and a copper foil. The copper foil and the LED chip are attached to the upper surface of the PI film, the copper foil is located between two adjacent LED chips, the conductive electrodes are disposed corresponding to the LED chip configuration. The LED chip and the copper foil, and the LED chip and the conductive electrodes are electrically connected by at least one conductive wire. The LED chip is provided with a p-junction and an n-junction, wherein the conductive wires comprise a first wire connected to the p-junction of the LED chip and a second wire connected to the n-junction of the LED chip, the first light conversion layer covers a single LED chip and part of a first wire and a second wire which are connected with the LED chip, the number of the first light conversion layers is the same as the number of the LED chips. 
     In accordance with an embodiment with the present invention, a silver plating layer is arranged on the upper surface of the copper foil, and a solder mask layer is arranged on the silver plating layer, wherein the thickness of the solder mask layer is in a range of about 30 to 50 micron (μm). 
     In accordance with an embodiment of the present invention, the first light conversion layer covers two ends of the copper foil, wherein the covering area or the average thickness of the first conversion layer disposing on each of the two ends of the copper foil are the same or not equal. The first light conversion layer covers the upper surface of the copper foil with an area ratio about 30 to 40 percent. 
     In accordance with an embodiment of the present invention, the first light conversion layer covers the copper foil, wherein the covering area or the average thickness of the first conversion layer disposing on the two ends of the copper foil and on the middle of the copper foil are the same or not equal. The first light conversion layer covering the middle surface of the copper foil has a thickness in a range of about 30 to 50 micron (μm). 
     In accordance with an embodiment of the present invention, a pair of conductive electrodes are respectively located at the ends, the head end and the tail end, of the LED filament and extending beyond the location where the copper foil on the PI film. 
     In accordance with an embodiment of the present invention, a second light conversion layer is disposed under the PI film, and the second light conversion layer is provided with an inclined surface or an inclined surface with an arc shape, wherein the upper surface of the PI film opposites to the lower surface thereof. 
     In accordance with an embodiment of the present invention, the surface of the first light conversion layer is an arc shape, and the height of the arc shape gradually decreases from the middle to the both sides with respect to the PI film, and the angle between each of the two sides of the curved shape and the PI film is an acute angle or an obtuse angle. 
     In accordance with another embodiment of the present invention, an LED filament comprises at least one LED section, a conductive section, at least two conductive electrodes and a light conversion layer. The conductive section is located between two adjacent LED sections. The two conductive electrodes are disposed on the LED filament correspondingly and electrically connected to each of the LED sections. The adjacent two LED sections are electrically connected to each other through the conductive section. Each of the LED sections includes at least two LED chips, and the LED chips are electrically connected to each other by at least one wire. The light conversion layer covers the LED sections, the conductive sections and the conductive electrodes, and a part of each of the two electrodes is exposed respectively. 
     In accordance with an embodiment of the present invention, the conductive section includes a conductor connecting with the LED section, and the length of the wire connecting between the LED chips is less than the length of the conductor. 
     In accordance with an embodiment of the present invention, the light conversion layer includes at least one top layer and one base layer. 
     In accordance with another embodiment of the present invention, an LED filament comprises at least one LED section, a conductive section, at least two conductive electrodes and a light conversion layer. The conductive section is located between two adjacent LED sections. The two conductive electrodes are electrically connected to the LED sections. The adjacent two LED sections are electrically connected to each other through the conductive section. Each of the conductive sections is electrically connected to the LED section by at least one wire. 
     In accordance with an embodiment of the present invention, each of the LED sections includes at least two LED chips, and the LED chips are electrically connected to each other by the wire. 
     In accordance with an embodiment with the present invention, the structure of the conductive section may in the form of a wavy concave, a wavy convex or a spiral shape. 
     In accordance with an embodiment with the present invention, the LED filament may include an auxiliary strip arranging in parallel with the conductive section and extending toward to the two conductive electrodes. 
     In accordance with an embodiment of the present invention, the structure of a conductor of the conductive section may in the form of wavy shaped. 
     In accordance with an embodiment of the present invention, the light conversion layer is composed of different particles corresponding to the position above the LED section and the conductive section respectively, or the light conversion layer disposed on the LED section and the conductive section are made of different materials. 
     In accordance with another embodiment of the present invention, an LED filament comprises a base layer, at least one LED chip and a top layer disposed on the base layer. The top layer having an arc-shaped concave surface is collapsed naturally from the boundary of the top layer, and the thickness of the base layer is less than or equal to the thickness of the top layer. 
     In accordance with an embodiment of the present invention, the phosphor concentration of the top layer can be greater than the phosphor concentration of the base layer. 
     In accordance with an embodiment of the present invention, the proportional relationship between the width W1 of the base layer or the top layer and the width W2 of the LED chip is W1:W2=1:0.8 to 0.9. 
     In accordance with an embodiment of the present invention, an LED filament comprises a plurality of LED chip units, a plurality of conductors, and at least two conductive electrodes. Wherein each of the conductors is located between two adjacent LED chip units, the LED chip units are disposed at different heights, and the conductive electrodes are disposed corresponding to the LED chip units configuration and electrically connected to the LED chip unit by the wire. The adjacent two LED chip units are electrically connected to each other through a conductor, and the angle between the conductor and the extending direction of length of the LED filament is in a range of about 30° to 120°. In accordance with another embodiment of the present invention provides a composition which is suitable for use as a filament substrate or a light conversion layer, wherein the composition comprises at least a main material, a modifier and an additive. The main material is an organosilicon-modified polyimide; the modifier is a thermal curing agent; and the additives comprise microparticles added into the main material, which may comprise phosphor particles, heat dispersing particles. The additive also comprises a coupling agent. 
     The present disclosure provides a composition which is suitable for use as a filament substrate or a light-conversion layer, wherein the main material in the composition is an organosilicon-modified polyimide, i.e. a polyimide comprising a siloxane moiety, wherein the organosilicon-modified polyimide comprises a repeating unit represented by general Formula (I): 
     
       
         
         
             
             
         
       
     
     In general Formula (I), Ar 1  is a tetra-valent organic group having a benzene ring or an alicyclic hydrocarbon structure, Ar 2  is a di-valent organic group, R is each independently methyl or phenyl, and n is 1˜5. 
     According to an embodiment of the present disclosure, Ar 1  is a tetra-valent organic group having a monocyclic alicyclic hydrocarbon structure or a bridged-ring alicyclic hydrocarbon structure. 
     According to another embodiment of the present disclosure, Ar 2  is a di-valent organic group having a monocyclic alicyclic hydrocarbon structure. 
     It is another object of the claimed invention to provide an LED light bulb, an LED light bulb includes a lamp housing, a lamp cap, two conductive brackets, a stem, and an LED filament. The lamp cap is electrically connected to the lamp housing, the two conductive brackets are disposed in the lamp housing, the stem extends from the lamp cap into the lamp housing, and the LED filament comprises a plurality of LED chips and two conductive electrodes. The LED chips are arranged in an array along the extending direction of the LED filaments, and the two conductive electrodes are respectively disposed at two ends of the LED filament and electrically connected to the LED chips, and the two conductive electrodes are respectively electrically connected to two conductive brackets. Wherein the LED filament is curled to satisfy symmetry characteristics in which: while a top view of the LED light bulb is presented in two dimensional coordinate system defining four quadrants with a X-axis crossing the stem, an Y-axis crossing the stem, and an origin, a brightness presented by a portion of the LED filament in the first quadrant in the top view is symmetric to a brightness presented by a portion of the LED filament in the second quadrant in the top view with respect to the Y-axis and/or is symmetric to a brightness presented by a portion of the LED filament in the third quadrant in the top view with respect to the origin; and while a side view of the LED light bulb is presented in two dimensional coordinate system defining four quadrants with a Y′-axis aligned with the stem, an X′-axis crossing the Y′-axis, and an origin, a brightness presented by a portion of the LED filament in the first quadrant in the side view is symmetric to a brightness presented by a portion of the LED filament in the second quadrant in the side view with respect to the Y′-axis. 
     In accordance with an embodiment of the present invention, an LED light bulb includes a lamp housing, a lamp caps, two conductive brackets, a stem and an LED filament. Wherein, the lamp cap is electrically connected to the lamp housing, the two conductive brackets are disposed in the lamp housing, and the stem extends from the lamp cap into the lamp housing. Moreover, the LED filament comprises a plurality of LED chips and two conductive electrodes. The LED chips are arranged in an array along the extending direction of the LED filaments, and the two conductive electrodes are respectively disposed at two ends of the LED filament and connected to the LED chips, and the two conductive electrodes are respectively connected two conductive brackets. Wherein the LED filament is curled to satisfy symmetry while a top view of the LED light bulb is presented in two dimensional coordinate system defining four quadrants with a X-axis crossing the stem, an Y-axis crossing the stem, and an origin, a structure of a portion of the LED filament in the first quadrant in the top view is symmetric to a structure of a portion of the LED filament in the second quadrant in the top view with respect to the Y-axis and/or is symmetric to a structure of a portion of the LED filament in the third quadrant in the top view with respect to the origin; and while a side view of the LED light bulb is presented in two dimensional coordinate system defining four quadrants with a Y′-axis aligned with the stem, an X′-axis crossing the Y′-axis, and an origin, a structure of a portion of the LED filament in the first quadrant in the side view is symmetric to a structure of a portion of the LED filament in the second quadrant in the side view with respect to the Y′-axis. 
     In accordance with an embodiment of the present invention, an LED light bulb includes a lamp housing, a lamp caps, two conductive brackets, stems and LED filaments. Wherein, the lamp cap is electrically connected to the lamp housing, the two conductive brackets are disposed in the lamp housing, and the stem extends from the lamp cap into the lamp housing. Moreover, the LED filament comprises a plurality of LED chips and two conductive electrodes. The LED chips are arranged in an array along the extending direction of the LED filaments, and the two conductive electrodes are respectively disposed at two ends of the LED filament and connected to the LED chips, and the two conductive electrodes are respectively connected two conductive brackets. Wherein the LED filament is curled to satisfy symmetry while a top view of the LED light bulb is presented in two dimensional coordinate system defining four quadrants with a X-axis crossing the stem, an Y-axis crossing the stem, and an origin, a length of a portion of the LED filament in the first quadrant in the top view is substantially equal to that of a portion of the LED filament in the second quadrant in the top view and/or is substantially equal to that of a portion of the LED filament in the third quadrant in the top view; and while a side view of the LED light bulb is presented in two dimensional coordinate system defining four quadrants with a Y′-axis aligned with the stem, an X′-axis crossing the Y′-axis, and an origin, a length of a portion of the LED filament in the first quadrant in the side view is substantially equal to that of a portion of the LED filament in the second quadrant in the side view. 
     In accordance with an embodiment of the present invention, a perspective diagram of the light emission spectrum of an LED light bulb is provided. The LED light bulb may be any LED light bulb disclosed in the previous embodiments, the spectral distribution of the LED light bulb is mainly between the wavelength range of about 400 nm to 800 nm. Moreover, there are three peak wavelengths P1, P2, P3 in wavelength ranges corresponding to the light emitted by the LED light bulb. The wavelength of the peak value P1 is between about 430 nm and 480 nm, the wavelength of the peak value P2 is between about 580 nm and 620 nm, and the wavelength of the peak value peak P3 is between about 680 nm and 750 nm. The light intensity of the peak P1 is less than that of the peak P2, and the light intensity of the peak P2 is less than the light intensity of the peak P3. 
     It is another object of the claimed invention to provide an LED power supply module, the power supply module is disposed in the lamp cap of an LED light bulb, and the power supply module includes a rectifying circuit, a filtering circuit, and a driving circuit. The rectifying circuit is electrically connected to the first pad and the second pad to receive an external driving signal. The first pad and the second pad are respectively connected to the first area and the second area of the lamp cap, wherein the first area and the second area are electrically isolation. The rectifying circuit is configured to rectify an external driving signal to output a rectified signal. The filtering circuit is electrically connected to the rectifying circuit for filtering the rectified signal and generating a filtered signal accordingly. The driving circuit is electrically connected to the filtering circuit and the LED light emitting part, and for performing power conversion on the filtered signal and accordingly generating a driving power source, wherein the LED light emitting part is illuminated in response to the driving power source. According to the present invention employs the above technical schemes, therefore at least one or any combination of the following beneficial effects can be achieved. 
     A copper foil and at least one LED chip are attached on the LED filament substrate, the first wire and the second wire electrically connected between each of the LED chips are separately wrapped by the first light conversion layer, which increases the thermal radiation area, improves the heat dissipation effect and the light emitting efficiency of the LED filament; 
     The bent LED filament can be emitted, also the probability of conductive wire falling off is reduced and thereby the reliability of the product is improved; 
     The LED filament structure is provided with an LED section and a conductive section, so that the stresses normally concentrated on the conductive section when the LED filament is bent, and consequently the metal wire connecting between the adjacent chips in the LED section is resulted with lower probability of breakage. Thereby the overall quality of the LED filament is improved. In addition, for the embodiment employs a copper foil as the conductive section, it reduces the length of the metal wire bonding and further reduces the probability of breakage of the metal wire in the conductive section; 
     The LED filament structure providing with various design even realizing by the Formula that can improve the overall luminous efficiency of the LED light lamp; 
     The conductor or the wire connecting the LED chip unit and the conductor has an angle with respect to the extending direction of the LED filament in the cross sectional view. In this way, when the LED filament is bent, the internal stresses forces on the sectional conductor are reduced effectively and also the breakage probability of the LED filament is reduced. Therefore, the quality of the LED filament and its application is improved; 
     Using the organosilicon-modified polyimide resin composition the filament substrate, the filament has good flexibility, so that the filament can be made into various shapes to achieve 360° omnidirectional illumination; 
     The LED light bulb includes a single LED filament, and the posture of the LED filament has a symmetrical characteristic. This symmetrical characteristic helps to produce a uniform and wide illumination distribution, so that the LED light bulb can produce an omni-directional light appearance; 
     Due to the LED filament utilizing the special spectral design differ from the traditional LED spectral distribution pattern, the LED light bulb features a close resemblance with the traditional incandescent bulb and close to the spectral distribution of natural light, thereby improve the comfort of the light on the human body; and 
     When the LED light bulb is turned on, the power supply circuitry provides a stable current to the LED filament with ripple low enough for the user without sensing of the flicker. 
     To make the above and other objects, features, and advantages of the present invention clearer and easier to understand, the following embodiments will be described in detail with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
         FIGS. 1A and 1B  are perspective views of the LED light bulb in accordance with an embodiment of the present invention; 
         FIG. 2  is a perspective view of the LED filament with partial sectional view in accordance with an embodiment of the present invention; 
         FIGS. 3A to 3F  are cross sectional views of various LED filaments in accordance with the present invention; 
         FIGS. 4A to 4F  are cross sectional views of various LED filaments in accordance with the present invention; 
         FIG. 4G  is a schematic view showing the bent state of the LED filament of  FIG. 4F  in accordance with an embodiment of the present invention; 
         FIGS. 4H to 4K  are cross sectional views of various LED filaments in accordance with the present invention; 
         FIG. 5  is a perspective view of the LED filament with partial sectional view in accordance with an embodiment of the present invention; 
         FIG. 6A  is a cross sectional view of an LED filament in accordance with an embodiment of the present invention; 
         FIGS. 6B to 6J  are cross sectional views of various LED filaments in accordance with the present invention; 
         FIGS. 6K and 6L  are perspective views of various LED filaments in accordance with the present invention; 
         FIG. 6M  illustrates a partial top view of  FIG. 6L ; 
         FIG. 7  is a cross sectional view of an LED filament with multiple layers in accordance with an embodiment of the present invention; 
         FIG. 8  is a cross sectional view of an LED filament with multiple layers in accordance with an embodiment of the present invention; 
         FIG. 9  is a cross sectional view of an LED filament with multiple layers in accordance with an embodiment of the present invention; 
         FIG. 10  is a cross sectional view of an LED filament with multiple layers in accordance with an embodiment of the present invention; 
         FIG. 11  is a cross sectional view of an LED filament with multiple layers in accordance with an embodiment of the present invention; 
         FIG. 12  is a perspective view of an LED filament with partial cutaway in accordance with an embodiment of the present invention; 
         FIG. 13  is a perspective view of an LED filament with partial cutaway in accordance with an embodiment of the present invention; 
         FIG. 14A  is a cross sectional view of an LED filament in accordance with an embodiment of the present invention; 
         FIG. 14B  is a top view of the conductor of an LED filament in accordance with an embodiment of the present invention; 
         FIG. 14C  is a top view of the conductor of an LED filament in accordance with an embodiment of the present invention; 
         FIG. 14D  is a cross sectional view of the conductor of an LED filament in accordance with an embodiment of the present invention; 
         FIGS. 14E to 14I  are bottom views of various designs of the conductor of an LED filament in accordance with the present invention; 
         FIGS. 14J to 14M  are schematic views showing an LED filament with attaching strength being enhanced in accordance with the present invention, wherein 
         FIG. 14J  is a perspective view of a conductor,  FIG. 14K  is a perspective view showing a base layer, a conductor and a top layer, and  FIGS. 14L and 14M  are cross sectional views along a line E 1 -E 2  in  FIG. 14K  for different structures; 
         FIG. 14N  is a cross sectional view of the conductor of an LED filament in accordance with an embodiment of the present invention; 
         FIG. 14O  is a schematic view showing the bent state of the LED filament of  FIG. 14A  in accordance with an embodiment of the present invention; 
         FIG. 15  is a cross sectional view of the structure of an LED filament in accordance with an embodiment of the present invention; 
         FIG. 16  is a cross sectional view of the structure of an LED filament in accordance with an embodiment of the present invention; 
         FIGS. 17A to 17D  are cross sectional views of various LED filaments in accordance with the present invention; 
         FIGS. 17E and 17F  are schematic views showing the placement of the LED chip in  FIGS. 17A and 17B ; 
         FIG. 18  is a schematic view showing the interfaces passing through by the light emitted by the LED chip in accordance with the present invention; 
         FIG. 19A  is a cross sectional view showing the LED filament in the axial direction of the LED filament; 
         FIG. 19B  is a cross-sectional view showing the LED filament in the radial direction of the LED filament; 
         FIGS. 20A and 20B  are cross sectional views showing different top layers  420   a  of the LED filament units  400   a   1 ; 
         FIG. 20C  is a cross sectional view showing another embodiment of the LED filament in accordance with the present invention; 
         FIGS. 21A to 21I  are schematic top views of a plurality of embodiments in accordance with the present invention; 
         FIG. 22A  is a schematic structural view showing an embodiment of a layered structure of an LED filament in accordance with the present invention; 
         FIG. 22B  is a schematic structural view of an LED chip bonding wire of an embodiment in accordance with the present invention; 
         FIG. 23  shows the TMA analysis of the polyimide before and after adding the thermal curing agent; 
         FIG. 24  shows the particle size distributions of the heat dispersing particles with different specifications; 
         FIG. 25A  shows the SEM image of an organosilicon-modified polyimide resin composition composite film (substrate); 
         FIG. 25B  shows the cross-sectional scheme of an organosilicon-modified polyimide resin composition composite film (substrate) according to an embodiment of the present invention; 
         FIG. 25C  shows the cross-sectional scheme of an organosilicon-modified polyimide resin composition composite film (substrate) according to another embodiment of the present disclosure; 
         FIG. 26A  illustrates a perspective view of an LED light bulb according to the third embodiment of the instant disclosure; 
         FIG. 26B  illustrates an enlarged cross-sectional view of the dashed-line circle of  FIG. 26A ; 
         FIG. 26C  is a projection of a top view of an LED filament of the LED light bulb of  FIG. 26A ; 
         FIG. 27A  is a perspective view of an LED light bulb according to an embodiment of the present invention; 
         FIG. 27B  is a front view of an LED light bulb of  FIG. 27A ; 
         FIG. 27C  is a top view of the LED light bulb of  FIG. 27A ; 
         FIG. 27D  is the LED filament shown in  FIG. 27B  presented in two dimensional coordinate system defining four quadrants; 
         FIG. 27E  is the LED filament shown in  FIG. 27C  presented in two dimensional coordinate system defining four quadrants; 
         FIGS. 28A to 28D  are respectively a perspective view, a side view, another side view and a top view of an LED light bulb in accordance with an embodiment of the present invention; 
         FIGS. 29A to 29D  are respectively a perspective view, a side view, another side view and a top view of an LED light bulb in accordance with an embodiment of the present invention; 
         FIGS. 30A to 30D  are respectively a perspective view, a side view, another side view and a top view of an LED light bulb in accordance with an embodiment of the present invention; 
         FIGS. 31A to 31D  are respectively a perspective view, a side view, another side view and a top view of an LED light bulb in accordance with an embodiment of the present invention; 
         FIGS. 32A to 32D  are respectively a perspective view, a side view, another side view and a top view of an LED light bulb in accordance with an embodiment of the present invention; 
         FIGS. 33A to 33D  are respectively a perspective view, a side view, another side view and a top view of an LED light bulb in accordance with an embodiment of the present invention; 
         FIGS. 34A to 34D  are respectively a perspective view, a side view, another side view and a top view of an LED light bulb in accordance with an embodiment of the present invention; 
         FIGS. 35A to 35D  are respectively a perspective view, a side view, another side view and a top view of an LED light bulb in accordance with an embodiment of the present invention; 
         FIG. 36  is a schematic view showing the light emission spectrum of an LED light bulb in accordance with an embodiment of the present invention; 
         FIG. 37  is a schematic view showing the light emission spectrum of an LED light bulb in accordance with another embodiment of the present invention; 
         FIGS. 38A to 38C  are schematic circuit diagrams of an LED filament in accordance with an embodiment of the present invention; 
         FIGS. 39A to 39C  are schematic circuit diagrams of an LED filament in accordance with another embodiment of the present invention; 
         FIGS. 40A to 40D  are schematic circuit diagrams of an LED filament in accordance with another embodiment of the present invention; 
         FIGS. 41A to 41E  are schematic circuit diagrams of an LED filament in accordance with another embodiment of the present invention; 
         FIG. 42  is a block diagram of a power supply module of an LED light bulb in accordance with an embodiment of the present invention; 
         FIG. 43A  is a schematic diagram of a rectifying circuit in accordance with an embodiment of the present invention; 
         FIG. 43B  is a schematic diagram of a rectifying circuit in accordance with another embodiment of the present invention; 
         FIG. 44A  is a schematic diagram of a filtering circuit in accordance with an embodiment of the present invention; 
         FIG. 44B  is a schematic diagram of a filtering circuit in accordance with another embodiment of the present invention; 
         FIG. 45  is a block diagram of a driving circuit in accordance with an embodiment of the present invention; 
         FIGS. 46A to 46D  are schematic diagrams showing signal waveforms of a driving circuit in accordance with various embodiments of the present invention; 
         FIG. 47A  is a perspective diagram of a driving circuit in accordance with an embodiment of the present invention; and 
         FIG. 47B  is a perspective diagram of a driving circuit in accordance with another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure provides a novel LED filament and its application the LED light bulb. The present disclosure will now be described in the following embodiments with reference to the drawings. The following descriptions of various implementations are presented herein for purpose of illustration and giving examples only. This invention is not intended to be exhaustive or to be limited to the precise form disclosed. These example embodiments are just that—examples—and many implementations and variations are possible that do not require the details provided herein. It should also be emphasized that the disclosure provides details of alternative examples, but such listing of alternatives is not exhaustive. Furthermore, any consistency of detail between various examples should not be interpreted as requiring such detail—it is impracticable to list every possible variation for every feature described herein. The language of the claims should be referenced in determining the requirements of the invention. 
     In the drawings, the size and relative sizes of components may be exaggerated for clarity. Like numbers refer to like elements throughout. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items and may be abbreviated as “/”. 
     It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers, or steps, these elements, components, regions, layers, and/or steps should not be limited by these terms. Unless the context indicates otherwise, these terms are only used to distinguish one element, component, region, layer, or step from another element, component, region, or step, for example as a naming convention. Thus, a first element, component, region, layer, or step discussed below in one section of the specification could be termed a second element, component, region, layer, or step in another section of the specification or in the claims without departing from the teachings of the present invention. In addition, in certain cases, even if a term is not described using “first,” “second,” etc., in the specification, it may still be referred to as “first” or “second” in a claim in order to distinguish different claimed elements from each other. 
     It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. 
     It will be understood that when an element is referred to as being “connected” or “coupled” to or “on” another element, it can be directly connected or coupled to or on the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled,” or “immediately connected” or “immediately coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). However, the term “contact,” as used herein refers to a direct connection (i.e., touching) unless the context indicates otherwise. 
     Embodiments described herein will be described referring to plan views and/or cross-sectional views by way of ideal schematic views. Accordingly, the exemplary views may be modified depending on manufacturing technologies and/or tolerances. Therefore, the disclosed embodiments are not limited to those shown in the views, but include modifications in configuration formed on the basis of manufacturing processes. Therefore, regions exemplified in figures may have schematic properties, and shapes of regions shown in figures may exemplify specific shapes of regions of elements to which aspects of the invention are not limited. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element&#39;s or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     Terms such as “same,” “equal,” “planar,” or “coplanar,” as used herein when referring to orientation, layout, location, position, shapes, sizes, amounts, or other measures do not necessarily mean an exactly identical orientation, layout, location, position, shape, size, amount, or other measure, but are intended to encompass nearly identical orientation, layout, location, position, shapes, sizes, amounts, or other measures within acceptable variations that may occur, for example, due to manufacturing processes. The term “substantially” may be used herein to emphasize this meaning, unless the context or other statements indicate otherwise. For example, items described as “substantially the same,” “substantially equal,” or “substantially planar,” may be exactly the same, equal, or planar, or may be the same, equal, or planar within acceptable variations that may occur, for example, due to manufacturing processes. 
     Terms such as “about” or “approximately” may reflect sizes, orientations, or layouts that vary only in a small relative manner, and/or in a way that does not significantly alter the operation, functionality, or structure of certain elements. For example, a range from “about 0.1 to about 1” may encompass a range such as a 0%-5% deviation around 0.1 and a 0% to 5% deviation around 1, especially if such deviation maintains the same effect as the listed range. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present application, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Referring to  FIGS. 1A and 1B ,  FIG. 1A  and  FIG. 1B  are schematic structural diagrams showing the structure of a first embodiment and a second embodiment of the present invention. As shown in the figures, the LED light bulbs  1   a ,  1   b  include a lamp housing  12 , a lamp cap  16  connected with the lamp housing  12 , at least two conductive brackets (also referring to conductive supports)  51   a ,  51   b  disposed in the lamp housing  12 , a driving circuit  518  disposed in the lamp cap  16  and electrically connected to the conductive brackets  51   a .  51   b  and the lamp cap  16 , and a single strip light emitting part  100  disposed in the lamp housing  12 , the embodiment of the light emitting part  100  may be an LED filament including an LED chip. 
     The conductive brackets  51   a  and  51   b  are used for electrically connecting with the two conductive electrodes  506  of the LED filament  100 , and can also be used for supporting the weight of the LED filament  100 . The driving circuit  518  is electrically connected to the conductive brackets  51   a ,  51   b  and the lamp cap  16 . The lamp cap  16  is configured to connect to the lamp socket of the conventional light bulb. The lamp socket is used to transmit the electricity to the lamp cap  16 . The driving circuit  518  is used to drive the light emitting part  100  emitting the light ray after the driving circuit  518  obtains the electricity from the lamp cap  16 . The LED light bulbs  1   a  and  1   b  can generate omni-directional light because of the light emitting part  100  of the LED light bulbs  1   a  and  1   b  has symmetrical characteristics in terms of structure, shape, contour, curve, or the like, or the symmetrical characteristics of the light emitting direction of the light emitting part  100  (that is, the light emitting surface of the LED filament of the present invention, the details as described later). In the present embodiment, the driving circuit  518  is disposed within the LED light bulb. However, in some embodiments, the drive circuit  518  is disposed outside of the LED light bulb. 
     In the embodiment as shown in the  FIG. 1A , the conductive brackets  51   a ,  51   b  of the LED light bulb  1   a  are exemplified by two, but not limited thereto, and the number of the conductive brackets can be increased by the requirements of conducting or supporting of the light emitting part  100 . 
     In the embodiment as shown in the  FIGS. 1A and 1B , each of the LED light bulbs  1   a ,  1   b  further includes a stem  19  and a heat sink  17 . The stem  19  is disposed in the lamp housing  12 , and the heat sink  17  is located between the lamp cap  16  and the lamp housing  12  and is connected to the stem  19 . In the present embodiment, the lamp cap  16  is indirectly connected to the lamp housing  12  through the heat sink  17 . In some embodiments, the lamp cap  16  can be directly connected to the lamp housing  12  without heat sink  17 . The light emitting part  100  is connected to the stem  19  via the conductive brackets  51   a  and  51   b . The stem  19  can be used to exchange the air in the LED light bulb  1   b  and replace the air with a mixture of nitrogen and helium. The stem  19  can also provide a thermal dissipating function to transfer the heat generated by the light emitting part  100  to the outside of the lamp housing  12 . The heat sink  17  may be a hollow cylindrical body that surrounds the opening of the lamp housing  12 . The heat sink  17  is connected with the stem  19  and the lamp cap  16  and is used for conducting the heat generated there between to the outside of the LED light bulb  1   b . The inside of the heat sink  17  may be provided with a driving circuit  518 . The contour of the heat sink  17  is in contact with the air outside the lamp housing  12  to dissipate the heat. The heat sink  17  can be made of metal, ceramic or high thermal conductivity plastic with good thermal conductivity. 
     The material of the heat sink  17 , along with the opening/thread of the LED light bulb, can also be a ceramic material with good thermal conductivity. The heat sink  17  can also be integrally formed with the ceramic stem  19 . In this way, the heat sink  17  being glued with the lamp cap  16  of the LED light bulb can be eliminated. The thermal resistance of the heat dissipation path of the light emitting part  100  can be reduced, thereby the LED light bulb hays a better heat dissipation effect. 
     The  FIG. 2  is a perspective with partially cross sectional view showing an embodiment of a light emitting part of the present invention. The present invention will be described below with an LED filament as a light emitting part. However, the embodiment in which the LED filament of the LED light bulb of the present invention may be implemented is not limited thereto. And any LED filament can be bent with various shapes and therefore capable of emitting an omni-directional light that should be regarded as an equivalent replacement element for the light emitting part of the present invention. The LED filament  100  includes a plurality of LED chip units  102 ,  104 , at least two conductive electrodes  110 ,  112 , and a light conversion layer  120  (in a particular embodiment, the light conversion layer may be referred to a silicone layer). The phosphors in the light conversion layer  120  absorbs certain radiation (such as light) and emits the light. The LED filament  100  emitting light rays when the conductive electrodes  110 ,  112  are powered on (voltage source or current source). In the present embodiment, the light emitted by the LED filament can be substantially 360 degrees and similar to the illumination of the point light source. Therefore, once the LED filament of the embodiment of the present invention is applied to an LED light bulb, the illumination with omni-directional light can be achieved. 
     As shown in the  FIG. 2 , the cross sectional shape of the LED filament  100  of the present invention is rectangular, but the cross sectional shape of the LED filament  100  is not limited thereto. The cross sectional shape of the LED filament  100  may be triangular, circular, elliptical, polygonal, rhombus, or even square with the corners as chamfered or rounded. 
     The LED chip units  102 ,  104 , or named with the LED section  102 ,  104 , may be composed of a single LED chip, or two LED chips. Of course, it may also include multiple LED chips, that is, equal to or greater than three LED chips. 
       FIGS. 3A to 3F  are cross sectional views showing various embodiments of the LED filament in accordance with the present invention. As shown in  FIG. 3A , the LED filament includes the LED chip units  102 ,  104 , the conductive electrodes  110 ,  112 , and the wires. The difference between the present embodiment and the previous embodiment is the light conversion layer  120  in the present embodiment is provided with a first light conversion layer  121  and a base layer  122 . The upper surface of the base layer  122  is attached with a plurality of copper foils  116  and the LED chip units  102  and  104 . The copper foils  116  are located between two adjacent LED chip units  102 ,  104 . Wherein, the conductive electrodes  110 ,  112  are disposed corresponding to the LED chip units  102 ,  104 , and the LED chip units  102 ,  104  and the copper foil  116 , the LED chip units  102 ,  104  and the conductive electrodes  110 ,  112  are electrically connected by wires respectively. The LED chip is provided with a p-junction and an n-junction, wherein the conductive wires comprise a first wire  141  used for connecting the LED chip units  102 ,  104  with the conductive electrodes  110 ,  112 , and a second wire  142  used for connecting the LED chip units  102 ,  104  with the copper foil  116 . The first light conversion layer  121  covers a single LED chip unit and the first wire  141  and the second wire  142  connecting to the LED chip unit. The number of the first light conversion layers  121  is the same as the number of the LED chip unit. The LED light bulb employs the LED filament as aforementioned designs, the heat dissipation function and the light emitting efficiency of the LED filament are improved due to the thermal radiation area is increased. Furthermore, because the probability of the wire disconnection is reduced, the reliability of the LED light bulb product is increased, and also the brightness and illuminated appearance of the LED filament with bending curve is achieved. 
     According to present embodiment, each of the LED chip units  102 ,  104  includes two LED chips, and of course, may also include a plurality of LED chips, that is, equal to or greater than three LED chips. The exterior shape of the LED chip can be a strip type, but the present invention is not limited thereto. The strip type LED chip has fewer conductive electrodes, reducing the possibility of shielding the light emitted by the LED chip. The LED chip units  102  and  104  are connected in series and the conductive electrodes  110  and  112  are disposed at two ends of the connected LED chip units, and a portion of each of the conductive electrodes  110  and  112  is exposed outside the first light conversion layer  121 . Each of the six sides of every LED chip in the LED chip units  102 ,  104  is covered by the first light conversion layer  121 , that is, six sides of the LED chip of the LED units  102 ,  104  are covered by a first light conversion layer  121 , and covering coverage may be partial overlap or as wrap but not limited to direct contact. Preferably, in the present embodiment, each of the six sides of the LED chip of the LED chip units  102 ,  104  directly contacts the first light conversion layer  121 . However, in the implementation, the first light conversion layer  121  may cover merely one of the six sides of each of the LED chip of the LED chip units  102 ,  104 , that is, the first light conversion layer  121  directly contacts the one side such as a top or a bottom side. Similarly, the first light conversion layer  121  can directly contact at least one side of the two conductive electrodes  110 ,  112  or the copper foil  116 . 
     The wire is a gold wire or an aluminum wire, and the combination of the copper foil  116  and the gold wire to provide the LED filament having a stabilized and a flexible conductive structure. The copper foil  116  can be replaced by any other conductive material. The width or/and length of the opening of the copper foil  116  is larger than the contour of the LED chip units  102 ,  104  and further to define the positions of the LED chip units  102 ,  104 . Furthermore, at least two of the six faces of the LED chip units  102 ,  104  are contacted and covered by the first light conversion layer  121 . By utilizing the copper foil  116  and the wire as linkage, a plurality of the LED chip units  102  and  104  are interconnected in series, in parallel or in a combination of both. Then, the front end and the rear end of the interconnected LED chip units  102 ,  104  are respectively connected to the two conductive electrodes  110 ,  112  disposing on the base layer  122 , and the conductive electrodes  110 ,  112  are electrically connected to the power supply to provide the electricity for emitting the LED chip units  102 ,  104 . 
     The first light conversion layer  121  covers two ends of the copper foil  116 , wherein the covering area or the average thickness of the first conversion layer  121  disposing on each of the two ends of the copper foil  116  are substantially the same or not equal. The first light conversion layer  121  covers the upper surface of the copper foil  116  with an area ratio about 30 to 40 percent. In an embodiment of the present invention, as shown in the  FIG. 3B , the first light conversion layer  121  may cover the entire copper foil  116  disposing between the two adjacent first light conversion layers. Wherein the covering area or the average thickness of the first conversion layer  121  disposing on the two ends of the copper foil  116  and on the middle of the copper foil  116  are not equal. The first light conversion layer  121  covering the middle surface of the copper foil has a thickness in a range of about 30 to 50 micron (μm). The surface of the first light conversion layer  121  is an arc shape, and the height of the arc shape gradually decreases from the middle to the both sides with respect to the base layer  122 , and the angle between each of the two sides of the curved shape and the base layer  122  is an acute angle or an obtuse angle. 
     The first light conversion layer  121  includes a phosphor gel or a phosphor film. At least a portion of each of the six sides of the LED chip units  102 ,  104  directly contacts the first light conversion layer  121  and/or one or both sides of each of the LED chip unit  102 ,  104  are bonded to the first light conversion layer  121  through the glue. In the aforementioned embodiment, the six sides the LED chip units  102 ,  104  are all covered by the first light conversion layer  121  and/or partially direct contacted with the first light conversion layer  121 . Both embodiments have equivalent concept. In some embodiments, the foregoing glue may also incorporate with phosphors to increase the overall light conversion efficiency. The glue is usually also a silicon gel. The difference between the glue and the silicon gel is the glue generally mixed with silver powder or heat dissipating powder to improve the thermal conductivity. 
     As shown in  FIG. 3C , the difference from the aforementioned embodiment is that the lower surface of the base layer  122  is covered by a second light conversion layer  123  with a uniform thickness. The upper surface and the lower surface of the base layer  122  are opposite to each other. As shown in  FIG. 3D , the second light conversion layer  123  covering the lower surface of the base layer  122  has an inclined side or an inclined side with an arc shape. The lower surface of the base layer  122  covering by the second light conversion layer  123 , the LED filament therefore can generate fluorescence with more yellow light and less blue light. Therefore, the difference in color temperature between the front and back surfaces of the LED chip units  102  and  104  can be reduced. Thereby, the color temperature of emitting light from both sides of the LED chip units  102  and  104  is closer. 
     In one embodiment, as shown in  FIG. 3E , the first light conversion layer  121  covers two adjacent LED chip units  102 ,  104 , a copper foil  116  is located between two adjacent LED chip units  102 ,  104 , and the first wire  141  and the second wire  142  connecting between the LED chip units  102  and  104 . In one embodiment, a silver plating layer  118  is disposed on the upper surface of the copper foil  116 , and a portion of the copper foil  116  located at the ends of the LED filament and extending beyond the base layer  122  can serve as the conductive electrodes  110 ,  112 . The silver plating layer  118  not only has good electrical conductivity but also has the effect of increasing light reflection. The surface of the silver plating layer  118  can be selectively provided with a solder mask layer (not shown), and the thickness of the solder mask layer is 30˜50 um. The solder mask layer is obtained by an OSP (Organic Solderability Preservatives) process. The solder mask layer has functions of oxidation resistance, thermal shock resistance, and moisture resistance. 
     In another embodiment of the present invention, as shown in  FIG. 3F , the LED filament  200  has LED chip units  102 ,  104 , conductive electrodes  110 ,  112 , wires  140 , and a light conversion layer  120 . The copper foil  116  is located between the adjacent two LED chip units  102 ,  104 , the conductive electrodes  110 ,  112  are arranged corresponding to the LED chip units  102 ,  104 , and the LED chip units  102 ,  104  and the copper foil  116 , the LED chip units  102 ,  104  and the conductive electrodes  110 ,  112  are electrically connected by wire  140  respectively. The light conversion layer  120  is disposed on the LED chip units  102 ,  104  and at least two sides of conductive electrodes  110 ,  112 . The light conversion layer  120  exposes a portion of each of the conductive electrodes  110 ,  112  of the LED filament, and the light conversion layer  120  includes a phosphor layer  124  and a silicon layer  125 . The phosphor layer  124  directly contacts the surfaces of the LED chip unit  102 ,  104 . In the phosphors spraying process, the phosphors may be sprayed on the surfaces of the LED chip unit  102 ,  104 , the copper foil  116 , the conductive electrodes  110 ,  112  and the wire  140  by electrostatic spraying to form the phosphor layer  124 . Then, the vacuum coating method can be used to disposing a silicon layer  125  on the phosphor layer  124 , wherein the silicon layer  125  does not contain phosphor. The thickness of the phosphor layer  124  and the silicon layer  125  are equal or unequal. The thickness of the phosphor layer  124  and silicon layer  125  respectively is about 30 to 70 micron (um) and 30 to 50 micron (um). In another embodiment, the surfaces of the LED chip units  102 ,  104 , the copper foil  116 , the conductive electrodes  110 ,  112 , and the wires  140  may be covered with a transparent resin layer, and the transparent resin layer does not contain phosphors, and then covered by phosphors powder on the transparent resin layer. The thickness of the transparent resin layer and the phosphor layer are equal or unequal, and the thickness of the transparent resin layer is about 30 to 50 micron (um). 
     Referring to  FIGS. 4A to 4K ,  FIGS. 4A to 4K  are schematic views of various embodiments of an LED filament, and  FIGS. 4A to 4E  and  FIGS. 4H to 4K  are cross sectional views for different segments of the LED filament along the axial direction thereof. The  FIG. 4G  is a schematic view of the bent state of the LED filament of  FIG. 4F . As shown in  FIG. 4A  to  FIG. 4K , the LED filament can be divided into different segments in the axial direction of the LED filament, for example, the LED filament can be distinguished as an LED section  102 ,  104  (ie, the LED chip unit referred to foregoing embodiment) and the conductive section  130 , but not limited thereto. The number of the LED section  102 ,  104  and the conductive section  130  in a single LED filament may be one or multiple. The LED section  102 ,  104  and conductive section  130  are disposed along the axial direction of the LED filament. Wherein, the LED section  102 ,  104  and the conductive section  130  may have different structure with specific function respectively to achieve different effects, as detailed below. 
     As shown in  FIG. 4A , the LED filament  100  includes LED sections  102 ,  104 , a conductive section  130 , at least two conductive electrodes  110 ,  112 , and a light conversion layer  120 . The conductive section  130  is located between two LED sections  102 ,  104 . The two conductive electrodes  110 ,  112  are disposed on the LED filament correspondingly and electrically connected to each of the LED sections  102 ,  104 . The two LED sections  102  and  104  are electrically connected to each other through the conductive section  130 . In the present embodiment, the conductive section  130  includes a conductor  130   a  connecting the LED sections  102  and  104 , the length of the wire  140  being less than the length of the conductor  130   a . The spacing between any two LED chips separately disposed in two different LED sections is greater than the spacing between any two adjacent LED chips in a single LED section. In addition, in accordance with other embodiments of the present invention, each of the LED sections  102 ,  104  includes at least two LED chips  142 , and the LED chips  142  are electrically connected to each other through the wires  140 , but the present invention is not limited thereto. 
     The light conversion layer  120  covers the LED sections  102 ,  104 , the conductive section  130  and the conductive electrodes  110 , 112 , and a part of each of the two electrodes is exposed respectively. In the present embodiment, each of the six sides of the LED chip  142  of each of the LED sections  102 ,  104  is covered by the light conversion layer  120 . Once the six sides of the LED chip  142  are covered by the first light conversion layer  120  and may be referred to as a light conversion layer  120  to wrap the LED chips  142 , this kind of covering or wrapping can be considered, but not limited to, as direct contact. Preferably, in the present embodiment, each of the six sides of the LED chip  142  directly contacts the light conversion layer  120 . However, in the implementation, the light conversion layer  120  may cover merely two of the six sides of each of the LED chip  142 , that is, the light conversion layer  120  directly contacts the two sides such as a top and a bottom sides showing in the  FIG. 4 , but not limited thereto. Similarly, the light conversion layer  120  can directly contact the surfaces of the two conductive electrodes  110 ,  112 . In various embodiments, the light conversion layer  120  may employ an encapsulation without function of light converting. For example, the light conversion layer  120  of the conductive section  130  may be instead of a transparent encapsulation with excellent flexibility. 
     In some embodiments, the LED filaments  100  are disposed in the LED light bulb, and only a single LED filament is disposed in each LED light bulb to provide sufficient illumination. Moreover, for a single LED filament, in order to present the aesthetic appearance and also to achieve uniform and broad illumination, even to achieve omni-directional light, the LED filament in the LED light bulb can be bent with various curves. Since the LED filament bent with various curves accompanies diversified illumination, the light emitting direction and coverage of the LED filament can be adjusted according to the requirement of the LED light bulb. For the purpose of the LED filament easily bent to form various curved postures, and also the bending stresses of the LED filament to be considered, the conductive section  130  of the LED filament is designed preferably without the LED chip but only the conductor  130   a . The conductor  130   a  (for example, a metal wire, metal coating, or conductive strip) is easier to bend compare with the LED chip, in other words, the conductive section  130  without any LED chips will be more easily to bend compare with the LED section  102 ,  104  having the LED chip. 
     As shown in  FIG. 4B , in the present embodiment, the LED section  102 ,  104  and the conductive section  130  of the LED filament  100  have different structural features. In the embodiment, the conductive section  130  further includes a wavy recess structure  132   a  encircling disposed on the surface of the conductive section  130  and symmetrically to the axis of the LED filament  100 . In the present embodiment, the wavy recess structure  132   a  is recessed in the surface of the conductive section  130 . The plurality of wavy recess structures  132   a  are arranged space apart along the axial direction and are parallel to each other to present a continuous wavy shape. 
     In the bending state of the LED filament  100 , the conductive section  130  is sustained the most stresses. Therefore, the conductive section  130  is easier to bend and capable of enduring the extending and compressing stresses due to the wavy concave structure  132   a  of the conductive section  130 . For example, the conductive section  130  may sustain both extending and compressing stresses on opposited surfaces of the conductive section  130  in the bending state, and the wavy concave structure  132   a  may improve the stress distribution of such extension and compression. The wavy concave structure  132   a  at the extension portion becomes looser and flatter, that is, the depth difference of recessions becomes smaller and the pitch of adjacent peaks or troughs becomes larger. The wavy concave structure  132   a  at the compression portion becomes closer and concave inwardly, that is, the depth difference of the concaves becomes larger and the pitch of adjacent peaks or troughs becomes smaller. Since the wavy concave structure  132   a  can provide a tolerance to endure the stresses of extension and compression and the spaces for the recessions compressed closer, the conductive section  130  is easier to be bent. 
     As shown in  FIG. 4C , in the present embodiment, the LED sections  102 ,  104  and the conductive section  130  of the LED filament  100  have different structural features. In this embodiment, the conductive section  130  further includes a wavy convex structure  132   b  encircling disposed on the surface of the conductive section  130  and symmetrically to the axis of the LED filament  100 . In the present embodiment, the wavy convex structure  132   b  protrudes from the surface of the conductive section  130 . The plurality of wavy convex structures  132   b  are arranged space apart in the axial direction and are parallel to each other to exhibit a continuous wave shape. 
     In the bending state of the LED filament  100 , the conductive section  130  is sustained the most stresses. Therefore, the conductive section  130  is easier to bend and capable of enduring the extending and compressing stresses due to the wavy convex structures  132   b  of the conductive section  130 . For example, the conductive section  130  may sustain both extending and compressing stresses on opposed surfaces of the conductive section  130  in the bending state, and the wavy convex structure  132   b  may improve the stress distribution of such extension and compression. The wavy convex structures  132   b  at the extension portion becomes looser and flatter, that is, the height difference of protrusions becomes smaller and the pitch of adjacent peaks or troughs becomes larger. The wavy convex structure  132   b  at the compression portion becomes closer and concave inwardly, that is, the height difference of the protrusions becomes larger and the pitch of adjacent peaks or troughs becomes smaller. Since the wavy convex structure  132   b  can provide a tolerance to endure the stresses of extension and compression and the spaces for the protrusions compressed closer, the conductive section  130  is easier to be bent. 
     As shown in  FIG. 4D , in the present embodiment, both the LED sections  102 ,  104  and the conductive section  130  of the LED filament  100  have similar contour, and the LED filament further includes an auxiliary strip  132   c . The auxiliary strip  132   c  is disposed in the LED filament  100  and covered by the light conversion layer  120 . The auxiliary strip  132   c  are arranged crossing the LED sections  102 ,  104  and the conductive section  130  of the LED filament and extending along the axial direction of the LED filament. 
     When the LED filament is bent, the LED sections  102 ,  104  have a smaller degree of curvature because of the LED chip  142  inside, in contrast, the conductive section  130  have a larger degree of curvature. In the case of the LED filament enduring serious bending, the degree of curvature between the LED sections  102 ,  104  and the conductive section  130  are very different. Since the stress will be concentrated in a place where the curve changes greatly, the light conversion layer  120  between the LED sections  102 ,  104  and the conductive section  130  of the LED filament will encounter higher possibility of cracking or even breakage. The auxiliary strip  132   c  has function of absorbing the stresses and breaking up the stress concentrated in the light conversion layer  120 , thereby, the auxiliary strip  132   c  disposing in the LED filament reduces the possibility of cracking or even breakage of the light conversion layer  120  between the LED sections  102 ,  104  and the conductive section  130 . By the arrangement of the auxiliary strip  132   c , the bending endurance of the LED filament is improved. In the present embodiment, the number of the auxiliary strip  132   c  is one, in other embodiments, the auxiliary strip  132   c  may be plural and disposed at different positions of the LED filament in the radial direction. 
     As shown in  FIG. 4E , in the present embodiment, the LED sections  102 ,  104  of the LED filament  100  and the conductive section  130  are identical in appearance contour, and the LED filament further includes a plurality of auxiliary strips  132   d . The plurality of auxiliary strips  132   d  are disposed in the LED filament  100  and covered by the light conversion layer  120 . The plurality of auxiliary strips  132   d  are arranged along the axial direction of the LED filament and present a segmented arrangement. Each of the auxiliary strips  132   d  is disposed in a region corresponding to each of the conductive sections  130 , and each of the auxiliary strips  132   d  extends through the corresponding conductive section  130  and extends toward to adjacent LED sections  102 ,  104  along the axial direction of the LED filament. In the present embodiment, the auxiliary strip  132   d  does not throughout the region corresponding to the LED sections  102 ,  104 . 
     When the LED filament  100  is bent, the degree of curvature between the LED sections  102 ,  104  and the conductive section  130  are very different. The plurality of auxiliary strips  132   d  can absorb the stress caused by bending between the LED sections  102 ,  104  and the conductive section  130 , and also reduce the stress concentration on the light conversion layer  120  between the LED sections  102 ,  104  and the conductive section  130 . Therefore, the auxiliary strips  132   d  disposing in the LED filament reduces the possibility of cracking or even breakage of the light conversion layer  120  on the LED sections  102 ,  104  and the conductive section  130 . By the arrangement of the auxiliary strip  132   d , the bending endurance of the LED filament is increased, thereby improving the quality of the product. In the present embodiment, the plurality of auxiliary strips  132   d  extend in the axial direction of the LED filaments and are aligned with each other in a specific radial direction. In other embodiments, the plurality of auxiliary strips  132   d  may also be extend along the axial direction of the LED filaments but not aligned with each other in a particular radial direction, and may be dispersed at different positions in the radial direction. 
     As shown in  FIG. 4F , in the present embodiment, the LED sections  102 ,  104  and the conductive section  130  of the LED filament  100  have different structure features. In the present embodiment, the conductive section  130  further includes a spiral structure  132   e  encircling disposed on the surface of the conductive section  130  and extending along the axial direction of the LED filament  100 . In the present embodiment, the spiral structure  132   e  is a spiral structure protruding from the surface of the conductive section  130 , and the spiral structure  132   e  is extending along the axial direction of the LED filament from one end of the conductive section  130  (for example, adjacent to one end of the LED section  102 ) to the other end of the conductive section  130  (for example, adjacent to one end of another LED section  104 ). As shown in  FIG. 4F , the portion of the spiral structure  132   e  located behind the conductive section  130  is represented by a dotted line in the drawing. Overall contour appearance, the spiral structure  132   e  showing a slanted arrangement relative to the axial direction of the LED filament. In other embodiments, the spiral structure  132   e  may also be a spiral-like structure that is conversely recessed into the surface of the conductive section  130 . In other embodiments of the present invention, considering the mass productivity of the overall fabrication process of the LED filament  100 , both the LED sections  102 ,  104  and the conductive section  130  of the LED filament  100  may have the same spiral structure  132   e  on the surfaces. 
     The  FIG. 4G  is a schematic view showing the bent state of the LED filament of  FIG. 4F  in accordance with an embodiment of the present invention. As shown in  FIG. 4G , in the bending state of the LED filament  100 , since the conductive section  130  serves as a mainly bending region and thereby it is sustained with the most stresses. The conductive section  130  is easier to bend and capable of enduring the extending and compressing stresses due to the spiral structures  132   e  of the conductive section  130 . For example, as shown in  FIG. 4G , the conductive section  130  may sustain both extending and compressing stresses on opposed surfaces of the conductive section  130  in the bending region, and the spiral structure  132   e  may improve the stress distribution of such extension and compression. The spiral structure  132   e  at the extension portion becomes looser and flatter, that is, the height difference of protrusions becomes smaller and the pitch of adjacent peaks or troughs becomes larger. In contrast, the spiral structure  132   e  at the compression portion becomes closer and concave inwardly, that is, the height difference of the protrusions becomes larger and the pitch of adjacent peaks or troughs becomes smaller. Since the spiral structure  132   e  can provide a tolerance to endure the stresses of extension and compression and the spaces for the protrusions compressed closer, the conductive section  130  is easier to be bent. 
     As shown in  FIG. 4H , in the present embodiment, the LED filament  100  is substantially identical to the LED filament of  FIG. 4A , the difference is that the structure of the conductor  130   b  of the conductive section  130  in the LED filament  100  of  FIG. 4H  is in the form of wavy shaped. When the LED filament is bent, the conductive section  130  serves as a mainly bending region, and the conductor  130   b  located inside the conductive section  130  is also bent along with the bending of the conductive section  130 . Due to the wavy shaped structure of the conductor  130   b , the conductor  130   b  has better ductility to extend or compress during the conductive section  130  in a bending state, so that the conductor  130   b  is susceptible to stress of pulling and is not easily broken. Accordingly, the connection relationship between the conductor  130   b  and the connected LED chip  142  will be more stable, and the durability of the conductor  130   b  is also improved. 
     As shown in  FIG. 4I , in the present embodiment, the light conversion layer  120  disposing on the LED filament are embedded with different particles distributed therein corresponding to the positions of the LED sections  102 ,  104  and the conductive section  130  respectively. Moreover, the light conversion layer  120  disposing on corresponding regions of the LED sections  102 ,  104  and the conductive section  130  may have different structures, different materials, different effects, or different distribution densities. Because of the functions of the LED sections  102 ,  104  and the conductive section  130  are different, and thus the light conversion layer  120  disposed thereon may be respectively provided with different types of particles to achieve different effects. For example, the light conversion layer  120  corresponding to the LED sections  102 ,  104  may include phosphor particles  124   a , while the light conversion layer  120  corresponding to the conductive section  130  includes the light conducting particles  124   b . The phosphor particles  124   a  can absorb the light emitted by the LED chip  142  and convert the light wavelength to reduce or increase the color temperature, and the phosphor particles  124   a  also effect the light diffusion. Therefore, the phosphor particles  124   a  embedded in the light conversion layer  120  corresponding to the LED sections  102 ,  104  change the color temperature of the light and also make the light dispersion more uniform. The conductive section  130  does not have an LED chip, and the conductive section  130  has largest value of curvature in a state of bending the LED filament. Besides, the light conducting particles  124   b  has functions of enhancing the light diffusion and light transmission. Therefore, the light conducting particles  124   b  are embedded in the light conversion layer  120  corresponding to the conductive section  130  and used to direct the light from the adjacent LED sections  102 ,  104  into the conductive section  130  and further disperse evenly throughout the conductive section  130 . 
     The light conducting particles  124   b  are, for example, particles of different sizes made of polymethyl methacrylate (PMMA) or a resin, but not limited thereto. In some embodiments, the particles embedded in the conductive section  130  may also have highly elasto-plastic deformation properties, such as particles made of plastic, thereby improving the bendability of the conductive section  130  and enhancing the capability of self-sustained of the LED filament  100  in a state of bending. 
     As shown in  FIG. 4J , in the present embodiment, the light conversion layer  120  corresponding to the LED sections  102 ,  104  of the LED filament  100  includes light diffusing particles, such as phosphor particles  124   a , while the light conversion layer  120  corresponding to the conductive section  130  does not include the light diffusing particles. In the present embodiment, the light conversion layer  120  disposing on the LED sections  102 ,  104  and the conductive section  130  is made of, for example, a silicon gel, and no functional particles in the light conversion layer  120  corresponding to the conductive section  130 . In this way, it can improve the bendability of the conductive section  130 . 
     In some embodiments, the material of the light conversion layer  120  disposed on the conductive section  130  may be different from the material of the light conversion layer  120  disposed on the LED sections  102 ,  104 . For example, the light conversion layer  120  corresponding to the LED sections  102 ,  104  is made of silicone, and the light conversion layer  120  corresponding to the conductive section  130  is made of a light conducting material, for example, the light conversion layer  120  corresponding to the conductive section  130  may be made of PMMA, resin, or a combination thereof, but the present invention is not limited thereto. Since the material of the light conversion layer  120  disposing on the conductive section  130  is different from the material of the light conversion layer  120  disposing on the LED sections  102 ,  104 , the conductive section  130  and the LED sections  102 ,  104  may have different properties, for example, the conductive section  130  and the LED sections  102 ,  104  may have different elastic coefficient. Therefore, the LED sections  102 ,  104  has more supportive to protect the LED chips  142  and the conductive sections  130  has better bendability, and subsequently the LED filaments  100  can be bent to present a diverse curve. 
     As shown in  FIG. 4K , in the present embodiment, the LED sections  102 ,  104  and the conductive section  130  of the LED filament  100  have different contour features. In the present embodiment, the LED sections  102 ,  104  and the conductive section  130  have different widths, thicknesses or diameters in the radial direction of the LED filament  100 . In other words, the minimum distance between the opposite surfaces of the LED sections  102 ,  104  (that is, outer diameter of the LED sections  102 ,  104 ) is greater than the maximum distance between the opposite surfaces of the conductive section  130  (that is, outer diameter of the conductive section  130 ). As shown in  FIG. 4K , the outer diameter of the conductive section  130  is shorter than the outer diameter of the LED sections  102 ,  104 . When the LED filament  100  is bent, the conductive section  130  serves as a mainly bending region, and the thinner conductive section  130  is easier to bend with a variety of curves. 
     In this embodiment, the outer surface of the conductive section  130  is formed with a smooth transition curve between adjacent LED sections  102 ,  104 , and the outer diameter of the conductive section  130  is gradually thinner from an end adjacent to the LED sections  102 ,  104  toward to the middle of the conductive section  130 . That is, the junction of the conductive section  130  and the LED sections  102 ,  104  is provided with a smooth curve, therefore the LED filament in a state of bending, the stress can be dispersed and the stress does not concentrate at the junction between the conductive section  130  and the LED section  102 ,  104 . Therefore the possibility of crack or even rupture at the light conversion layer  120  can be reduced. In other embodiments, the outer diameter of the conductive section  130  may also be greater than the outer diameter of the LED sections  102 ,  104 , and the light conversion layer  120  disposing on the LED sections  102 ,  104  and the light conversion layer  120  disposing on the conductive section  130  may be made of different materials. For example, for the LED sections  102 ,  104 , the light conversion layer  120  is made of harder and supportive materials, and for the conductive section  130  the light conversion layer  120  is made of a flexible transparent encapsulation, such as PMMA, resin or other single material or composite material. 
     The various embodiments shown in  FIGS. 4A to 4K  may be implemented separately or in combination. For example, the LED filament  100  shown in  FIG. 4B  can be used in combination with the LED filament  100  shown in  FIG. 4D , that is, the conductive section  130  of the LED filament  100  has a wavy concave structure  132   a , and also embedded with auxiliary strip  132   c  inside the LED filament  100  to enhance the bendability and the capability of self-sustained of the LED filament. Alternatively, the LED filament shown in  FIG. 4I  can be used in combination with the LED filament shown in  FIG. 4G , that is, the particles distributed in the light conversion layer  120  corresponding to the LED sections  102 ,  104  have different sizes, different materials and/or different densities from the particles distributed in the light conversion layer  120  corresponding to the conductive section  130 . Moreover, the conductive section  130  further includes a spiral structure  132   e , so that not only the bendability but also the lighting uniformity of the LED filament is enhanced. Thereby the illumination of the omni-directional light is enhanced. 
     According to the structure of the LED filament  100  described above, as shown in  FIG. 5 , an LED filament  200  comprises a plurality of LED sections  202 ,  204 , a plurality of conductive sections  230 , at least two conductive electrodes  210 ,  212  and a light conversion layer  220 . The conductive section  230  is located between two adjacent LED sections  202 ,  204 . The two conductive electrodes  210 ,  212  are disposed on the LED filament  200  correspondingly and electrically connected to each of the LED sections  202 ,  204 . The adjacent two LED sections  202 ,  204  are electrically connected to each other through the conductive section  230 . Each of the LED sections  202 ,  204  includes at least two LED chips that are electrically connected to each other. The light conversion layer  220  covers the LED sections  202 ,  204 , the conductive sections  230  and the conductive electrodes  210 ,  212 , and a part of each of the two electrodes  210 ,  212  is exposed respectively. The LED filament  200  further includes a plurality of circuit films  240  (also referred to as light-transmitting circuit films). The LED chips  202  and  204  and the conductive electrodes  210  and  212  are electrically connected to each other through the circuit film  240 , and the light conversion layer  220  covers the circuit film  240 . The length of the circuit film  240  is less than the length of the conductor  230   a , or the shortest distance between two LED chips respectively located in two adjacent LED sections  202 ,  204  is greater than the distance between two adjacent LED chips in the LED section  202 / 204 . 
     Referring to  FIGS. 6A to 6G ,  FIG. 6A  is a schematic structural view of another embodiment of an LED filament of the present invention. One of the differences between the LED filament  400  shown in the  FIGS. 6A to 6G  and the LED filament  100  shown in the  FIGS. 4A to 4K  is the light conversion layer  420  of the LED filament  400  shown in the  FIGS. 6A through 6G  further providing with a two-layer structure. In some embodiments, each of the structural features of the LED filament  100  shown in  FIGS. 4C to 4K  can also be employed in the LED filament  400  shown in  FIG. 6A  or  FIG. 6B . As shown in  FIG. 6A , the LED filament  400  has a light conversion layer  420 , LED sections  402 ,  404 , conductive electrodes  410 ,  412 , and a conductive section  430  for electrically connecting adjacent two LED sections  402 ,  404 . Each of the LED sections  402 ,  404  includes at least two LED chips  442  that are electrically connected to each other by the wires  440 . In the present embodiment, the conductive section  430  includes at least one conductor  430   a  that connects the adjacent LED sections  402 ,  404 , wherein the shortest distance between the two LED chips  442  respectively located in the two adjacent LED sections  402 ,  404  is greater than the distance between two adjacent LED chips  442  within the one LED section  402 / 404 . Therefore, it is ensured that when the two LED sections  402 ,  404  are bent, the conductive section  430  is not easily broken due to the stress of bending. The length of the wire  440  is less than the length of the conductor  430   a . The light conversion layer  420  is coated on at least two sides of the LED chip  442  and conductive electrodes  410 ,  412 , and a portion of each of the conductive electrodes  410 ,  412  is not coated with the light conversion layer  420 . The light conversion layer  420  may have at least one top layer  420   a  (or upper layer) and one base layer  420   b  (or lower layer). In the present embodiment, the top layer  420   a  and the base layer  420   b  are disposed on the opposing surface of the LED chip  442  and conductive electrodes  410 ,  412 , and a portion of each of the conductive electrodes  410 ,  412  is excluded. It should be particularly noted that the thickness, diameter or width of the top layer  420   a  in the LED sections  402 ,  404  or the conductive section  430  described pertaining to  FIGS. 6A-6M  refers in radial direction of the LED filament. The thickness of the top layer  420   a  is the distance between its outer surface to the interface of the top layer  420   a  and the base layer  420   b , or the distance from its outer surface and the interface of the LED chip  442  or the conductor  430   a  and the base layer  420   b , wherein the outer surface of the top layer  420   a  is a surface away from the base layer. 
     In the present embodiment, the top layer  420   a  and the base layer  420   b  may be composed with different particles or particle densities according to the requirements or designed structures. For example, in the case where the main emitting surface of the LED chip  442  is toward to the top layer  420   a  but not the base layer  420   b , the base layer  420   b  may be composed of light scattering particles to increase the light dispersion. Thereby the brightness of the base layer  420   b  can be maximized, or even the brightness that can be produced close to the top layer  420   a . In addition, the base layer  420   b  may also be composed of phosphor particles with high density to increase the hardness of the base layer  420   b . In the manufacturing process of the LED filament  400 , the base layer  420   b  may be prepared first, and then the LED chip  442 , the wire  440  and the conductor  430   a  are disposed on the base layer  420   b . Since the base layer  420   b  has a hardness that can support the subsequent manufacturing process of the LED chips and the wires, therefore the yield and the firmness of the LED chips  442 , the wires  440 , and the conductors  430   a  disposed on the base layer  420   b  can be improved and resulted in less or even no sink or skew. Finally, the top layer  420   a  is overlaid on the base layer  420   b , the LED chip  442 , the wires  440 , and the conductor  430   a.    
     As shown in  FIG. 6B , in the present embodiment, the conductive section  430  is also located between the two adjacent LED sections  402 ,  404 , and the plurality of LED chips  442  in the LED sections  402 ,  404  are electrically connected to each other through the wires  440 . However, the conductor  430   a  in the conductive section  430  in  FIG. 6B  is not in the form of a wire but in a sheet or film form. In some embodiments, the conductor  430   a  can be a copper foil, a gold foil, or other materials that can conduct electrical conduction. In the present embodiment, the conductor  430   a  is attached to the surface of the base layer  420   b  and contact with the top layer  420   a , that is, located between the base layer  420   b  and the top layer  420   a . Moreover, the conductive section  430  and the LED sections  402 ,  404  are electrically connected by wires  450 , that is, the two closest LED chips  442  respectively located in the adjacent two LED sections  402 ,  404  are electrically connected by the wires  450  and the conductors  430   a  of the conductive section  430 . Wherein, the length of the conductive section  430  is greater than the distance between two adjacent LED chips of one LED sections  402 ,  404 , and the length of the wire  440  in the LED sections  402 ,  404  is less than the length of the conductor  430   a . This design ensures that the conductive section  430  has good bendability. Assuming that the maximum thickness of the LED chip in the radial direction of the filament is H, the thickness of the conductive electrode and the conductor  430   a  in the radial direction of the filament is around 0.5H to 1.4H, preferably around 0.5H to 0.7H. This ensures the wire bonding process can be carried out while ensures the quality of the LED filament and the precision of the wire bonding process, thereby the LED filament has good strength and the stability of the product is improved. 
     As shown in  FIG. 6C , in the present embodiment, the LED sections  402 ,  404  and the conductive section  430  of the LED filament have different structural features. In the present embodiment, the LED sections  402 ,  404  and the conductive section  430  have different widths, thicknesses, or diameters in the radial direction of the LED filaments. As shown in  FIG. 6C , the conductive section  430  is relatively thinner compared to the LED sections  402 ,  404 , therefore it is helpful to the LED filament curling to various curves. In the present embodiment, the base layer  420   b  is substantially uniform in width, thickness or diameter in the radial direction of the LED filament, whether in the LED sections  402 ,  404  or in the conductive section  430 . And, the top layer  420   a  has different widths, thicknesses or diameters in the radial direction of the LED filaments for the LED section  402 ,  404  and the conductive section  430 . As shown in  FIG. 6C , the top layer  420   a  of the LED sections  402 ,  404  has a maximum diameter D2 in the radial direction of the LED filament, while the top layer  420   a  of the conductive section  430  has the largest diameter D1 in the radial direction of the LED filament, D2 will be greater than D1. The diameter of the top layer  420   a  is gradually reduced from the LED sections  402 ,  404  toward to the conductive section  430 , and is gradually increased from the conductive section  430  toward to adjacent LED sections  402 ,  404 , so that the top layer  420   a  is conformally covered the LED filament and forms a smooth concave-convex curve along the axial direction of the LED filament. 
     As shown in  FIG. 6D , in the present embodiment, the top layer  420   a  of the LED sections  402 ,  404  has the largest diameter (or maximum thickness) in the radial direction of the LED filament and the diameter of the top layer  420   a  is gradually reduced from the LED sections  402 ,  404  to the conductive section  430 , and a portion of the conductor  430   a  (for example, the intermediate portion) is not covered by the top layer  420   a . The base layer  420   b , whether in the LED sections  402 ,  404  or in the conductive section  430 , has substantially the same width, thickness or diameter in the radial direction of the LED filament. In the present embodiment, the number of LED chips  442  in each of the LED sections  402 ,  404  may be different. For example, some LED sections  402 ,  404  have only one LED chip  442 , and some LED sections  402 ,  404  have two or more LED chips  442 . In addition to the number of the LED chip  442  designing in each LED section  402 ,  402  is different, the types of the LED chip  442  may also be different. It is acceptable as well that the number of the LED chip  442  designing in each LED section  402 ,  402  is consistent, and the types of the LED chip  442  is different. 
     As shown in  FIG. 6E , in the present embodiment, the top layer  420   a  is substantially uniform in width, thickness or diameter in the radial direction of the LED filament, whether in the LED sections  402 ,  404  or in the conductive section  430 . A portion of the base layer  420   b  has been recessed or hollowed out corresponding to a portion of at least one conductor  430   a , for example, the intermediate portion of the at least one conductor  430   a  is not covered by the base layer  420   b , and at least one of the other conductors  430   a  is completely covered by the base layer  420   b.    
     As shown in  FIG. 6F , in the present embodiment, the top layer  420   a  is substantially uniform in width, thickness or diameter in the radial direction of the LED filament, whether in the LED sections  402 ,  404  or in the conductive section  430 . A portion of the base layer  420   b  has been recessed or hollowed out corresponding to a portion of each conductor  430   a , for example, the intermediate portion of the conductor  430   a  is not covered by the base layer  420   b.    
     As shown in  FIG. 6G , in the present embodiment, the top layer  420   a  of the LED sections  402 ,  404  has the largest diameter in the radial direction of the LED filament, and the diameter of the top layer  420   a  is gradually decreased from the LED sections  402 ,  404  to the conductive section  430 . Moreover, a portion of the conductor  430   a  (for example, the middle portion) is not covered by the top layer  420   a , and a portion of the base layer  420   b  is recessed or hollowed out such that a portion of the conductor  430   a  (for example, the intermediate portion) is not covered by the base layer  420   b . In other words, at least a portion of the conductor  430   a  at the opposite sides thereof are not covered by the top layer  420   a  and the base layer  420   b , respectively. 
     As described above with respect to the embodiments of  FIGS. 6E to 6G , when the base layer  420   b  has a recession region or hollow region corresponding to a part of or all of the conductive sections  430 , and the recession region or the hollow region may be in the form of a slit or a groove. Therefore, the conductor  430   a  is not completely exposed and the conductive section  430  can be provided with better bendability. 
     As shown in  FIG. 6H , in the present embodiment, the conductor  430   a  is, for example, a conductive metal sheet or a metal strip. The conductor  430   a  has a thickness Tc, and since the thickness of the LED chip  442  is thinner than the conductor  430   a , the thickness Tc of the conductor  430   a  is significantly greater than the thickness of the LED chip  442 . In addition, with respect to the thickness of the LED chip  442 , the thickness Tc of the conductor  430   a  is closer to the thickness of the top layer  420   a  at the conductive section  430 , for example, Tc=(0.7˜0.9)×D1, preferably Tc=(0.7˜0.8)×D1. In the meanwhile, the thickness of the top layer  420   a  in the conductive section  430  can refer to the diameter D1 in the radial direction of the aforementioned top layer  420   a . Furthermore, in the present embodiment, the thickness of the top layer  420   a  disposed on the LED sections  402 ,  404  and on the conductive section  430  is substantially consistent with the same. In the meanwhile, the thickness of the top layer  420   a  in the LED sections  402 ,  404  can be referred to the diameter D2 in the radial direction of the aforementioned top layer  420   a.    
     As shown in  FIG. 6I , in the present embodiment, the thickness Tc of the conductor  430   a  is also significantly greater than the thickness of the LED chip  442 , and the thickness Tc of the conductor  430   a  is closer to the thickness of the top layer  420   a  on the conductive section  430  (diameter D1). Also, in the present embodiment, the thickness of the top layer  420   a  in the conductive section  430  and that in the LED sections  402 ,  404  are inconsistent. As shown in  FIG. 6I , the top layer  420   a  of the LED sections  402 ,  404  has a minimum diameter D2 in the radial direction of the LED filament, while the top layer  420   a  of the conductive section  430  has the largest diameter D1 in the radial direction of the LED filament, D1 will be greater than D2. The diameter of the top layer  420   a  is gradually increased from the LED sections  402 ,  404  to the conductive section  430 , and is gradually reduced from the conductive section  430  to the LED sections  402 ,  404 , so that the top layer  420   a  forms a smooth concave-convex curve along the axial direction of the LED filament. 
     As shown in  FIG. 6J , in the present embodiment, the thickness Tc of the conductor  430   a  is also significantly greater than the thickness of the LED chip  442 , however, the top layer  420   a  of the LED sections  402 ,  404  has the largest diameter in the radial direction of the LED filament. The diameter of the top layer  420   a  is gradually reduced from the LED sections  402 ,  404  to the conductive section  430 , and a portion of the conductor  430   a , for example the intermediate portion, is not covered by the top layer  420   a.    
     As shown in  FIG. 6K , in the present embodiment, the thickness of the conductor  430   a  is also significantly larger than the thickness of the LED chip  442 . Besides, compared with the thickness of the LED chip  442 , the thickness of the conductor  430   a  is closer to the thickness of the top layer  420   a  corresponding to the conductive section  430 . In the width direction of the LED filament, the top layer  420   a  has a width W1, and the LED chip  442  has a width W2, and the width W2 of the LED chip  442  is close to the width W1 of the top layer  420   a , wherein the width direction is perpendicular to both the axial direction and the aforementioned thickness direction. That is, the top layer  420   a  is slightly larger than the LED chip  442  in the width direction and slightly larger than the conductor  430   a  in the thickness direction. In other embodiments, the ratio of the width W1 of the top layer  420   a  to the width W2 of the LED chip  442  is around 2 to 5, i.e., W1:W2=2˜5:1. In the present embodiment, the base layer  420   b  has the same width W1 as the top layer  420   a , but is not limited thereto. In addition, as shown in  FIG. 6K , in the present embodiment, the conductive section  430  further includes a wavy concave structure  432   a  disposed on one side surface of the conductive section  430 . In the present embodiment, the wavy concave structure  432   a  is recessed by the upper side surface of the top layer  420   a  of the conductive section  430 . The plurality of wavy concave structures  432   a  are spaced apart in the axial direction and are parallel to each other to present a continuous wave shape. In some embodiments, the plurality of wavy concave structures  432   a  are continuously closely aligned along the axial direction. In some embodiments, the wavy concave structure  432   a  may also be disposed around the entire circumferential surface of the conductive section  430  centering on the axial direction of the LED filament. In some embodiments, the wavy concave structure  432   a  may also be replaced by a wavy convex structure (as shown in  FIG. 4C ). In some embodiments, the wavy concave structure and the wavy convex structure may be staggered together to form a wavy concave-convex structure. 
     As shown in  FIG. 6L , in the present embodiment, the LED chip  442  has a length in the axial direction of the LED filament and has a width in the X direction, and the ratio of the length to the width of the LED chip  442  is around 2:1 to 6:1. For example, in one embodiment, two LED chips are electrically connected as one LED chip unit, and the LED chip unit can have an aspect ratio of 6:1, which enables the LED filament to have a larger luminous flux. Moreover, the LED chip  442 , the conductive electrodes  410 ,  412  and the conductor  430   a  have a thickness in the Y direction, the thickness of the conductive electrodes  410 ,  412  is smaller than the thickness of the LED chip  442 , and the thickness Tc of the conductor  430   a  is also smaller than the thickness of the chip  442 , that is, the conductor  430   a  and the conductive electrodes  410 ,  412  are thinner than the chip  442 . Further, the top layer  420   a  and the base layer  420   b  have a thickness in the Y direction, and the thickness of the base layer  420   b  is smaller than the maximum thickness of the top layer  420   a . In the present embodiment, the shape of the conductor  430   a  is a parallelogram rather than a rectangle in the top view along the Y direction, that is, the angle of the four sides of the conductor  430   a  is not 90 degrees presented in the top view. In addition, the two ends of the LED chip  442  are respectively connected to the wire  440  or the wire  450  and to be connected to the other chip  442  or the conductor  430   a  through the wire  440  or the wire  450 . Furthermore, the connection points of the two ends of the LED chip  442  using to connect with the wire  440  or the wires  450  are not aligned with each other in the axial direction of the LED filaments. For example, the connection point of one end of the chip  442  is offset toward the negative X direction, and the connection point of the other end of the chip  442  is offset toward the positive X direction, that is, there will be a distance between the two connection points of the two ends of the chip  442  in the X direction. 
     A wavy concave or convex structure  432   a  as shown in  FIG. 6K , which is a wave shape showing depressions and ridges in the Y direction, and is kept linear perpendicularly to the axial direction of the LED filament in the top view. It is to be noted that each groove of the wavy concave structure  432   a  or each protrusion of convex structure  432   a  is a straight line perpendicularly arranged along the axial direction of the LED filament, or the line connecting the lowest point of each groove of the wavy concave structure  432   a  in the Y direction is a straight line or the line connecting the highest point of each protrusion of the convex structure  432   a  in the Y direction is a straight line. The wavy concave or convex structure  432   a  as shown in  FIG. 6L  is not only wavy in the Y direction but also curved in the axial direction of the LED filament in the top view, that is, each groove of the wavy concave structure  432   a  and each protrusion of convex structure  432   a  is separately curved in a straight line and the two straight lines are perpendicularly arranged along the axial direction of the LED filament. Moreover, a line connecting the lowest point of each groove of the wavy concave structure  432   a  in the Y direction or a line connecting the highest point of each protrusion of the convex structure  432   a  in the Y direction is in a curve. 
     As shown in  FIG. 6M , which is a partial top view of the conductive section  430  of  FIG. 6L .  FIG. 6M  presents a wavy concave or convex structure  432   a  and  FIG. 6L  presents a curved configuration of the conductive section  430  in the axial direction of the LED filament. Moreover, in the present embodiment, the width of each groove of the wavy concave structure  432   a  itself in the axial direction of the LED filament is irregular, that is, the width of any two places of each groove is unequal. For example, two places of a certain groove of the wavy concave structure  432   a  in  FIG. 6M  have a width D1 and a width D2 respectively, and the width D1 and the width D2 are not equal. In addition, in the present embodiment, the width of each groove of the wavy concave structure  432   a  in the axial direction of the LED filament is also irregular. For example, each groove of the wavy concave structure  432   a  is aligned in parallel along the axial direction of the LED filament, however, the widths of each grooves are unequal. For example, two adjacent grooves of the wavy concave structures  432   a  in  FIG. 6M  have a width D1 and a width D3 at two positions aligned in the axial direction, and the width D1 and the width D3 are not equal. In other embodiments, the shape of the wavy concave or convex structure  432   a  is a straight strip or a combination of a straight strip and a wave from the top view of the conductive section. In other words, the surface of the top layer  420   a  at the conductive section  430  can be a straight line or a combination of a straight line and a wavy line in the side view. 
       FIG. 7  illustrates another embodiment of an LED filament layered structure. In the present embodiment, the LED sections  402 ,  404 , the gold wires  440 , and the top layer  420   a  are disposed on both sides of the base layer  420   b , that is, the base layer  420   b  is located between the two top layers  420   a . The conductive electrodes  410 ,  412  are respectively disposed at both ends of the base layer  420   b . As shown in the figure, the LED sections  402 ,  404  in the upper and lower top layers  420   a  can be connected to the same conductive electrode  410 / 412  by gold wires  440 , in this way, the light ray distribution can be more uniform. Moreover, the gold wire  440  may be bent with posture to reduce the impact force, the posture may be, for example, slightly M-shape in  FIG. 4H , curve or straight shape. 
       FIG. 8  illustrates another embodiment of the LED filament layered structure of the present invention. As shown in  FIG. 8 , the light conversion layer of LED filament  400  includes a top layer  420   a  and a base layer  420   b . Each side of the LED sections  402 ,  404  is in direct contact with the top layer  420   a , and the base layer  420   b  is not in contact with the LED sections  402 ,  404 . In the manufacturing process, the base layer  420   b  can be formed in advance, and the LED sections  402 ,  404  and the top layer  420   a  are formed successively. 
     In another embodiment, as shown in  FIG. 9 , the base layer  420   b  of the LED filament  400  is formed with a wavy surface accompanying undulations, then the LED sections  402 ,  404  are disposed thereon and consequently are inclined to different directions. Thus, the LED filament has a broader light emitting angle. That is to say, from the side view, the LED sections is arranged with different angles with respective to the horizontal plane rather than in parallel to the horizontal plane, wherein the horizontal plane is defined by the interface of the bottom surface of the base layer and the surface of the carrier, and the carrier is used to provide the supporting in the manufacturing process. Furthermore, the configured height/angle/direction between each LED section can also be different. In other words, a plurality of LED sections are connected in series and not aligning in a straight line. In this way, the filament  400  has the effect of increasing the emitting angle and the uniformity of the light without being bent or curved. 
     In the LED filament structure as shown in  FIG. 10 , the filament  400  includes at least one LED section  402 ,  404 , at least one pair of conductive electrodes  410 ,  412 , a plurality of gold wires  440 , a light conversion layer  420 , and at least one conductive section  430  electrically connecting the two adjacent LED sections  402 ,  404 . Wherein each of the LED sections  402 ,  404  includes at least two LED chips  142  that are electrically connected to each other by wires  440 . The light conversion layer  420  includes a base layer  420   a  and a top layer  420   b , and a copper foil  460  having a plurality of openings is attached to the base layer  420   a . The upper surface of the copper foil  460  may further have a silver plating layer  461 , and the copper foil located at each end of the LED filament as a conductive electrode  410 ,  412  and extending beyond the light conversion layer  420 . Subsequently, the LED sections  402 ,  404  can be disposed to the base layer  420   a  by means of die bond paste or the like. Thereafter, a phosphor glue or phosphor film is applied to coat the LED sections  402 ,  404 , gold wire  440 , conductive section  430 , and a portion of the conductive electrodes  410 ,  412  to form a light conversion layer  420 . The width or/and length of the opening of the copper foil  460  is greater than that of the LED chip  442 , defining the position of the LED chip. At least two of the six faces of the LED chip, generally five faces in the present embodiment, being covered by the phosphor glue. In the present embodiment, the combination of copper foil  460  and the gold wire  440  provides a solid conductive structure and also maintaining the flexibleness of the LED filament. Besides, the silver plating layer  461  has an effect of increasing light reflection in addition to good electrical conductivity. 
     In the LED filament package structure as shown in  FIG. 11 , the LED filament  400  is similar to the LED filament disclosed in  FIG. 10 , and the difference is that: (1) the LED chip  442  used for the filament  400  is a flip chip having the same solder pad height, wherein the solder pad is directly connected to the silver plating layer  461 ; (2) the length of the opening of the LED filament described aforemention (that is, the length in the axial direction of the LED filament) must be greater than the LED chip  442  in order to accommodate the LED chip  442 , furthermore, the LED chip  442  of the LED filament in the present embodiment is located corresponding to the opening  432  and above the copper foil  460 /silver plating layer  461 , therefore the length of the LED chip  442  is greater than the opening  432 . The present embodiment omits the step of gold wire bonding in compared to the previous embodiment. 
     The LED filament structures as shown in  FIG. 11  can be employed. The feature of the LED filament structure is that the LED chip is used as flip-chip configuration, that is, the original height of the different solder pads is processed to the same height, usually the lower N-pole extension is processed to the same height as the P-pole. 
     In an embodiment, the tubular encapsulation of the LED filament is a monolithic structure. In some embodiments, the monolithic structure shares a uniform set of chemical and physical properties throughout the entire structure. Being structurally indivisible, the monolithic structure need not be a uniform structure. In other embodiments, the monolithic structure includes a first portion and a second portion having a different property from the first portion. In another embodiment, the tubular encapsulation includes a set of otherwise divisible layers or divisible columns interconnected to form a unitary structure of the tubular encapsulation. In  FIGS. 12 and 13 , the tubular encapsulation of an LED filament includes a set of interconnected divisible columns configured to form a unitary structure of the tubular encapsulation. Referring to  FIG. 12 , the LED filament  400  is further cut into two parts to schematically show its internal structure. Wherein the set of interconnected divisible columns includes a plurality of alternating columns and each column can be configured to a first light conversion layer  420   a  or a second light conversion layer  420   b . The tubular encapsulation of the LED filament includes at least one LED section  402 ,  404 , a plurality of columns  420 , at least one conductive section  430  and at least one conductive electrode  410 . The conductive section  430  is located between the adjacent two LED sections  402 ,  404 . The conductive electrode  410  is electrically connected to the LED section  402 / 404 . The LED sections  402 ,  404  are enclosed by the column of first light conversion layer  420   a , and the conductive section  430  is enclosed by the column of second light conversion layer  420   b . In one embodiment, the LED sections  402 / 404  include a plurality of LED chips  442 . The adjacent two LED sections  402 ,  404  are electrically connected by the conductive section  430 , and the conductive section  430  includes a conductor  430   a . The conductor  430   a  is mainly disposed in the conductive section  430  and two ends of conductor  430   a  are disposed in the adjacent sections  402 ,  404 . In another embodiment, the LED chips  442  are disposed in the LED sections  402 / 404  and both ends of the conductor  430   a  for connecting the two shortest distance LED chips in the adjacent two LED sections  402 ,  404  are disposed in the conductive section  430 . In another embodiment, LED chips  442  are disposed in LED sections  402 / 404 . A portion of the conductor  430   a  for electrically connecting the adjacent two LED sections  402 ,  404  is disposed in the first light conversion layer  420   a , and another portion is disposed in the second light conversion layer  420   b . The properties of the first light conversion layer  420   a  and the second light conversion layer  420   b  may be different, depending on the advantages an LED filament is expected to pursue. Wherein the properties such as the converted wavelength, size of integrated particle, thickness, transmittance, hardness, composition ratio, etc. In one embodiment, the first light conversion layer  420   a  is harder than the second light conversion layer  420   b , and the first light conversion layer  420   a  is filled with more phosphor particles than the second light conversion layer  420   b . Because the first light conversion layer  420   a  is a relatively harder layer, it is configured to better protection of the linear array of LED sections  402 / 404  and ensuring that the LED light bulb does not malfunction when the LED filament is bent to maintain a desired posture in the LED light bulb. The second light conversion layer  420   b  is a relatively softer layer so that the entire LED filament is bent with posture in the LED light bulb to produce omni-directional light, especially one single LED filament producing omni-directional light. In another embodiment, the first light conversion layer  420   a  has a better thermal conductivity than the second light conversion layer  420   b , such as more heat dissipating particles added to the first light conversion layer  420   a  than the second light conversion layer  420   b . The first light conversion layer  420   a  having a higher thermal conductivity can conduct heat generated from the LED sections out of the LED filament, thereby the linear array of LED sections has better protection free from degradation or burning. Because of the conductive section  430  and the LED section  402 / 404  are interval disposed and the conductive section  430  further acts less than the LED sections  402 / 404  in terms of the heat conduction. Therefore, when the second light conversion layer  420   b  is contained with less heat dissipating particles than the first light conversion layer  420   a , the cost of manufacturing of the LED filament can be saved. The size ratio of each columns of the first light conversion layer  420   a  enclosing the LED sections  402 / 404  and the tubular encapsulation of the LED filament is determined by reference factors such as light conversion capability, bendability, thermal conductivity. Other cases are the same, the larger volume of the first light conversion layer  420   a  in compare with the entire tubular encapsulation of the LED filament, the LED filament has greater light conversion capability and thermal conductivity, but will not be easy to be bent. The circumferential surface of the entire tubular encapsulation of the LED filament shows a combination surface of the first light conversion layer  420   a  and other regions. A ratio R5 is defined as the ratio of the circumferential surface of the first light conversion layer  420   a  to the total circumferential surface of the entire tubular encapsulation of the LED filament. Preferably, the ratio R5 is from 0.2 to 0.8. Preferably, the ratio R5 is in a range of around 0.4 to 0.6. 
     In the structure of the LED filament  400  shown in  FIG. 13  is similar to  FIG. 12 , the difference is the placement of the second wire  450 . The LED chips  442  are disposed in each LED sections  402 / 404 . The LED sections  402 ,  404  are electrically connected to the conductive sections  430  or the LED chips  442  of the LED sections  402 / 404 , for example, electrically connected by a first wire  440  and a second wire  450 , and the second wire  450  is disposed in the conductive section  430 . In another embodiment, a portion of certain LED chips  442  in the LED sections  402 / 404  are enclosed in the LED sections  402 / 404 . Both ends of the wire for connecting the two shortest distance LED chips in the adjacent two LED sections  402 ,  404  are disposed in the second light conversion layer  420   b , that is, the second wire is disposed in the second light conversion layer  420   b . In another embodiment, the LED chips  442  are enclosed in the LED sections  402 / 404 . A portion of the second wire  450  for electrically connecting the adjacent LED chip  442  and the conductor  430   a  is disposed in the first light conversion layer  420   a , and another portion of the second wire  450  is disposed in the second light conversion layer  420   b.    
     The connection mode between the conductor in the conductive section and the light conversion layer is described as follows. Referring to  FIG. 14A , in the LED filament structure shown in  FIG. 14A , the LED filament  400  has a light conversion layer  420 , the LED sections  402 ,  404 , the conductive electrodes  410 ,  412 , and at least one conductive section  430 . The conductive section  430  is located between adjacent LED sections  402  and  404 . The LED sections  402  and  404  include at least two LED chips  442  electrically connected to each other through the wires  440 . In the present embodiment, the conductive section  430  includes a conductor  430   a . The conductive section  430  and the LED sections  402 ,  404  are electrically connected by wires  450 , that is, two LED chips respectively located in the adjacent two LED sections  402 ,  404  and closest to the conductive section  430  are electrically connected to each other through the wires  450  connecting with the conductor  430   a  in the conductive section  430 . The length of the conductive section  430  is greater than the distance between two adjacent LED chips in one single LED sections  402 ,  404 , and the length of the wire  440  is less than the length of the conductor  430   a . The light conversion layer  420  is disposed on at least one side of the LED chip  442  and the conductive electrode  410 ,  412 , and a part of the two conductive electrodes is exposed from the light conversion layer. The light conversion layer  420  includes at least a top layer  420   a  and a base layer  420   b . In the present embodiment, the LED sections  402 ,  404 , the conductive electrodes  410 ,  412 , and the conductive section  430  are all attached to the base layer  420   b.    
     The conductor  430   a  can be a copper foil or other electrically conductive material, and the conductor  430   a  has opening. The upper surface of the conductor  430   a  may further have a silver plating layer, and subsequently, the LED chip  442  may be attached to the base layer  420   b  by means of die bond paste or the like. Thereafter, a phosphor glue or phosphor film is applied to coat over the LED chip  442 , the wires  440 ,  450 , and a portion of the conductive electrodes  410 ,  412  to form a light conversion layer  420 . The width or/and the length of the opening of the conductor  430   a  are respectively larger than the width or/and the length of the LED chip  442  and defining the position of the LED chip  442 . At least two of the six faces of the LED chip, generally five faces in the present embodiment, being covered by the phosphor glue. The wires  440 ,  450  may be gold wires. In the present embodiment, the combination of copper foil  460  and the gold wire  440  provides a solid conductive structure and also maintaining the flexibleness of the LED filament. Besides, the silver plating layer  461  has an effect of increasing light reflection in addition to good electrical conductivity. 
     In an embodiment, the shape of the conductor may also result from considering the gold wire connection or filament bending. For example, in one embodiment, a top view of conductor  430   a  is shown in  FIG. 14B , the conductor  430   a  has a joint region  5068  and a transition region  5067 . The joint region  5068  is at the end of the conductor  430   a  for being electrically connected with other components. In the present embodiment, the conductor  430   a  comprises two joint regions  5068 , and the transition region  5067  is located between two joint regions  5068  and for connecting the two joint regions  5068 . The width of the joint region  5068  may be greater than that of the transition region  5067 . Since the joint region  5068  is used to serve as a pad for electrical contact, a relatively sufficient width is required. For example, if the width of the LED filament is W, the width of the joint region  5068  of the conductor  430   a  can be between around ¼ W and W. The joint region  5068  can be multiple and the width thereof may be not consistent. Because the transition region  5067  between the joint regions  5068  is not required to form any joint point, the width can be less than that of the joint region  5068 . For example, if the width of the LED filament is W, the width of the transition region  5067  can be between 1/10 W and ⅕ W, the conductor  430   a  is easily to be bent along with the bending of the filament due to the less width of the transition region  5067  of the conductor  430   a ; therefore, the risk that a wire close to the conductor may be easily broken by stress of bending is lower. 
     In one embodiment, as shown in the top view of  FIG. 14C , one of the LED chips  442  constituting an LED filament is connected to the conductor  430   a  via the wire  450 , wherein the conductor  430   a  has two openings like notch or rabbet with the quadrilateral shape symmetrically at the two terminals of the conductor  430   a . Therefore, the LED chip disposing in the opening has three sides opposite to the part of the conductor  430   a . Moreover, two terminals of the conductor  430   a  being defined as the transition region  5067  and the middle area between the terminals being defined as the joint region  5068  having a width Wc. Furthermore, each transition region  5067  of the conductor  430   a  is divided into two strips with the width Wt1 and Wt2 symmetrically aligned with the longitudinal centerline of the conductor  430   a . Moreover, the sum of the widths of the two strips of the transition regions  5067 , that is the width Wt1 and Wt2, is less than the width of the joint region  5068  Wc. As shown in  FIG. 14C , the sum of the widths Wt1, Wt2 of the two strips of the transition regions  5067  is less than the width We of the joint region  5068  in the direction perpendicular to the longitudinal of the LED filament, which can increase the mechanical strength between the conductor and the LED chip  442  of the LED filament and also to avoid the damage of the wires  450  connecting the LED chips and the conductors. In an embodiment, the length of the strip of the transition region may extend to the LED section adjacent to the conductive section in the longitudinal direction of the LED filament, thereby slow down the impact of the external force on the LED chip and improving product stability. In the present embodiment, the width We of the joint region  5068  is equal to the width of the base layer  420   b  or the width of the LED filament, and the side of the LED chip  442  disposing in the opening without opposing the conductor  430   a  is electrically connected to other LED chips through the wire  440 . The length of the wire  450  between the LED chip  442  and the conductor  430   a  is shorter than the distance between any two LED chips in the LED section. For example, the length of the wire between the LED chip  442  and the conductor  430   a  is shorter than the distance between two adjacent LED chips in the LED section. As a result, the risk of the LED filaments being broken caused by the elastic setback stress is also lower. 
     In one embodiment, the conductor  430   a  in the LED filament has a contour consisting of a joint region  5068  and four strip shaped transition regions  5067  as shown in  FIG. 14C . Further, the conductor  430   a  can be illustrated with a left half portion and a right half portion symmetrically aligned with the short axis centerline thereof such as a left half portion or a right half portion of the bottom view shown in the  FIG. 14E ,  FIG. 14G ,  FIG. 14H  and  FIG. 14I . In other embodiments, the conductor  430   a  may not having symmetric contour with respect to the short axis centerline thereof, and the transition region  5067  for connecting the joint regions  5068  may be any combination of the transition regions  5067  shown in  FIG. 14E ,  FIG. 14F , and  FIGS. 14G, 14H, and 14I . As shown in  FIG. 14J , the conductor  430   a  has at least one through hole  506   p , and also referring to  FIG. 14D  and  FIG. 14E .  FIG. 14D  is a cross sectional view of the conductor  430   a  and the  FIG. 14E  is a bottom view shown a left half portion or a right half portion of the conductor  430   a  in the  FIG. 14D . Wherein the base layer  420   b , for example the phosphor film, infiltrates the hole  506   p  from one end, and optionally selected to fill up to the other end of the hole  506   p . The phosphor film showed in  FIG. 14D  is not filled to the overflow through hole. Moreover, in the present embodiment, the upward surface of  FIG. 14D  is roughened so that the surface thereof has better thermal dissipation capability. In other embodiments, the conductor  430   a  may be located between the top layer  420   a  and the base layer  420   b  as shown in  FIG. 14L , the base layer  420   b  has a beveled groove, and the through hole size of the conductor  430   a  is smaller than the maximum size of the bevel groove of the base layer  420   b . Therefore, when the phosphor film, that is, the material of the top layer  420   a , overlies the conductor  430   a  and fills the through hole, the phosphor film in the bevel groove partially contacts the area under the conductor  430   a . As shown in  FIG. 14L ,  FIG. 14L  is a cross sectional view taken along the line E 1 -E 2  of  FIG. 14K . The phosphor glue used to form the top layer  420   a  is filled into the through hole  506   p  of the conductor  430   a  and then further filled into the beveled groove of the base layer  420   a . In another embodiment, as shown in  FIG. 14M , the phosphor film used to form the base layer  420   b  is filled into the through hole  506   p  of the conductor  430   a  and then further filled till contacting the surface of the top layer  420   a . As shown in  FIG. 14L  and  FIG. 14M , since the conductor  430   a  is similarly riveted by the top layer  420   a  or the base layer  420   b  in the axial direction of the LED filament, the contact area between the conductor  430   a  and the top layer  420   a  or the base layer  420   b  is increased. The increase in the contact area that increases the bonding strength between the conductor  430   a  and the top layer  420   a  or the base layer  420   b , and the bendability of the conductive section is thereby improved. 
       FIGS. 14F, 14G, 14H and 14I  are embodiments of the conductors  430   a  having through holes. The  FIG. 14F  is a partial bottom view of an LED filament of an embodiment in which the conductor  430   a  has only one transition regions  5067  connected to the joint region  5068 , whether the transition region  5067  or the joint region  5068  has a rectangular shape. The  FIG. 14F  is a bottom view showing only a left half portion or a right half portion of the conductor  430   a  symmetrically aligned with the short axis centerline thereof, and it is arranged with one strip shaped transition region  5067  connected to the joint region  5068 . When the left half portion is combined with the right half portion, the contour of the conductor  430   a  may be any combination of the transition regions  5067  and the joint regions  5068  shown in  FIGS. 14E, 14F, 14G, 14H, and 14I . Taking the central point of the LED chip  442  as the center, the shortest distance from the center to the closest boundary of the joint region is set to r1, and the shortest distance from the center to the closest boundary of the transition region is set to r2. When the distance r1 is greater than or equal to the distance r2, the broken risk of the LED filament caused by the elastic frustration stress can be reduced. The  FIG. 14F  shows the case where r1 is greater than r2. In the case where the conductor  430   a  is enclosed by the base layer  420   b , for example a phosphor film, referring to schematic diagram of  FIG. 14F , the location of the chip  442  is present with the dotted line due to the chip  442  is blocked by the base layer  420   b . From the bottom view, it is seen that the LED chip  442  overlaps the portion of the transition region  5067 . In other embodiments, the LED chip  442  does not overlap the portion of the transition region  5067  in a bottom view. In other embodiments, the conductor comprises one joint region and two transition regions, one transition region  5067  can be connected to the middle of the joint region  5068 , and another transition region can be connected to the middle or one end of the joint region  5068 , alternatively, another transition region  5067  can also be connected to the joint region  5068  any position between the ends and the middle of the joint region  5068 . When another transition region  5067  is connected to the middle joint region  5068 , the transition region  5067  and the joint region  5068  form a shape like a cross in the bottom view. 
     The difference between embodiments showing in the  FIG. 14G  and  FIG. 14E  is the conductor  430   a  in the embodiment of  FIG. 14G  having simply two transition regions, each transition region  5067  of the conductor  430   a  having two symmetrical contours symmetrically arranged about the longitudinal axis of the LED filament and a portion of the contour is in contact with the joint region  5068 . For example, each transition region  5067  of the conductor  430   a  is in a shape of trapezoid extending from the boundary of the joint region  5068  and the shorter trapezoidal side away from the joint region  5068 . In other words, in the bottom view, the transition region  5067  has a fixed end, that is the boundary of the joint region  5068  connecting with the transition region  5067 , whose width is equal to the length of the long side of the trapezoid or the width of the joint region  5068  and the base layer  420   b . In other embodiments, the transition region  5067  whose width is gradually reduced from the fixed end to the other end may also be in a shape of triangular or semi-circular. The average width of the transition region  5067  is less than that of the joint region  5068 . As shown in  FIG. 14G , in the case where the embedded conductor  430   a  is enclosed by the base layer  420   b  (for example, a phosphor film), therefore the chip  442  is covered by the base layer  420   b  and from the bottom view the LED chip  442  illustrated by the dashed line is overlapped with the transition region  5067 . 
     The difference between the  FIG. 14H  and  FIG. 14F  is the transition region  5067  of  FIG. 14H  having two triangles symmetrical about the longitudinal axis of the LED filament, one lateral of the triangle is aligned with the outer side of the LED filament, and the other lateral is connected with the joint region  5068 , and the oblique lateral of the triangle has an end point intersecting with the joint region  5068  in the longitudinal axis of the LED filament. The triangle being symmetrical designed in the transition region  5067  may be an equilateral triangle, an acute triangle, or an obtuse triangle, etc. In the present embodiment, the two oblique laterals of the two symmetrically triangles are intersected, but are not limited thereto. The distance between two oblique laterals in parallel with the short axial direction of the LED filament will gradually increase along the distance move away from a fixed end to the other end, that is, the two oblique laterals respectively intersecting with the opposite sides of the base layer  420   b  at the other end. Wherein the fixed end is the boundary of the joint region  5068  connecting with the transition region  5067 . 
     The embodiment of  FIG. 14I  is similar to  FIG. 14H , the difference is the oblique lateral of the triangle of the transition region  5067  in  FIG. 14I  is not a straight line but a stepped shape. In other embodiments, the oblique lateral of the triangle of the transition region  5067  can be in the shape of curved, arched, or wavy. And all the structures described based on  FIG. 14C  to  FIG. 14I  also are able to be applied to the structure of electrode  410 ,  412 . 
     In other embodiments, the conductor  130   a  in  FIG. 4 , the conductor  230   a  in  FIG. 5 , and the conductor  430   a  in  FIGS. 7 to 9  may be the structure of the conductor  430   a  shown in  FIGS. 14A to 14O , and other components are unchanged. When the conductor  430   a  in  FIG. 7  is the structure of the conductor  430   a  shown in  FIGS. 14A to 14O , the rivet structure shown in  FIG. 14L  can be formed, and the material of the top layer  420   a  is filled in the hole  506   p  of the conductor  430   a  and further filled to the space between the conductor  430   a  and the base layer  420   b . Therefore, the contact area between the conductor and the top layer is increased that will lead to the improvement of the bonding strength between the conductor and the top layer, thereby the bendability of the conductive section is improved. 
     Since the LED filament is placed inside the LED light bulb with undulating posture, the bending portion with a small radian may be weakened by the thermal stress due to thermal expansion caused by the heat generating from the LED light bulb. Therefore, the holes or notches can be appropriately placed in the LED filament near the bending portion to mitigate this effect. In one embodiment, as shown in schematic diagram  FIG. 14N  which the LED chip and the conductive electrode of the LED filament are omitted, the region between the D1 to D2 is a predetermined bending portion. The conductor  430   a  is provided with a plurality of holes. Preferably, the size of the holes  468  are gradually increased from outer bending portion (showing as upper in the figure) to the inner thereof (showing as), and the hole  468  is triangular in the cross sectional view of the present embodiment. When the LED filament is bent upward by the F direction, the LED filament is easier to bent due to the plurality of holes  468  between the region from D1 to D2, and the hole  468  at the bending portion can buffer the thermal stress. Moreover, the deformation of the LED filament is followed the designed hole shape and the bending angle. 
       FIG. 14O  is a bending form of the LED filament shown in  FIG. 14A  of the present invention. In the related art, a plurality of LED filaments are generally connected by the conductive electrode to realize the requirement of curling the LED filament. Since the bending is occurred at the conductive electrode, the strength of that is less and easily to be broken, further, the conductive electrode takes up some space to make the light emitting area of the LED filament smaller. In the present invention, the conductive section  430  is a bent portion of the LED filament, and the rivet structure and the conductor reinforcement are formed by the conductor  430   a  shown in  FIGS. 14C to 14M , so that the wire  450  connecting the LED chip  442  and the conductor  430   a  is less likely to be broken. In various embodiments, the conductors may be arranged in a configuration as shown in  FIG. 14B  or provided with an accommodating space on the conductor  430   a  (e.g., the hole structure shown in  FIG. 14N ) to reduce the probability of the LED filament cracking during bending. The LED filament of the invention has the advantages of good bendability and high luminous efficiency. 
     The structure as shown in  FIG. 15 , the LED filament is similar to the LED filament disclosed in  FIGS. 14A to 14O , except that a copper foil  460  is disposed between the two LED chips  442 , and a silver plating layer  461  is disposed on the copper foil. The copper foil  460  is electrically connected to the LED chips  442  through the wire  440 . 
     The structure as shown in  FIG. 16 , the LED filament is similar to the LED filament disclosed in  FIGS. 14A to 14O , and the difference is that: (1) the LED chip used for the LED filament is a flip chip having the same solder pad height and the solder pad is directly connected to the silver plating layer; (2) the length of the aforementioned opening (e.g., opening  432  in  FIG. 11 ) of the LED filament in the longitudinal direction of the LED filament must be greater than the length of the LED chip to accommodate the LED chip, and the LED chip  442  of the LED filament of the present embodiment corresponds to the opening  432  is located above the copper foil  460  and the silver plating layer  461 , so the length of the LED chip  442  is greater than the length of the opening. 
     According to the aforementioned embodiments of the present invention, since the LED filament structure is provided with at least one LED section and at least one conductive section, when the LED filament is bent, the stress is easily concentrated on the conductive section. Therefore, the breakage probability of the gold wire connected between the adjacent LED chips is reduced during bending. Thereby, the quality of the LED filament and its application is improved. In addition, the conductive section employs a copper foil structure, which reduces the length of the metal wire bonding and further reduces the breakage probability of the metal wire during bonding. In other embodiments of the invention, in order to improve the bendability of the conductive section, and further prevent the conductor from damaged when the LED filament is bent. The conductor in the LED filament conductive section may be in a shape of “M” or wave profile for providing a better flexibility in extension of the LED filament. 
     Next, a related design of the layer structure of the LED filament structure will be described.  FIGS. 17A to 17C  are cross-sectional views of an LED filament according to different embodiments of the present invention. Surfaces of the filaments shown in  FIGS. 17A to 17C  are with different angles. The top layer  420   a  in  FIG. 17A ,  FIG. 17B ,  FIG. 17C  may be made by a glue dispenser, and viscosity adjustment to the phosphor glue is made so that both sides of the top layer after the dispensing process naturally collapse to form an arcuate surface. The cross section of the base layer  420   b  of  FIG. 17A  is a quadrilateral section formed by vertical cutting. The cross section of the base layer  420   b  of  FIG. 17B  is a trapezoidal and has slant edges Sc because the base layer  420   b  is cut bias or is cut by a cutter with an angular configuration. The base layer  420   b  of  FIG. 17C  is similar to that of  FIG. 17A , but the two corners located below away the top layer  420   a  are chamfered in a circular arc Se. Based upon different manufacturing process manners of the above-mentioned about  FIGS. 17A to 17C , when the LED chip in the filament is illuminated, the LED filament as a whole can achieve different light emitting angles and light emitting performances. The base layer  420   b  of  FIG. 17D  is similar to the base layer  420   b  of  FIG. 17B , but the beveled side Sc of the base layer  420   b  in  FIG. 17D  is aligned with the side of the top layer  420   a  in a straight line, and the cross section of the top layer  420   a  is consisted of the arc portion and the oblique portion. In other words, the top layer  420   a  of  FIG. 17D  has a beveled side as extending from the beveled side Sc of the base layer  420   b , and the two beveled sides of the top layer  420   a  and the base layer  420   b  are symmetrically formed on opposite sides of the LED filament. The beveled side of the top layer  420   a  aligns with the beveled side Sc of the base layer  420   b . In this situation, the cross section of the top layer  420   a  in  FIG. 17D  will have an outer contour composed of an arched boundary and two opposite beveled sides Sc. In the process of the LED filament manufacturing, the LED chip is completed the die bonding on the surface of the large-area base layer  420   a , the top layer  420   a  is unitary coated on the upper surface of the large-area base layer  420   a , and then performs the cutting process of the LED filament to form the strip LED filament, thereby forming the top layer  420   a  and the base layer  420   b  shown in  FIG. 17D  having the same slope of the bevel sides and both beveled sides of the top and base layers are aligned with a straight line to form a common beveled side Sc. 
       FIG. 17E  is a schematic view showing the arrangement of the LED chip  442  inside the  FIG. 17A . The thickness and diameter of the base layer  420   b  may be smaller than that of the top layer  420   a . As shown in  FIG. 17E , the thickness T2 of the base layer  420   b  is smaller than the thickness T1 of the top layer  420   a , and the thickness of the base layer  420   b  or the top layer  420   a  may be uneven due to the process, therefore, the T1 and T2 represent the maximum thickness of the top layer  420   a  and the base layer  420   b , respectively. Besides, the LED chip  442  is placed on the surface of the base layer  420   b  and wrapped in the top layer  420   a . In some aspects, the conductive electrode of an LED filament (not shown) may be disposed primarily in the base layer  420   b . In the case when the thickness of the base layer  420   b  is thinner than that of the top layer  420   a , the heat generated from the LED filament conductive electrode can be more easily dissipated from the base layer  420   b . In some aspects, the major emitting direction of the LED chip  442  is to face the top layer  420   a , so that the most of light emitting from the LED chip  442  will penetrate the top layer  420   a , which causes the base layer  420   b  to have a relative lower brightness than the top layer  420   a . In one embodiment, the top layer  420   a  has a relatively large amount of light reflecting and/or diffusing particles, for example phosphor particles, which can reflect or diffuse the light toward the base layer  420   b , and the light can easily penetrate the thinner base layer  420   b , thereby achieving uniform brightness of the top layer  420   a  and the base layer  420   b . In another embodiment, when the top layer  420   a  and the base layer  420   b  have the same thickness, the phosphor particle concentration of the top layer  420   a  can be configured to be greater than the phosphor particle concentration of the base layer  420   b , so that the color temperature of the LED filament is more uniform. 
     Referring to  FIGS. 17E and 17F , W1 is the width of the base layer  420   b  or the top layer  420   a , and W2 is the width of the LED chip  442 . When the width of the base layer  420   b  or the top layer  420   a  is not uniform, W1 represents the width of the upper surface of the base layer  420   b  or the width of the lower surface of the top layer  420   a , the proportion of W1 and W2 is W1:W2=1:(0.8 to 0.9). The upper surface of the base layer  420   b  contacts the LED chip  402 , and the lower surface thereof is away from the LED chip  442  and opposite to the upper surface of the base layer  420   b , in contrast, the upper surface of the top layer  420   b  is away from the LED chip  442 , and the lower surface thereof is opposite to the upper surface of the top layer  420   b  and contacts the base layer  420   a . In  FIG. 17E , W1 indicates the width of the upper surface of the base layer  420   b  or the minimum width of the base layer  420   b .  FIG. 17F  is a schematic view showing the arrangement of the LED chip  402  inside the  FIG. 17B , and W1 is the width of the lower surface of the top layer  420   b  or the maximum width of the top layer  420   a . In an embodiment such as the top layer  420   a  and the base layer  420   b  of  FIG. 17D  have a common beveled side Sc, W1 is the width of the lower surface of the top layer  420   a  or the maximum width of the base layer  420   b . The LED chip  442  is a six faced illuminator, in order to ensure lateral illuminating of the LED filament, that is lateral faces of the LED chip  442  are still covered by the top layer  402   a , the widths W1 and W2 can be designed to be unequal and the width W1 is greater than the width of W2. On the other hand, in order to ensure that the LED filament has a certain flexibility and can be bent with a small curvature radius, in other words, for making sure that the filament retains a certain degree of flexibility, therefore, the ratio of the thickness and the width of the cross section of the LED filament which is perpendicular to the longitudinal direction of the LED filament is ideally tended to be consistent. With this design, the LED filament can be easily realized with an omni-directional light effect and has a better bending property. 
     When the LED filament is illuminated in an LED light bulb encapsulation with the inert gas, as shown in  FIG. 18 , the light emitted by the LED chip  442  passes through the interfaces A, B, C, D, E and F respectively, wherein the interface A is the interface between the p-GaN gate and the top layer  420   a  in the LED chip  442 . The interface B is the interface between the top layer  420   a  and the inert gas, the interface C is the interface between the substrate and the paste  450  (e.g., die bond paste) in the LED chip  442 , the D interface is the interface between the paste  450  and the base layer  420   b , the interface E is the interface between the base layer  420   b  and the inert gas, and the interface F is the interface between the base layer  420   b  and the top layer  420   a . When light passes through the interfaces A, B, C, D, E and F respectively, the refractive index of the two substances in any interface is n1 and n2 respectively, then |n1−n2|&lt;1.0, preferably |n1−n2|&lt;0.5, more preferably |n1−n2|&lt;0.2. In one embodiment, the refractive index of two substances in any one of the four interfaces of B, E, D and F is n1 and n2 respectively, and then |n1−n2|&lt;1.0, preferably |n1−n2|&lt;0.5, More preferably |n1−n2|&lt;0.2. In one embodiment, the refractive index of two substances in any interface of D and F two interfaces is n1 and n2 respectively, then |n1−n2|&lt;1.0, preferably |n1−n2|&lt;0.5, preferably |n1−n2|&lt;0.2. The absolute value of the difference in refractive index of the two substances in each interface is smaller, the light emitting efficiency is higher. For example, when the light emitted by the LED chip  442  passes from the base layer  420   b  to the top layer  420   a , the incident angle is θ1, the refraction angle is θ2, and the refractive index of the base layer  420   b  is n1, and the refractive index of the top layer  420   a  is n2, according to the equation sin θ1/sin θ2=n2/n1, when the absolute value of the difference between n1 and n2 is smaller, the incident angle closer to the refraction angle, and then the light-emitting efficiency of the LED filament is higher. 
     Referring to  FIG. 19A ,  FIG. 19A  shows the cross sectional view of a portion of the LED filament  400  in the longitudinal direction of the LED filament  400 ,  FIG. 19A  shows three LED filament units  400   a   1  and each LED filament unit  400   a   1  includes a single LED chip  442 .  FIG. 19B  is a cross sectional view of the LED filament unit  400   a   1  in the short axial direction of the LED filament. As shown in  FIGS. 19A and 19B , the illumination angle of the LED chip  442  in the longitudinal direction of the LED filament is α, the illumination angle of the LED chip  442  in the short axial direction of the LED filament is β, and the surface of the LED chip  442  away from the base layer  420   b  is defined by the upper surface of the LED chip  442 , the distance from the upper surface of the LED chip  442  to the outer surface of the top layer is H, and the length of the LED filament unit  400   a   1  in the longitudinal direction of the LED filament is C, and the light emitting area of an LED chip  442  in the LED filament in the longitudinal direction of the LED filament is the illumination coverage of the illumination angle α, the LED chip emits the light along with the illumination angle α and it projects on the outer surface of the top layer  420   a  with a length of the linear distance L1. The light emitting area of an LED chip  442  in the LED filament in the short axial direction of the LED filament is the illumination coverage of the illumination angle β, the LED chip emits the light along with the illumination angle β and it projects on the outer surface of the top layer  420   a  with a length of the linear distance L2. It is considered that the LED filament has ideal light emitting area, better bending property, thermal dissipation performance, avoiding to occur obvious dark areas of LED filament and reducing material waste, etc. at the same time, the L1 value can be designed by the equation as 0.5C≤L1≤10C, preferably C≤L1≤2C. Further, under the equation L2≥W1, if the L1 value is smaller than the C value, the light emitting areas of the adjacent LED chips  442  in the longitudinal direction cannot be intersected, therefore the LED filament may have a dark area in the longitudinal direction. Moreover, when the L2 value is smaller than the W1 value, it represents the width of the LED chip  442  in the short axial direction of the filament is too large, and it is also possible to cause the top layer  420   a  having dark areas on both sides in the short axial direction. The dark areas not only affect the overall light illumination efficiency of the LED filament, but also indirectly cause waste of material use. The specific values of α, β depend on the type or specification of the LED chip  442 . 
     In one embodiment, in the longitudinal direction of the LED filament:
 
 H=L ½ tan 0.5α,0.5 C≤L 1≤10 C , then 0.5 C/ 2 tan 0.5α≤ H≤ 10 C/ 2 tan 0.5α;
 
     in the short axial direction of the LED:
 
 H=L 2/2 tan 0.5β, L 2≥ W 1, then  H≥W ½ tan 0.5β;
 
     therefore, Hmax=10C/2 tan 0.5α, Hmin=a; setting a is the maximum value in both 0.5C/2 tan 0.5α and W½ tan 0.5β, and setting A is the maximum value in both C/2 tan 0.5α and W½ tan 0.5β. 
     Thus, the equation between the distance H and the setting value a and A respectively as a≤H≤10C/2 tan 0.5α, preferably A≤H≤2C/2 tan 0.5α. When the type of the LED chip  442 , the spacing between adjacent LED chips, and the width of the filament are known, the distance H from the light emitting surface of the LED chip  442  to the outer surface of the top layer can be determined, so that the LED filament has a superior light emitting area in both the short axial and longitudinal direction of the LED filament. 
     Most LED chips have an illumination angle of 120° in both the short axial and longitudinal direction of the LED filament. The setting b is the maximum of 0.14C and 0.28W1, and B is the maximum of 0.28C and 0.28W1, then the equation between the distance H and the setting value b and B respectively as b≤H≤2.9 C and preferably B≤H≤0.58 C. 
     In one embodiment, in the longitudinal direction of the LED filament:
 
 H=L ½ tan 0.5α,0.5 C≤L 1≤10 C;  
 
     in the short axial direction of the LED filament:
 
 H=L 2/2 tan 0.5β, L 2≥ W 1; then  W 1≤2 H  tan 0.5β;
 
then 0.5 C  tan 0.5β/tan 0.5α≤ L 2≤10 C  tan 0.5β/tan 0.5α, L 2≥ W 1;
 
therefore,  W 1≤10 C  tan 0.5β/tan 0.5α, thus  W 1 max=min(10 C  tan 0.5β/tan 0.5α,2 H  tan 0.5β).
 
     The relationship between the LED chip width W2 and the base layer width W1 is set to W1:W2=1:0.8 to 0.9, so that the minimum of W1 as W1 min=W2/0.9 can be known. 
     Setting d is the minimum of 10C tan 0.5β/tan 0.5α and 2H tan 0.5β, and D is the minimum of 2C tan 0.5β/tan 0.5α and 2H tan 0.5β, then the equation between the base layer width W1, the LED chip width W2, and the setting value d and D respectively is W2/0.9≤W1≤d, preferably W2/0.9≤W1≤D. 
     When the type of the LED chip  442 , the distance between the adjacent two LED chips in the LED filament, and the H value are known, the range of the width W of the LED filament can be calculated, so that the LED filament can be ensured in the short axial direction and the longitudinal direction of the LED filament both have superior light emitting areas. 
     Most of the LED chips have an illumination angle of 120° in the short axial and in the longitudinal direction of the LED filament, the e is set to a minimum value of 10C and 3.46H, and the E is set to a minimum value of 2C and 3.46H, in the case the equation between the width W1, W2 and the setting value e and E respectively as 1.1W2≤W1≤e, preferably 1.1W2≤W1≤E. 
     In one embodiment, in the longitudinal direction of the LED filament:
 
 H=L ½ tan 0.5α,0.5 C≤L 1≤10 C , then 0.2 H  tan 0.5α≤ C≤H  tan 0.5α;
 
     in the short axial direction of the LED filament:
 
 H=L 2/2 tan 0.5β, L 2≥ W 1, then  L 1≥ W 1 tan 0.5α/tan 0.5β;
 
thus  W 1 tan 0.5α/tan 0.5β≤10 C , and  C≥ 0.1 W 1 tan 0.5α/tan 0.5β;
 
then  C  max=4 H  tan 0.5α.
 
     Setting f is the maximum value of both 0.2H tan 0.5α and 0.1W1 tan 0.5α/tan 0.5β, and setting F is the maximum value of both H tan 0.5α and 0.1W1 tan 0.5α/tan 0.5β, therefore f≤C≤4H tan 0.5α, preferably F≤C≤2H tan 0.5α. 
     When the width W, the H value, and type of the LED chip  442  of the LED filament are determined, the range of the width C of the LED filament can be known, so that the LED filament has superior light emitting area in both the short axial direction and the longitudinal direction of the LED filament. 
     Most LED chips have an illumination angle of 120° in the short axial direction and in the longitudinal direction of the LED filament of the LED filament. The setting g is the maximum value of 0.34H and 0.1W1, and setting G is the maximum value of 1.73H and 0.1W1, thereby the equation between the value C, H and the setting value g and G respectively as g≤C≤6.92H, preferably G≤C≤3.46H. 
     In the above embodiment, since the thickness of the LED chip  442  is small relative to the thickness of the top layer  420   a , it is negligible in most cases, that is, the H value may also represent the actual thickness of the top layer  420   a . In one embodiment, the height of any of the two top layers  420   a  as shown in  FIG. 7  also applies to the range of the H value as aforementioned equation. In another embodiment, the difference from  FIG. 7  is that the LED chip  442  and the conductive electrodes  410  and  412  are disposed on one surface of the base layer  420   b , and the LED chip  442  and the conductive electrodes  410  and  412  are not disposed on the other surface opposite to the surface, in this case, the height of the top layer  420   a  applies to the range of the H value as aforementioned equation. In other embodiments, the light conversion layer is similar to the structure of the light conversion layer  420  as shown in  FIG. 6A  and  FIG. 7 , for example, only the position of the conductive electrode shown in  FIG. 6A  and  FIG. 7  is different, and the height of the top layer  420   a  is suitable for the range of the H value as aforementioned equation. 
     Referring to  FIGS. 20A and 20B ,  FIGS. 20A and 20B  are cross sectional views of the LED filament unit  400   a   1  having different thickness of the top layers  420   a , and the surface of the LED chip  442  opposite to the interface between the LED chip  442  and the base layer  420   b  is referred to as light emitting surface Ca. In one embodiment, as shown in  FIG. 20A , the shape of the top layer  420   a  is a semicircle with different diameters, for example the dashed line illustrated another diameter, and the center o of the top layer  420   a  does not located on the light emitting surface Ca of the LED chip  442 , further, the distance that the emitting light projected onto the circumference of the outer surface of the top layer  420   a  is r1, r2, respectively. When the light emitting traverses the interface B, that is the interface between the top layer and the inert gas, the incident angles formed at the interfaces of the radii r1 and r2 of the top layer  420   a  are α, β, respectively. It can be known from the equation tan α=m/r1 and tan β=m/r2 that the radius is larger, the incident angle is smaller, and the light emitting efficiency of the LED filament is higher. That is to say, when the top layer  420   a  has a semicircular shape, the maximum radius/diameter value should be taken as much as possible to obtain a better light emitting efficiency. In another embodiment, as shown in  FIG. 20B , a top layer  420   a  has a semicircular shape, and the other top layer  420   a  has an elliptical shape, wherein the major axis of the ellipse has the same length as the diameter of the semicircular shape, and the center point o of the top layer  420   a  and the center point o of the ellipse do not overlap with the light emitting surface Ca of the LED chip  442 . As shown in  FIG. 20B , when the emitted light passes through the interface B in the same direction, the distances of the emitting light on the circumference and the elliptical arc are r1 and r2 respectively, and the incident angles are α and β, respectively, from the equations tan α=m/r1 and tan β=m/r2, it can be seen that the larger the r1 and r2, the smaller the incident angle, the higher the light emitting efficiency of the LED filament. In other words, in compared to the elliptical shape, the cross section of the top layer  420   a  in the shape of semicircular has better light emitting efficiency, that is, the distance from the center point of the LED chip to the outer surface of the top layer is substantially the same. As shown in  FIG. 20C , the center O of the top layer  420   a  indicated by the solid line does not overlap with the light emitting surface Ca of the LED chip, and the center O′ of the top layer  420   a  indicated by the dashed line overlaps with the light emitting surface of the LED chip, and the radius of the semicircle with the center of O and the radius of the semicircle of O′ is equal. As shown in the figure, tan α=m1/r and tan β=m2/r, m1 is greater than m2, and thus α is greater than β, so that when the light emitting surface overlaps with the center of the top layer  420   a , that is the distance from the center point to the outer surface of the top layer is substantially the same, the light emitting efficiency is better. 
     The LED chip used in the aforementioned embodiments can be replaced by a back plated chip, and the plated metal is silver or gold alloy. When the back plated chip is used, the specular reflection can be enhanced, and the luminous flux of the light emitted from the light emitting surface A of the LED chip can be increased. 
     Next, a chip bonding design relating to an LED filament will be described. The  FIG. 21A  is a top view of an embodiment of the LED filament  300  in an unbent state in accordance with the present invention. The LED filament  300  includes a plurality of LED chip units  302 ,  304 , a conductor  330   a , and at least two conductive electrodes  310 ,  312 . The LED chip units  302  and  304  may be a single LED chip, or may include a plurality of LED chips, that is, equal to or greater than two LED chips. 
     The conductor  330   a  is located between the adjacent two LED chip units  302 ,  304 , the LED chip units  302 ,  304  are at different positions in the Y direction, and the conductive electrodes  310 ,  312  are disposed corresponding to the LED chip units  302 ,  304  and electrically connected to the LED chip units  302  and  304  through the wires  340 . The adjacent two LED chip units  302  and  304  are electrically connected to each other through the conductor  330   a . The angle between the conductor  330   a  and the LED filament in the longitudinal direction (X direction) is 30° to 120°, preferably 60° to 120°. In the related art, the direction of the conductor  330   a  is parallel to the X direction, and the internal stress acting on the cross sectional area of the conductor is large when the filament is bent at the conductor. Therefore, the conductor  330   a  is disposed at a certain angle with the X direction and it can effectively reduce the internal stress thereof. The wire  340  is at an angle, parallel, vertical or any combination with the X direction. In the embodiment, the LED filament  300  includes two wires  340 , one wire  340  is parallel to the X direction, and the other wire  340  has an angle of 30° to 120° with respect to the X direction. The LED filament  300  emits light after its conductive electrodes  310 ,  312  are powered with voltage source or current source. 
       FIGS. 21B to 21D  show the case where the conductor  330   a  is 90° with respect to the X direction, that is, the conductor  330   a  is perpendicular to the X direction, which can reduce the internal stress on the conductor cross sectional area when the filament is bent. In some embodiment the wire  340  both in parallel and vertically with respect to the X direction are combined in an LED filament, as shown in  FIG. 21B , the LED filament  300  includes two wires  340 , one wire  340  being parallel to the X direction and the other wire  340  being perpendicular to the X direction. 
     As shown in  FIG. 21C , the difference from the embodiment shown in  FIG. 21B  is that the wire  340  is perpendicular to the X direction, and the bendability duration between the conductive electrodes  310 ,  312  and the LED chip units  302 ,  304  is improved. Further, since the conductor  330   a  and the wire  340  are simultaneously arranged to be perpendicular to the X direction, the LED filament can have good bendability at any position. 
       FIG. 21E  is a top view of the LED filament  300  in an unbent state in accordance with one embodiment of the present invention.  FIG. 21E  differs from the embodiment shown in  FIG. 21C  is that, in the X direction, the LED chip unit  304  is between two adjacent LED chip units  302 , and no overlap with the LED chip unit  302  in the projection in the Y direction, so that when the LED filament is bent at the conductor  330   a , the LED chip is not damaged, thereby improving the stability of the LED light bulb product quality. 
     As shown in  FIG. 21F , the LED filament  300  includes a plurality of LED chip units  302 ,  304 , a conductor  330   a , and at least two conductive electrodes  310 ,  312 . The conductor  330   a  is located between adjacent LED chip units  302 ,  304 , and the LED chip units  302 ,  304  are disposed at substantially the same position in the Y direction, so that the overall width of the LED filament  300  is smaller, thereby shortening the thermal dissipation path of the LED chip and improving the thermal dissipation effect. The conductive electrodes  310 ,  312  are correspondingly arranged to the LED chip units  302 ,  304 , and are electrically connected to the LED chip units  302 ,  304  through the wires  340 . The LED chip units  302 / 304  are electrically connected to the conductors  330   a  through the wires  350 , and the conductors  330   a  are in the font shape like deformed Z letter. The aforesaid shape can increase the mechanical strength of the region where the conductor and the LED chip are located in, and can avoid the damage of the wire connecting the LED chip and the conductor when the LED filament  300  is bent. At the same time, the wire  340  is disposed in a parallel with the X direction. 
     As shown in  FIG. 21G , the LED filament  300  includes a plurality of LED chip units  302 ,  304 , at least one conductor  330   a , and at least two conductive electrodes  310 ,  312 . The LED chip units  302 ,  304  are in the same position in the Y direction, and the conductor  330   a  parallel to the X direction, the conductor  330   a  includes a first conductor  3301   a  and a second conductor  3302   a , respectively located on opposite sides of the LED chip unit  302 / 304 , and the first conductor  3301   a  is located between adjacent LED chip units  302 ,  304  and electrically connected to the LED chip unit  302 / 304  through the wire  350 . The wire  350  is perpendicular to the X direction, and reduces the internal stress on the cross sectional area of the wire when the LED filament  300  is bent, thereby improving the bendability of the wire. The second conductor  3302   a  is not electrically connected to the LED chip units  302 ,  304 , and the second conductor  3302   a  extends along the X direction to the one end of each wire  340  adjacent to the electrode. When the LED filament  300  is suffered external force, it can play the role of stress buffering, protect the LED chip, improve product stability, and secondly make the force balance on both sides of the LED chip. The conductive electrodes  310 ,  312  are configured corresponding to the LED chip units  302 ,  304 , and are electrically connected to the LED chip units  302 ,  304  through wires  340 . 
     As shown in  FIG. 21H , the difference from the embodiment shown in FIG.  21 G is that the first conductor  3301   a  and the second conductor  3302   a  extends along the X direction to the one end of each wire  340  adjacent to the electrode, and the first conductor  3301   a  and the second conductor  3302   a  are electrically connected to both the LED chip unit  302  and the LED chip unit  304  by wires  350 . In other embodiments, for example, the first conductor  3301   a  is electrically connected to the LED chip unit  302  and the LED chip unit  304  through the wire  350 , and the second conductor  3302   a  may not be electrically connected to the LED chip unit  302 / 304 . By setting conductors on both sides of the LED chip, when the LED filament  300  is bent, it can not only increase the strength of the LED filament  300  but also disperse the heat generated by the LED chips during illumination. 
       FIG. 21I  is a top view showing an embodiment of the LED filament  300  in an unbent state. In the present embodiment, the LED chip units  302  and  304  are single LED chips, and the width of the LED chip units  302  and  304  is parallel to the X direction. Preferably, the LED chip units  302  and  304  are at substantially the same position in the Y direction, so that the overall width of the LED filament  300  is smaller, thereby shortening the heat dissipation path of the LED chip and improving the thermal dissipation effect. The adjacent two LED chip units  302  and  304  are connected by a conductor  330   a , and the angle between the conductor  330   a  and the X direction is 30° to 120°, which reduces the internal stress on the cross sectional area of the wire and also improves the bendability of the wire when the LED filament  300  is bent. In other embodiments, the LED chip unit longitudinally may have an angle with the X direction as the conductor  330   a , which may further reduce the overall width of the LED filament  300 . 
       FIG. 22A  is a schematic view showing an embodiment of a layered structure of the LED filament  400  of the present invention. The LED filament  400  has a light conversion layer  420 , two LED chip units  402 ,  404 , two conductive electrodes  410 ,  412 , and a conductive section  430  for electrically connecting adjacent two LED chip units  402 ,  404 . Each of the LED chip units  402 ,  404  includes at least two LED chips  442  that are electrically connected to each other by wires  440 . In the present embodiment, the conductive section  430  includes a conductor  430 , and the conductive section  430  is electrically connected to the LED sections  402 ,  404  through the wires  450 . The shortest distance between the two LED chips  442  located in the adjacent two LED chip units  402 ,  404  is greater than the distance between adjacent two LED chips in the same chip unit  402 / 404 . Moreover, the length of wire  440  is less than the length of conductor  430   a . The light conversion layer  420  is disposed on the LED chip  442  and at least two sides of the conductive electrodes  410 ,  412 . The light conversion layer  420  exposes a portion of the conductive electrodes  410 ,  412 . The light conversion layer  420  may composed of at least one top layer  420   a  and one base layer  420   b  as the upper layer and the lower layer of the LED filament respectively. In the present embodiment, the LED chips  442  and the conductive electrodes  410 ,  412  are sandwiched in between the top layer  420   a  and the base layer  420   b . When the wire bonding process of the face up chip is carried out along the x direction, for example, the bonding wire and the bonding conductor are gold wires, the quality of the bonding wire is mainly determined by the stress at the five points A, B, C, D, and E as shown in  FIG. 22B . The point A is the junction of the soldering pad  4401  and the gold ball  4403 , point B is the junction of the gold ball  4403  and the gold wire  440 , point C is between the two segments of the gold wire  440 , point D is the gold wire  440  and the two solder butted joints  4402 , and the point E is between the two solder butted joints  4402  and the surface of the chip  442 . Because of point B is the first bending point of the gold wire  440 , and the gold wire  440  at the point D is thinner, thus gold wire  440  is frangible at points B and D. So that, for example, in the implementation of the structure of the LED filament  300  package showing in  FIG. 22A , the top layer  420   a  only needs to cover points B and D, and a portion of the gold wire  440  is exposed outside the light conversion layer. If the one of the six faces of the LED chip  442  farthest from the base layer  420   b  is defined as the upper surface of the LED chip  442 , the distance from the upper surface of the LED chip  442  to the surface of the top layer  420   a  is in a range of around 100 to 200 μm. 
     The next part will describe the material of the filament of the present invention. The material suitable for manufacturing a filament substrate or a light-conversion layer for LED should have properties such as excellent light transmission, good heat resistance, excellent thermal conductivity, appropriate refraction rate, excellent mechanical properties and good warpage resistance. All the above properties can be achieved by adjusting the type and the content of the main material, the modifier and the additive contained in the organosilicon-modified polyimide composition. The present disclosure provides a filament substrate or a light-conversion layer formed from a composition comprising an organosilicon-modified polyimide. The composition can meet the requirements on the above properties. In addition, the type and the content of one or more of the main material, the modifier (thermal curing agent) and the additive in the composition can be modified to adjust the properties of the filament substrate or the light-conversion layer, so as to meet special environmental requirements. The modification of each property is described herein below. 
     Adjustment of the Organosilicon-Modified Polyimide 
     The organosilicon-modified polyimide provided herein comprises a repeating unit represented by the following general Formula (I): 
     
       
         
         
             
             
         
       
     
     In general Formula (I), Ar 1  is a tetra-valent organic group. The organic group has a benzene ring or an alicyclic hydrocarbon structure. The alicyclic hydrocarbon structure may be monocyclic alicyclic hydrocarbon structure or a bridged-ring alicyclic hydrocarbon structure, which may be a dicyclic alicyclic hydrocarbon structure or a tricyclic alicyclic hydrocarbon structure. The organic group may also be a benzene ring or an alicyclic hydrocarbon structure comprising a functional group having active hydrogen, wherein the functional group having active hydrogen is one or more of hydroxyl, amino, carboxy, amido and mercapto. 
     Ar 2  is a di-valent organic group, which organic group may have for example a monocyclic alicyclic hydrocarbon structure or a di-valent organic group comprising a functional group having active hydrogen, wherein the functional group having active hydrogen is one or more of hydroxyl, amino, carboxy, amido and mercapto. 
     R is each independently methyl or phenyl. 
     n is 1˜5, preferably 1, 2, 3 or 5. 
     The polymer of general Formula (I) has a number average molecular weight of 5000˜100000, preferably 10000˜60000, more preferably 20000˜40000. The number average molecular weight is determined by gel permeation chromatography (GPC) and calculated based on a calibration curve obtained by using standard polystyrene. When the number average molecular weight is below 5000, a good mechanical property is hard to be obtained after curing, especially the elongation tends to decrease. On the other hand, when it exceeds 100000, the viscosity becomes too high and the resin is hard to be formed. 
     Ar 1  is a component derived from a dianhydride, which may be an aromatic anhydride or an aliphatic anhydride. The aromatic anhydride includes an aromatic anhydride comprising only a benzene ring, a fluorinated aromatic anhydride, an aromatic anhydride comprising amido group, an aromatic anhydride comprising ester group, an aromatic anhydride comprising ether group, an aromatic anhydride comprising sulfide group, an aromatic anhydride comprising sulfonyl group, and an aromatic anhydride comprising carbonyl group. 
     Examples of the aromatic anhydride comprising only a benzene ring include pyromellitic dianhydride (PMDA), 2,3,3′,4′-biphenyl tetracarboxylic dianhydride (aBPDA), 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (sBPDA), and 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydro naphthalene-1,2-dicarboxylic anhydride (TDA). Examples of the fluorinated aromatic anhydride include 4,4′-(hexafluoroisopropylidene)diphthalic anhydride which is referred to as 6FDA. Examples of the aromatic anhydride comprising amido group include N,N′-(5,5′-(perfluoropropane-2,2-diyl)bis(2-hydroxy-5,1-phenylene))bis(1,3-dioxo-1,3-dihydroisobenzofuran)-5-arboxamide) (6FAP-ATA), and N,N′-(9H-fluoren-9-ylidenedi-4,1-phenylene)bis[1,3-dihydro-1,3-dioxo-5-isobenzofuran carboxamide] (FDA-ATA). Examples of the aromatic anhydride comprising ester group include p-phenylene bis(trimellitate) dianhydride (TAHQ). Examples of the aromatic anhydride comprising ether group include 4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA), 4,4′-oxydiphthalic dianhydride (sODPA), 2,3,3′,4′-diphenyl ether tetracarboxylic dianhydride (aODPA), and 4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride)(BPADA). Examples of the aromatic anhydride comprising sulfide group include 4,4′-bis(phthalic anhydride)sulfide (TPDA). Examples of the aromatic anhydride comprising sulfonyl group include 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA). Examples of the aromatic anhydride comprising carbonyl group include 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA). 
     The alicyclic anhydride includes 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride which is referred to as HPMDA, 1,2,3,4-butanetetracarboxylic dianhydride (BDA), tetrahydro-1H-5,9-methanopyrano[3,4-d]oxepine-1,3,6,8(4H)-tetrone (TCA), hexahydro-4,8-ethano-1H,3H-benzo [1,2-C:4,5-C′]difuran-1,3,5,7-tetrone (BODA), cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA), and 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CpDA); or alicyclic anhydride comprising an olefin structure, such as bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (COeDA). When an anhydride comprising ethynyl such as 4,4′-(ethyne-1,2-diyl)diphthalic anhydride (EBPA) is used, the mechanical strength of the light-conversion layer can be further ensured by post-curing. 
     Considering the solubility, 4,4′-oxydiphthalic anhydride (sODPA), 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), cyclobutanetetracarboxylic dianhydride (CBDA) and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) are preferred. The above dianhydride can be used alone or in combination. 
     Ar 2  is derived from diamine which may be an aromatic diamine or an aliphatic diamine. The aromatic diamine includes an aromatic diamine comprising only a benzene ring, a fluorinated aromatic diamine, an aromatic diamine comprising ester group, an aromatic diamine comprising ether group, an aromatic diamine comprising amido group, an aromatic diamine comprising carbonyl group, an aromatic diamine comprising hydroxyl group, an aromatic diamine comprising carboxy group, an aromatic diamine comprising sulfonyl group, and an aromatic diamine comprising sulfide group. 
     The aromatic diamine comprising only a benzene ring includes m-phenylenediamine, p-phenylenediamine, 2,4-diaminotoluene, 2,6-diamino-3,5-diethyltoluene, 3,3′-dimethylbiphenyl-4,4′-diamine 9,9-bis(4-aminophenyl)fluorene (FDA), 9,9-bis(4-amino-3-methylphenyl)fluorene, 2,2-bis(4-aminophenyl)propane, 2,2-bis(3-methyl-4-aminophenyl)propane, 4,4′-diamino-2,2′-dimethylbiphenyl(APB). The fluorinated aromatic diamine includes 2,2′-bis(trifluoromethyl)benzidine (TFMB), 2,2-bis(4-aminophenyl)hexafluoropropane (6FDAM), 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP), and 2,2-bis(3-amino-4-methylphenyl)hexafluoropropane (BIS-AF-AF). The aromatic diamine comprising ester group includes [4-(4-aminobenzoyl)oxyphenyl]4-aminobenzoate (ABHQ), bis(4-aminophenyl)terephthalate (BPTP), and 4-aminophenyl 4-aminobenzoate (APAB). The aromatic diamine comprising ether group includes 2,2-bis[4-(4-aminophenoxy)phenyl]propane)(BAPP), 2,2′-bis[4-(4-aminophenoxy)phenyl]propane (ET-BDM), 2,7-bis(4-aminophenoxy)-naphthalene (ET-2,7-Na), 1,3-bis(3-aminophenoxy)benzene (TPE-M), 4,4′[1,4-phenyldi(oxy)]bis[3-(trifluoromethyl)aniline] (p-6FAPB), 3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether (ODA), 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,4-bis(4-aminophenoxy)benzene (TPE-Q), and 4,4′-bis(4-aminophenoxy)biphenyl(BAPB). The aromatic diamine comprising amido group includes N,N′-bis(4-aminophenyl)benzene-1,4-dicarboxamide (BPTPA), 3,4′-diamino benzanilide (m-APABA), and 4,4′-diaminobenzanilide (DABA). The aromatic diamine comprising carbonyl group includes 4,4′-diaminobenzophenone (4,4′-DABP), and bis(4-amino-3-carboxyphenyl) methane (or referred to as 6,6′-diamino-3,3′-methylanediyl-dibenzoic acid). The aromatic diamine comprising hydroxyl group includes 3,3′-dihydroxybenzidine (HAB), and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP). The aromatic diamine comprising carboxy group includes 6,6′-diamino-3,3′-methylanediyl-dibenzoic acid (MBAA), and 3,5-diaminobenzoic acid (DBA). The aromatic diamine comprising sulfonyl group includes 3,3′-diaminodiphenyl sulfone (DDS), 4,4′-diaminodiphenyl sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS) (or referred to as 4,4′-bis(4-aminophenoxy)diphenylsulfone), and 3,3′-diamino-4,4′-dihydroxydiphenyl sulfone (ABPS). The aromatic diamine comprising sulfide group includes 4,4′-diaminodiphenyl sulfide. 
     The aliphatic diamine is a diamine which does not comprise any aromatic structure (e.g., benzene ring). The aliphatic diamine includes monocyclic alicyclic amine and straight chain aliphatic diamine, wherein the straight chain aliphatic diamine include siloxane diamine, straight chain alkyl diamine and straight chain aliphatic diamine comprising ether group. The monocyclic alicyclic diamine includes 4,4′-diaminodicyclohexylmethane (PACM), and 3,3′-dimethyl-4,4-diaminodicyclohexylmethane (DMDC). The siloxane diamine (or referred to as amino-modified silicone) includes α,ω-(3-aminopropyl)polysiloxane (KF8010), X22-161A, X22-161B, NH15D, and 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (PAME). The straight chain alkyl diamine has 6˜12 carbon atoms, and is preferably un-substituted straight chain alkyl diamine. The straight chain aliphatic diamine comprising ether group includes ethylene glycol di(3-aminopropyl) ether. 
     The diamine can also be a diamine comprising fluorenyl group. The fluorenyl group has a bulky free volume and rigid fused-ring structure, which renders the polyimide good heat resistance, thermal and oxidation stabilities, mechanical properties, optical transparency and good solubility in organic solvents. The diamine comprising fluorenyl group, such as 9,9-bis(3,5-difluoro-4-aminophenyl)fluorene, may be obtained through a reaction between 9-fluorenone and 2,6-dichloroaniline. The fluorinated diamine can be 1,4-bis(3′-amino-5′-trifluoromethylphenoxy)biphenyl, which is a meta-substituted fluorine-containing diamine having a rigid biphenyl structure. The meta-substituted structure can hinder the charge flow along the molecular chain and reduce the intermolecular conjugation, thereby reducing the absorption of visible lights. Using asymmetric diamine or anhydride can increase to some extent the transparency of the organosilicon-modified polyimide resin composition. The above diamines can be used alone or in combination. 
     Examples of diamines having active hydrogen include diamines comprising hydroxyl group, such as 3,3′-diamino-4,4′-dihydroxybiphenyl, 4,4′-diamino-3,3′-dihydroxy-1,1′-biphenyl (or referred to as 3,3′-dihydroxybenzidine) (HAB), 2,2-bis(3-amino-4-hydroxyphenyl)propane (BAP), 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP), 1,3-bis(3-hydro-4-aminophenoxy) benzene, 1,4-bis(3-hydroxy-4-aminophenyl)benzene and 3,3′-diamino-4,4′-dihydroxydiphenyl sulfone (ABPS). Examples of diamines comprising carboxy group include 3,5-diaminobenzoic acid, bis(4-amino-3-carboxyphenyl)methane (or referred to as 6,6′-diamino-3,3′-methylenedibenzoic acid), 3,5-bis(4-aminophenoxy)benzoic acid, and 1,3-bis(4-amino-2-carboxyphenoxy)benzene. Examples of diamines comprising amino group include 4,4′-diaminobenzanilide (DABA), 2-(4-aminophenyl)-5-aminobenzoimidazole, diethylenetriamine, 3,3′-diaminodipropylamine, triethylenetetramine, and N,N′-bis(3-aminopropyl)ethylenediamine (or referred to as N,N-di(3-aminopropyl)ethylethylamine). Examples of diamines comprising thiol group include 3,4-diaminobenzenethiol. The above diamines can be used alone or in combination. 
     The organosilicon-modified polyimide can be synthesized by well-known synthesis methods. For example, it can be prepared from a dianhydride and a diamine which are dissolved in an organic solvent and subjected to imidation in the presence of a catalyst. Examples of the catalyst include acetic anhydride/triethylamine, and valerolactone/pyridine. Preferably, removal of water produced in the azeotropic process in the imidation is promoted by using a dehydrant such as toluene. 
     Polyimide can also be obtained by carrying out an equilibrium reaction to give a poly (amic acid) which is heated to dehydrate. In other embodiments, the polyimide backbone may have a small amount of amic acid. For example, the ratio of amic acid to imide in the polyimide molecule may be 1˜3:100. Due to the interaction between amic acid and the epoxy resin, the substrate has superior properties. In other embodiments, a solid state material such as a thermal curing agent, inorganic heat dispersing particles and phosphor can also be added at the state of poly (amic acid) to give the substrate. In addition, solubilized polyimide can also be obtained by direct heating and dehydration after mixing of alicylic anhydride and diamine. Such solubilized polyimide, as an adhesive material, has a good light transmittance. In addition, it is liquid state per se; therefore, other solid materials (such as the inorganic heat dispersing particles and the phosphor) can be dispersed in the adhesive material more sufficiently. 
     In one embodiment for preparing the organosilicon-modified polyimide, the organosilicon-modified polyimide can be produced by dissolving the polyimide obtained by heating and dehydration after mixing a diamine and an anhydride and a siloxane diamine in a solvent. In another embodiment, the amidic acid, before converting to polyimide, is reacted with the siloxane diamine. 
     In addition, the polyimide compound may be obtained by dehydration and ring-closing and condensation polymerization from an anhydride and a diamine, such as an anhydride and a diamine in a molar ratio of 1:1. In one embodiment, 200 micromole (mmol) of 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 20 micromole (mmol) of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP), 50 micromole (mmol) of 2,2′-di(trifluoromethyl)diaminobiphenyl(TFMB) and 130 micromole (mmol) of aminopropyl-terminated poly(dimethylsiloxane) are used to give the PI synthesis solution. 
     The above methods can be used to produce amino-terminated polyimide compounds. However, other methods can be used to produce carboxy-terminated polyimide compounds. In addition, in the above reaction between anhydride and diamine, where the backbone of the anhydride comprises a carbon-carbon triple bond, the affinity of the carbon-carbon triple bond can promote the molecular structure. Alternatively, a diamine comprising vinyl siloxane structure can be used. 
     The molar ratio of dianhydride to diamine may be 1:1. The molar percentage of the diamine comprising a functional group having active hydrogen may be 5˜25% of the total amount of diamine. The temperature under which the polyimide is synthesized is preferably 80˜250° C., more preferably 100˜200° C. The reaction time may vary depending on the size of the batch. For example, the reaction time for obtaining 10˜30 g polyimide is 6˜10 hours. 
     The organosilicon-modified polyimide can be classified as fluorinated aromatic organosilicon-modified polyimides and aliphatic organosilicon-modified polyimides. The fluorinated aromatic organosilicon-modified polyimides are synthesized from siloxane-type diamine, aromatic diamine comprising fluoro (F) group (or referred to as fluorinated aromatic diamine) and aromatic dianhydride comprising fluoro (F) group (or referred to as fluorinated aromatic anhydride). The aliphatic organosilicon-modified polyimides are synthesized from dianhydride, siloxane-type diamine and at least one diamine not comprising aromatic structure (e.g., benzene ring) (or referred to as aliphatic diamine), or from diamine (one of which is siloxane-type diamine) and at least one dianhydride not comprising aromatic structure (e.g., benzene ring) (or referred to as aliphatic anhydride). The aliphatic organosilicon-modified polyimide includes semi-aliphatic organosilicon-modified polyimide and fully aliphatic organosilicon-modified polyimide. The fully aliphatic organosilicon-modified polyimide is synthesized from at least one aliphatic dianhydride, siloxane-type diamine and at least one aliphatic diamine. The raw materials for synthesizing the semi-aliphatic organosilicon-modified polyimide include at least one aliphatic dianhydride or aliphatic diamine. The raw materials required for synthesizing the organosilicon-modified polyimide and the siloxane content in the organosilicon-modified polyimide would have certain effects on transparency, chromism, mechanical property, warpage extent and refractivity of the substrate. 
     The organosilicon-modified polyimide of the present disclosure has a siloxane content of 20˜75 wt %, preferably 30˜70 wt %, and a glass transition temperature of below 150° C. The glass transition temperature (Tg) is determined on TMA-60 manufactured by Shimadzu Corporation after adding a thermal curing agent to the organosilicon-modified polyimide. The determination conditions include: load: 5 gram; heating rate: 10° C./min; determination environment: nitrogen atmosphere; nitrogen flow rate: 20 ml/min; temperature range: −40 to 300° C. When the siloxane content is below 20%, the film prepared from the organosilicon-modified polyimide resin composition may become very hard and brittle due to the filling of the phosphor and thermal conductive fillers, and tend to warp after drying and curing, and therefore has a low processability. In addition, its resistance to thermochromism becomes lower. On the other hand, when the siloxane content is above 75%, the film prepared from the organosilicon-modified polyimide resin composition becomes opaque, and has reduced transparency and tensile strength. Here, the siloxane content is the weight ratio of siloxane-type diamine (having a structure shown in Formula (A)) to the organosilicon-modified polyimide, wherein the weight of the organosilicon-modified polyimide is the total weight of the diamine and the dianhydride used for synthesizing the organosilicon-modified polyimide subtracted by the weight of water produced during the synthesis. 
     
       
         
         
             
             
         
       
     
     Wherein R is methyl or phenyl, preferably methyl, n is 1˜5, preferably 1, 2, 3 or 5. 
     The only requirements on the organic solvent used for synthesizing the organosilicon-modified polyimide are to dissolve the organosilicon-modified polyimide and to ensure the affinity (wettability) to the phosphor or the fillers to be added. However, excessive residue of the solvent in the product should be avoided. Normally, the number of moles of the solvent is equal to that of water produced by the reaction between diamine and anhydride. For example, 1 mol diamine reacts with 1 mol anhydride to give 1 mol water; then the amount of solvent is 1 mol. In addition, the organic solvent used has a boiling point of above 80° C. and below 300° C., more preferably above 120° C. and below 250° C., under standard atmospheric pressure. Since drying and curing under a lower temperature are needed after coating, if the temperature is lower than 120° C., good coating cannot be achieved due to high drying speed during the coating process. If the boiling point of the organic solvent is higher than 250° C., the drying under a lower temperature may be deferred. Specifically, the organic solvent may be an ether-type organic solvent, an ester-type organic solvent, a dimethyl ether-type organic solvent, a ketone-type organic solvent, an alcohol-type organic solvent, an aromatic hydrocarbon solvent or other solvents. The ether-type organic solvent includes ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, dipropylene glycol dimethyl ether or diethylene glycol dibutyl ether, and diethylene glycol butyl methyl ether. The ester-type organic solvent includes acetates, including ethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, propyl acetate, propylene glycol diacetate, butyl acetate, isobutyl acetate, 3-methoxybutyl acetate, 3-methyl-3-methoxybutyl acetate, benzyl acetate and 2-(2-butoxyethoxy)ethyl acetate; and methyl lactate, ethyl lactate, n-butyl acetate, methyl benzoate and ethyl benzoate. The dimethyl ether-type solvent includes triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether. The ketone-type solvent includes acetylacetone, methyl propyl ketone, methyl butyl ketone, methyl isobutyl ketone, cyclopentanone, and 2-heptanone. The alcohol-type solvent includes butanol, isobutanol, isopentanol, 4-methyl-2-pentanol, 3-methyl-2-butanol, 3-methyl-3-methoxybutanol, and diacetone alcohol. The aromatic hydrocarbon solvent includes toluene and xylene. Other solvents include γ-butyrolactone,N-methylpyrrolidone, N, N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide. 
     The present disclosure provides an organosilicon-modified polyimide resin composition comprising the above organosilicon-modified polyimide and a thermal curing agent, which may be epoxy resin, hydrogen isocyanate or bisoxazoline compound. In one embodiment, based on the weight of the organosilicon-modified polyimide, the amount of the thermal curing agent is 5˜12% of the weight of the organosilicon-modified polyimide. The organosilicon-modified polyimide resin composition may further comprise heat dispersing particles and phosphor. 
     Light Transmittance 
     The factors affecting the light transmittance of the organosilicon-modified polyimide resin composition at least include the type of the main material, the type of the modifier (thermal curing agent), the type and content of the heat dispersing particles, and the siloxane content. Light transmittance refers to the transmittance of the light near the main light-emitting wavelength range of the LED chip. For example, blue LED chip has a main light-emitting wavelength of around 450 nm, then the composition or the polyimide should have low enough or even no absorption to the light having a wavelength around 450 nm, so as to ensure that most or even all the light can pass through the composition or the polyimide. In addition, when the light emitted by the LED chip passes through the interface of two materials, the closer the refractive indexes of the two materials, the higher the light output efficiency. In order to be close to the refractive index of the material (such as die bonding glue) contacting with the filament substrate (or base layer), the organosilicon-modified polyimide composition has a refractive index of 1.4˜1.7, preferably 1.4˜1.55. In order to use the organosilicon-modified polyimide resin composition as substrate in the filament, the organosilicon-modified polyimide resin composition is required to have good light transmittance at the peak wavelength of InGaN of the blue-excited white LED. In order to obtain a good transmittance, the raw materials for synthesizing the organosilicon-modified polyimide, the thermal curing agent and the heat dispersing particles can be adjusted. Because the phosphor in the organosilicon-modified polyimide resin composition may have certain effect on the transmittance test, the organosilicon-modified polyimide resin composition used for the transmittance test does not comprise phosphor. Such an organosilicon-modified polyimide resin composition has a transmittance of 86˜93%, preferably 88˜91%, or preferably 89˜92%, or preferably 90˜93%. 
     In the reaction of anhydride and diamine to produce polyimide, the anhydride and the diamine may vary. In other words, the polyimides produced from different anhydrides and different diamines may have different light transmittances. The aliphatic organosilicon-modified polyimide resin composition comprises the aliphatic organosilicon-modified polyimide and the thermal curing agent, while the fluorinated aromatic organosilicon-modified polyimide resin composition comprises the fluorinated aromatic organosilicon-modified polyimide and the thermal curing agent. Since the aliphatic organosilicon-modified polyimide has an alicyclic structure, the aliphatic organosilicon-modified polyimide resin composition has a relatively high light transmittance. In addition, the fluorinated aromatic, semi-aliphatic and full aliphatic polyimides all have good light transmittance in respect of the blue LED chips. The fluorinated aromatic organosilicon-modified polyimide is synthesized from a siloxane-type diamine, an aromatic diamine comprising a fluoro (F) group (or referred to as fluorinated aromatic diamine) and an aromatic dianhydride comprising a fluoro (F) group (or referred to as fluorinated aromatic anhydride). In other words, both Ar 1  and Ar 2  comprise a fluoro (F) group. The semi-aliphatic and full aliphatic organosilicon-modified polyimides are synthesized from a dianhydride, a siloxane-type diamine and at least one diamine not comprising an aromatic structure (e.g. a benzene ring) (or referred to as aliphatic diamine), or from a diamine (one of the diamine is siloxane-type diamine) and at least one dianhydride not comprising an aromatic structure (e.g. a benzene ring) (or referred to as aliphatic anhydride). In other words, at least one of Ar 1  and Ar 2  has an alicyclic hydrocarbon structure. 
     Although blue LED chips have a main light-emitting wavelength of 450 nm, they may still emit a minor light having a shorter wavelength of around 400 nm, due to the difference in the conditions during the manufacture of the chips and the effect of the environment. The fluorinated aromatic, semi-aliphatic and full aliphatic polyimides have different absorptions to the light having a shorter wavelength of 400 nm. The fluorinated aromatic polyimide has an absorbance of about 20% to the light having a shorter wavelength of around 400 nm, i.e. the light transmittance of the light having a wavelength of 400 nm is about 80% after passing through the fluorinated aromatic polyimide. The semi-aliphatic and full aliphatic polyimides have even lower absorbance to the light having a shorter wavelength of 400 nm than the fluorinated aromatic polyimide, which is only 12%. Accordingly, in an embodiment, if the LED chips used in the LED filament have a uniform quality, and emit less blue light having a shorter wavelength, the fluorinated aromatic organosilicon-modified polyimide may be used to produce the filament substrate or the light-conversion layer. In another embodiment, if the LED chips used in the LED filament have different qualities, and emit more blue light having a shorter wavelength, the semi-aliphatic or full aliphatic organosilicon-modified polyimides may be used to produce the filament substrate or the light-conversion layer. 
     Adding different thermal curing agents imposes different effects on the light transmittance of the organosilicon-modified polyimide. Table 1-1 shows the effect of the addition of different thermal curing agents on the light transmittance of the full aliphatic organosilicon-modified polyimide. At the main light-emitting wavelength of 450 nm for the blue LED chip, the addition of different thermal curing agents renders no significant difference to the light transmittance of the full aliphatic organosilicon-modified polyimide; while at a short wavelength of 380 nm, the addition of different thermal curing agents does affect the light transmittance of the full aliphatic organosilicon-modified polyimide. The organosilicon-modified polyimide itself has a poorer transmittance to the light having a short wavelength (380 nm) than to the light having a long wavelength (450 nm). However, the extent of the difference varies with the addition of different thermal curing agents. For example, when the thermal curing agent KF105 is added to the full aliphatic organosilicon-modified polyimide, the extent of the reduction in the light transmittance is less. In comparison, when the thermal curing agent 2021p is added to the full aliphatic organosilicon-modified polyimide, the extent of the reduction in the light transmittance is more. Accordingly, in an embodiment, if the LED chips used in the LED filament have a uniform quality, and emit less blue light having a short wavelength, the thermal curing agent BPA or the thermal curing agent 2021p may be added. In comparison, in an embodiment, if the LED chips used in the LED filament have different qualities, and emit more blue light having a short wavelength, the thermal curing agent KF105 may be used. Both Table 1-1 and Table 1-2 show the results obtained in the transmittance test using Shimadzu UV-Vis Spectrometer UV-1800. The light transmittances at wavelengths 380 nm, 410 nm and 450 nm are tested based on the light emission of white LEDs. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1-1 
               
             
            
               
                   
                   
               
               
                   
                   
                   
                 Mechanical 
               
               
                   
                 Thermal Curing 
                 Light Transmittance (%) 
                 Strength 
               
            
           
           
               
               
               
               
               
               
            
               
                 Organosilicon- 
                 Agent 
                   
                 Film 
                   
                 Tensile 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Modified 
                   
                 Amount 
                   
                   
                   
                 Thickness 
                 Elongation 
                 Strength 
               
               
                 Polyimides 
                 Types 
                 (%) 
                 380 nm 
                 410 nm 
                 450 nm 
                 (μm) 
                 (%) 
                 (MPa) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Full Aliphatic 
                 BPA 
                 8.0 
                 87.1 
                 89.1 
                 90.6 
                 44 
                 24.4 
                 10.5 
               
               
                 Full Aliphatic 
                 X22-163 
                 8.0 
                 86.6 
                 88.6 
                 90.2 
                 44 
                 43.4 
                 8.0 
               
               
                 Full Aliphatic 
                 KF105 
                 8.0 
                 87.2 
                 88.9 
                 90.4 
                 44 
                 72.6 
                 7.1 
               
               
                 Full Aliphatic 
                 EHPE3150 
                 8.0 
                 87.1 
                 88.9 
                 90.5 
                 44 
                 40.9 
                 13.1 
               
               
                 Full Aliphatic 
                 2021p 
                 8.0 
                 86.1 
                 88.1 
                 90.1 
                 44 
                 61.3 
                 12.9 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1-2 
               
             
            
               
                   
                   
               
               
                   
                 Thermal 
                 Light Transmittance (%) 
                 Mechanical Strength 
               
            
           
           
               
               
               
               
               
               
            
               
                 Organosilicon- 
                 Curing Agent 
                   
                 Film 
                   
                 Tensile 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Modified 
                   
                 Amount 
                   
                   
                   
                 Thickness 
                 Elongation 
                 Strength 
               
               
                 Polyimide 
                 Type 
                 (%) 
                 380 nm 
                 410 nm 
                 450 nm 
                 (mm) 
                 (%) 
                 (MPa) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Full Aliphatic 
                 BPA 
                 4.0 
                 86.2 
                 88.4 
                 89.7 
                 44 
                 22.5 
                 9.8 
               
               
                 Full Aliphatic 
                   
                 8.0 
                 87.1 
                 89.1 
                 90.6 
                 44 
                 24.4 
                 10.5 
               
               
                 Full Aliphatic 
                   
                 12.0 
                 87.3 
                 88.9 
                 90.5 
                 44 
                 20.1 
                 9.0 
               
               
                   
               
            
           
         
       
     
     Even when the same thermal curing agent is added, different added amount thereof will have different effects on the light transmittance. Table 1-2 shows that when the added amount of the thermal curing agent BPA to the full aliphatic organosilicon-modified polyimide is increased from 4% to 8%, the light transmittance increases. However, when the added amount is further increased to 12%, the light transmittance keeps almost constant. It is shown that the light transmittance increases with the increase of the added amount of the thermal curing agent, but after the light transmittance increases to certain degree, adding more thermal curing agent will have limited effect on the light transmittance. 
     Different heat dispersing particles would have different transmittances. If heat dispersing particles with low light transmittance or low light reflection are used, the light transmittance of the organosilicon-modified polyimide resin composition will be lower. The heat dispersing particles in the organosilicon-modified polyimide resin composition of the present disclosure are preferably selected to be transparent powders or particles with high light transmittance or high light reflection. Since the soft filament for the LED is mainly for the light emission, the filament substrate should have good light transmittance. In addition, when two or more types of heat dispersing particles are mixed, particles with high light transmittance and those with low light transmittance can be used in combination, wherein the proportion of particles with high light transmittance is higher than that of particles with low light transmittance. In an embodiment, for example, the weight ratio of particles with high light transmittance to particles with low light transmittance is 3˜5:1. 
     Different siloxane content also affects the light transmittance. As can be seen from Table 2, when the siloxane content is only 37 wt %, the light transmittance is only 85%. When the siloxane content is increase to above 45%, the light transmittance exceeds 94%. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                   
                   
                   
                 Elongation 
                   
                   
                   
               
               
                 Organosilicon- 
                 Siloxane 
                 Thermal 
                   
                 Tensile 
                 Elastic 
                 at 
                   
                   
                 Resistance 
               
               
                 Modified 
                 Content 
                 Curing 
                 Tg 
                 Strength 
                 Modulus 
                 Break 
                   
                 Chemical 
                 to 
               
               
                 Polyimide 
                 (wt %) 
                 Agent 
                 (° C.) 
                 (MPa) 
                 (GPa) 
                 (%) 
                 Transmittance 
                 Resistance 
                 Thermochromism 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 37 
                 BPA 
                 158 
                 33.2 
                 1.7 
                 10 
                 85 
                 Δ 
                 83 
               
               
                 2 
                 41 
                 BPA 
                 142 
                 38.0 
                 1.4 
                 12 
                 92 
                 ∘ 
                 90 
               
               
                 3 
                 45 
                 BPA 
                 145 
                 24.2 
                 1.1 
                 15 
                 97 
                 Δ 
                 90 
               
               
                 4 
                 64 
                 BPA 
                 30 
                 8.9 
                 0.04 
                 232 
                 94 
                 ∘ 
                 92 
               
               
                 5 
                 73 
                 BPA 
                 0 
                 1.8 
                 0.001 
                 291 
                 96 
                 ∘ 
                 95 
               
               
                   
               
            
           
         
       
     
     Heat Resistance 
     The factors affecting the heat resistance of the organosilicon-modified polyimide resin composition include at least the type of the main material, the siloxane content, and the type and content of the modifier (thermal curing agent). 
     All the organosilicon-modified polyimide resin composition synthesized from fluorinated aromatic, semi-aliphatic and, full aliphatic organosilicon-modified polyimide have superior heat resistance, and are suitable for producing the filament substrate or the light-conversion layer. Detailed results from the accelerated heat resistance and aging tests (300° C.×1 hr) show that the fluorinated aromatic organosilicon-modified polyimide has better heat resistance than the aliphatic organosilicon-modified polyimide. Accordingly, in an embodiment, if a high power, high brightness LED chip is used as the LED filament, the fluorinated aromatic organosilicon-modified polyimide may be used to produce the filament substrate or the light-conversion layer. 
     The siloxane content in the organosilicon-modified polyimide will affect the resistance to thermochromism of the organosilicon-modified polyimide resin composition. The resistance to thermochromism refers to the transmittance determined at 460 nm after placing the sample at 200° C. for 24 hours. As can be seen from Table 2, when the siloxane content is only 37 wt %, the light transmittance after 24 hours at 200° C. is only 83%. As the siloxane content is increased, the light transmittance after 24 hours at 200° C. increases gradually. When the siloxane content is 73 wt %, the light transmittance after 24 hours at 200° C. is still as high as 95%. Accordingly, increasing the siloxane content can effectively increase the resistance to thermochromism of the organosilicon-modified polyimide. 
     Adding a thermal curing agent can lead to increased heat resistance and glass transition temperature. As shown in  FIG. 23 , A1 and A2 represent the curves before and after adding the thermal curing agent, respectively; and the curves D1 and D2 represent the values after differential computation on curves A1 and A2, respectively, representing the extent of the change of curves A1 and A2. As can be seen from the analysis results from TMA (thermomechanical analysis) shown in  FIG. 23 , the addition of the thermal curing agent leads to a trend that the thermal deformation slows down. Accordingly, adding a thermal curing agent can lead to increase of the heat resistance. 
     In the cross-linking reaction between the organosilicon-modified polyimide and the thermal curing agent, the thermal curing agent should have an organic group which is capable of reacting with the functional group having active hydrogen in the polyimide. The amount and the type of the thermal curing agent have certain effects on chromism, mechanical property and refractive index of the substrate. Accordingly, a thermal curing agent with good heat resistance and transmittance can be selected. Examples of the thermal curing agent include epoxy resin, isocyanate, bismaleimide, and bisoxazoline compounds. The epoxy resin may be bisphenol A epoxy resin, such as BPA; or siloxane-type epoxy resin, such as KF105, X22-163, and X22-163A; or alicylic epoxy resin, such as 3,4-epoxycyclohexylmethyl3,4-epoxycyclohexanecarboxylate (2021P), EHPE3150, and EHPE3150CE. Through the bridging reaction by the epoxy resin, a three dimensional bridge structure is formed between the organosilicon-modified polyimide and the epoxy resin, increasing the structural strength of the adhesive itself. In an embodiment, the amount of the thermal curing agent may be determined according to the molar amount of the thermal curing agent reacting with the functional group having active hydrogen in the organosilicon-modified polyimide. In an embodiment, the molar amount of the functional group having active hydrogen reacting with the thermal curing agent is equal to that of the thermal curing agent. For example, when the molar amount of the functional group having active hydrogen reacting with the thermal curing agent is 1 mol, the molar amount of the thermal curing agent is 1 mol. 
     Thermal Conductivity 
     The factors affecting the thermal conductivity of the organosilicon-modified polyimide resin composition include at least the type and content of the phosphor, the type and content of the heat dispersing particles and the addition and the type of the coupling agent. In addition, the particle size and the particle size distribution of the heat dispersing particles would also affect the thermal conductivity. 
     The organosilicon-modified polyimide resin composition may also comprise phosphor for obtaining the desired light-emitting properties. The phosphor can convert the wavelength of the light emitted from the light-emitting semiconductor. For example, yellow phosphor can convert blue light to yellow light, and red phosphor can convert blue light to red light. Examples of yellow phosphor include transparent phosphor such as (Ba,Sr,Ca) 2 SiO 4 :Eu, and (Sr,Ba) 2 SiO 4 :Eu(barium orthosilicate (BOS)); silicate-type phosphor having a silicate structure such as Y 3 Al 5 O 12 :Ce(YAG(yttrium.aluminum.garnet):Ce), and Tb 3 Al 3 O 12 :Ce(YAG(terbium.aluminum.garnet):Ce); and oxynitride phosphor such as Ca-α-SiAlON. Examples of red phosphor include nitride phosphor, such as CaAlSiN 3 :Eu, and CaSiN 2 :Eu. Examples of green phosphor include rare earth-halide phosphor, and silicate phosphor. The ratio of the phosphor in the organosilicon-modified polyimide resin composition may be determined arbitrarily according to the desired light-emitting property. In addition, since the phosphor have a thermal conductivity which is significantly higher than that of the organosilicon-modified polyimide resin, the thermal conductivity of the organosilicon-modified polyimide resin composition as a whole will increase as the ratio of the phosphor in the organosilicon-modified polyimide resin composition increases. Accordingly, in an embodiment, as long as the light-emitting property is fulfilled, the content of the phosphor can be suitably increased to increase the thermal conductivity of the organosilicon-modified polyimide resin composition, which is beneficial to the heat dissipation of the filament substrate or the light-conversion layer. Furthermore, when the organosilicon-modified polyimide resin composition is used as the filament substrate, the content, shape and particle size of the phosphor in the organosilicon-modified polyimide resin composition also have certain effect on the mechanical property (such as the elastic modulus, elongation, tensile strength) and the warpage extent of the substrate. In order to render superior mechanical property and thermal conductivity as well as small warpage extent to the substrate, the phosphor included in the organosilicon-modified polyimide resin composition are particulate, and the shape thereof may be sphere, plate or needle, preferably sphere. The maximum average length of the phosphor (the average particle size when they are spherical) is above 0.1 μm, preferably over 1 μm, further preferably 1˜100 μm, and more preferably 1˜50 μm. The content of phosphor is no less than 0.05 times, preferably no less than 0.1 times, and no more than 8 times, preferably no more than 7 times, the weight of the organosilicon-modified polyimide. For example, when the weight of the organosilicon-modified polyimide is 100 parts in weight, the content of the phosphor is no less than 5 parts in weight, preferably no less than 10 parts in weight, and no more than 800 parts in weight, preferably no more than 700 parts in weight. When the content of the phosphor in the organosilicon-modified polyimide resin composition exceeds 800 parts in weight, the mechanical property of the organosilicon-modified polyimide resin composition may not achieve the strength as required for a filament substrate, resulting in the increase of the defective rate of the product. In an embodiment, two kinds of phosphor are added at the same time. For example, when red phosphor and green phosphor are added at the same time, the added ratio of red phosphor to green phosphor is 1:5˜8, preferably 1:6˜7. In another embodiment, red phosphor and yellow phosphor are added at the same time, wherein the added ratio of red phosphor to yellow phosphor is 1:5˜8, preferably 1:6˜7. In another embodiment, three or more kinds of phosphor are added at the same time. 
     The main purposes of adding the heat dispersing particles are to increase the thermal conductivity of the organosilicon-modified polyimide resin composition, to maintain the color temperature of the light emission of the LED chip, and to prolong the service life of the LED chip. Examples of the heat dispersing particles include silica, alumina, magnesia, magnesium carbonate, aluminum nitride, boron nitride and diamond. Considering the dispersity, silica, alumina or combination thereof is preferably. The shape of the heat dispersing particles may be sphere, block, etc., where the sphere shape encompasses shapes which are similar to sphere. In an embodiment, heat dispersing particles may be in a shape of sphere or non-sphere, to ensure the dispersity of the heat dispersing particles and the thermal conductivity of the substrate, wherein the added weight ratio of the spherical and non-spherical heat dispersing particles is 1:0.15˜0.35. 
     Table 3-1 shows the relationship between the content of the heat dispersing particles and the thermal conductivity of the organosilicon-modified polyimide resin composition. As the content of the heat dispersing particles increases, the thermal conductivity of the organosilicon-modified polyimide resin composition increases. However, when the content of the heat dispersing particles in the organosilicon-modified polyimide resin composition exceeds 1200 parts in weight, the mechanical property of the organosilicon-modified polyimide resin composition may not achieve the strength as required for a filament substrate, resulting in the increase of the defective rate of the product. In an embodiment, high content of heat dispersing particles with high light transmittance or high reflectivity (such as SiO 2 , Al 2 O 3 ) may be added, which, in addition to maintaining the transmittance of the organosilicon-modified polyimide resin composition, increases the heat dissipation of the organosilicon-modified polyimide resin composition. The heat conductivities shown in Tables 3-1 and 3-2 were measured by a thermal conductivity meter DRL-III manufactured by Xiangtan city instruments Co., Ltd. under the following test conditions: heating temperature: 90° C.; cooling temperature: 20° C.; load: 350N, after cutting the resultant organosilicon-modified polyimide resin composition into test pieces having a film thickness of 300 μm and a diameter of 30 mm. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 3-1 
               
               
                   
               
             
            
               
                 Weight Ratio [wt %] 
                 0.0% 
                 37.9% 
                 59.8% 
                 69.8% 
                 77.6% 
                 83.9% 
                 89.0% 
               
               
                 Volume Ratio [vol %] 
                 0.0% 
                 15.0% 
                 30.0% 
                 40.0% 
                 50.0% 
                 60.0% 
                 70.0% 
               
               
                 Thermal Conductivity [W/m * K] 
                 0.17 
                 0.20 
                 0.38 
                 0.54 
                 0.61 
                 0.74 
                 0.81 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE 3-2 
               
             
            
               
                   
                   
               
               
                   
                 Specification 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Average Particle Size [μm] 
                 2.7  
                 6.6  
                 9.0  
                 9.6  
                 13    
                 4.1  
                 12    
               
               
                 Particle Size Distribution [μm] 
                 1~7 
                 1~20 
                 1~30 
                 0.2~30 
                 0.2~110 
                 0.1~20 
                 0.1~100 
               
               
                 Thermal Conductivity [W/m * K] 
                 1.65 
                 1.48 
                 1.52 
                 1.86 
                 1.68 
                 1.87 
                 2.10 
               
               
                   
               
            
           
         
       
     
     For the effects of the particle size and the particle size distribution of the heat dispersing particles on the thermal conductivity of the organosilicon-modified polyimide resin composition, see both Table 3-2 and  FIG. 24 . Table 3-2 and  FIG. 24  show seven heat dispersing particles with different specifications added into the organosilicon-modified polyimide resin composition in the same ratio and their effects on the thermal conductivity. The particle size of the heat dispersing particles suitable to be added to the organosilicon-modified polyimide resin composition can be roughly classified as small particle size (less than 1 μm), medium particle size (1-30 μm) and large particle size (above 30 μm). 
     Comparing specifications 1, 2 and 3, wherein only heat dispersing particles with medium particle size but different average particle sizes are added, when only heat dispersing particles with medium particle size are added, the average particle size of the heat dispersing particles does not significantly affect the thermal conductivity of the organosilicon-modified polyimide resin composition. Comparing specifications 3 and 4, wherein the average particle sizes are similar, the specification 4 comprising small particle size and medium particle size obviously exhibits higher thermal conductivity than specification 3 comprising only medium particle size. Comparing specifications 4 and 6, which comprise heat dispersing particles with both small particle size and medium particle size, although the average particle sizes of the heat dispersing particles are different, they have no significant effect on the thermal conductivity of the organosilicon-modified polyimide resin composition. Comparing specifications 4 and 7, specification 7, which comprises heat dispersing particles with large particle size in addition to small particle size and medium particle size, exhibits the most excellent thermal conductivity. Comparing specifications 5 and 7, which both comprise heat dispersing particles with large, medium and small particle sizes and have similar average particle sizes, the thermal conductivity of specification 7 is significant superior to that of specification 5 due to the difference in the particle size distribution. See  FIG. 24  for the particle size distribution of specification 7, the curve is smooth, and the difference in the slope is small, showing that specification 7 not only comprises each particle size, but also have moderate proportions of each particle size, and the particle size is normally distributed. For example, the small particle size represents about 10%, the medium particle size represents about 60%, and the large particle size represents about 30%. In contrast, the curve for specification 5 has two regions with large slopes, which locate in the region of particle size 1-2 μm and particle size 30-70 μm, respectively, indicating that most of the particle size in specification 5 is distributed in particle size 1-2 μm and particle size 30-70 μm, and only small amount of heat dispersing particles with particle size 3-20 μm are present, i.e. exhibiting a two-sided distribution. 
     Accordingly, the extent of the particle size distribution of the heat dispersing particles affecting the thermal conductivity is greater than that of the average particle size of the heat dispersing particles. When large, medium and small particle sizes of the heat dispersing particles are added, and the small particle size represents about 5-20%, the medium particle size represents about 50-70%, and large particle size represents about 20-40%, the organosilicon-modified polyimide resin will have optimum thermal conductivity. That is because when large, medium and small particle sizes are present, there would be denser packing and contacting each other of heat dispersing particles in a same volume, so as to form an effective heat dissipating route. 
     In an embodiment, for example, alumina with a particle size distribution of 0.1˜100 μm and an average particle size of 12 μm or with a particle size distribution of 0.1˜20 μm and an average particle size of 4.1 μm is used, wherein the particle size distribution is the range of the particle size of alumina. In another embodiment, considering the smoothness of the substrate, the average particle size may be selected as ⅕˜⅖, preferably ⅕˜⅓ of the thickness of the substrate. The amount of the heat dispersing particles may be 1˜12 times the weight (amount) of the organosilicon-modified polyimide. For example, if the amount of the organosilicon-modified polyimide is 100 parts in weight, the amount of the heat dispersing particles may be 100˜1200 parts in weight, preferably 400˜900 parts in weight. Two different heat dispersing particles such as silica and alumina may be added at the same time, wherein the weight ratio of alumina to silica may be 0.4˜25:1, preferably 1˜10:1. 
     In the synthesis of the organosilicon-modified polyimide resin composition, a coupling agent such as a silicone coupling agent may be added to improve the adhesion between the solid material (such as the phosphor and/or the heat dispersing particles) and the adhesive material (such as the organosilicon-modified polyimide), and to improve the dispersion uniformity of the whole solid materials, and to further improve the heat dissipation and the mechanical strength of the light-conversion layer. The coupling agent may also be titanate coupling agent, preferably epoxy titanate coupling agent. The amount of the coupling agent is related to the amount of the heat dispersing particles and the specific surface area thereof. The amount of the coupling agent=(the amount of the heat dispersing particles*the specific surface area of the heat dispersing particles)/the minimum coating area of the coupling agent. For example, when an epoxy titanate coupling agent is used, the amount of the coupling agent=(the amount of the heat dispersing particles*the specific surface area of the heat dispersing particles)/331.5. 
     In other specific embodiments of the present invention, in order to further improve the properties of the organosilicon-modified polyimide resin composition in the synthesis process, an additive such as a defoaming agent, a leveling agent or an adhesive may be selectively added in the process of synthesizing the organosilicon-modified polyimide resin composition, as long as it does not affect light resistance, mechanical strength, heat resistance and chromism of the product. The defoaming agent is used to eliminate the foams produced in printing, coating and curing. For example, acrylic acid or silicone surfactants may be used as the defoaming agent. The leveling agent is used to eliminate the bumps in the film surface produced in printing and coating. Specifically, adding preferably 0.01˜2 wt % of a surfactant component can inhibit foams. The coating film can be smoothened by using acrylic acid or silicone leveling agents, preferably non-ionic surfactants free of ionic impurities. Examples of the adhesive include imidazole compounds, thiazole compounds, triazole compounds, organoaluminum compounds, organotitanium compounds and silane coupling agents. Preferably, the amount of these additives is no more than 10% of the weight of the organosilicon-modified polyimide. When the mixed amount of the additive exceeds 10 wt %, the physical properties of the resultant coating film tend to decline, and it even leads to deterioration of the light resistance due to the presence of the volatile components. 
     Mechanical Strength 
     The factors affecting the mechanical strength of the organosilicon-modified polyimide resin composition include at least the type of the main material, the siloxane content, the type of the modifier (thermal curing agent), the phosphor and the content of the heat dispersing particles. 
     Different organosilicon-modified polyimide resins have different properties. Table 4 lists the main properties of the fluorinated aromatic, semi-aliphatic and full aliphatic organosilicon-modified polyimide, respectively, with a siloxane content of about 45% (wt %). The fluorinated aromatic has the best resistance to thermo chromism. The full aliphatic has the best light transmittance. The fluorinated aromatic has both high tensile strength and high elastic modulus. The conditions for testing the mechanical strengths shown in Table 4˜6: the organosilicon-modified polyimide resin composition has a thickness of 50 μm and a width of 10 mm, and the tensile strength of the film is determined according to ISO527-3:1995 standard with a drawing speed of 10 mm/min. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                   
                   
                   
                   
                 Elongation 
                   
                   
               
               
                 Organosilicon- 
                 Siloxane 
                 Thermal 
                 Tensile 
                 Elastic 
                 at 
                   
                 Resistance 
               
               
                 Modified 
                 Content 
                 Curing 
                 Strength 
                 Modulus 
                 Break 
                   
                 to 
               
               
                 Polyimide 
                 (wt %) 
                 Agent 
                 (MPa) 
                 (GPa) 
                 (%) 
                 Transmittance 
                 Thermochromism 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Fluorinated 
                 44 
                 X22-163 
                 22.4 
                 1.0 
                 83 
                 96 
                 95 
               
               
                 Aromatic 
               
               
                 Semi-Aliphatic 
                 44 
                 X22-163 
                 20.4 
                 0.9 
                 30 
                 96 
                 91 
               
               
                 Full Aliphatic 
                 47 
                 X22-163 
                 19.8 
                 0.8 
                 14 
                 98 
                 88 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                   
                 Addition 
                   
                   
                   
                   
                 Elongation 
                   
                   
                   
               
               
                 Siloxane 
                 of 
                 Thermal 
                   
                 Tensile 
                 Elastic 
                 at 
                   
                   
                 Resistance 
               
               
                 Content 
                 Phosphor, 
                 Curing 
                 Tg 
                 Strength 
                 Modulus 
                 Break 
                   
                 Chemical 
                 to 
               
               
                 (wt %) 
                 Alumina 
                 Agent 
                 (° C.) 
                 (MPa) 
                 (GPa) 
                 (%) 
                 Transmittance 
                 Resistance 
                 Thermochromism 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 37 
                 x 
                 BPA 
                 158 
                 33.2 
                 1.7 
                 10 
                 85 
                 Δ 
                 83 
               
               
                 37 
                 ∘ 
                 BPA 
                 — 
                 26.3 
                 5.1 
                 0.7 
                 — 
                 — 
                 — 
               
               
                 41 
                 x 
                 BPA 
                 142 
                 38.0 
                 1.4 
                 12 
                 92 
                 ∘ 
                 90 
               
               
                 41 
                 ∘ 
                 BPA 
                 — 
                 19.8 
                 4.8 
                 0.8 
                 — 
                 — 
                 — 
               
               
                 45 
                 x 
                 BPA 
                 145 
                 24.2 
                 1.1 
                 15 
                 97 
                 Δ 
                 90 
               
               
                 45 
                 ∘ 
                 BPA 
                 — 
                 21.5 
                 4.2 
                 0.9 
                 — 
                 — 
                 — 
               
               
                 64 
                 x 
                 BPA 
                  30 
                 8.9 
                 0.04 
                 232 
                 94 
                 ∘ 
                 92 
               
               
                 64 
                 ∘ 
                 BPA 
                 — 
                 12.3 
                 3.1 
                 1.6 
                 — 
                 — 
                 — 
               
               
                 73 
                 x 
                 BPA 
                  0 
                 1.8 
                 0.001 
                 291 
                 96 
                 ∘ 
                 95 
               
               
                 73 
                 ∘ 
                 BPA 
                 — 
                 9.6 
                 2.5 
                 2 
                 — 
                 — 
                 — 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 6 
               
             
            
               
                   
                   
               
               
                   
                 Thermal Curing 
                 Transmittance (%) 
                 Mechanical Strength 
               
            
           
           
               
               
               
               
               
               
            
               
                 Organosilicon- 
                 Agent 
                   
                 Film 
                   
                 Tensile 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Modified 
                   
                 Amount 
                   
                   
                   
                 Thickness 
                 Elongation 
                 Strength 
               
               
                 Polyimide 
                 Type 
                 (%) 
                 380 nm 
                 410 nm 
                 450 nm 
                 (μm) 
                 (%) 
                 (MPa) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Full Aliphatic 
                 BPA 
                 8.0 
                 87.1 
                 89.1 
                 90.6 
                 44 
                 24.4 
                 10.5 
               
               
                 Full Aliphatic 
                 X22-163 
                 8.0 
                 86.6 
                 88.6 
                 90.2 
                 40 
                 43.4 
                 8.0 
               
               
                 Full Aliphatic 
                 KF105 
                 12.0 
                 87.5 
                 89.2 
                 90.8 
                 43 
                 80.8 
                 7.5 
               
               
                 Full Aliphatic 
                 EHPE3150 
                 7.5 
                 87.1 
                 88.9 
                 90.5 
                 44 
                 40.9 
                 13.1 
               
               
                 Full Aliphatic 
                 2021p 
                 5.5 
                 86.1 
                 88.1 
                 90.1 
                 44 
                 64.0 
                 12.5 
               
               
                   
               
            
           
         
       
     
     In the manufacture of the filament, the LED chip and the electrodes are first fixed on the filament substrate formed by the organosilicon-modified polyimide resin composition with a die bonding glue, followed by a wiring procedure, in which electric connections are established between adjacent LED chips and between the LED chip and the electrode with wires. To ensure the quality of die bonding and wiring, and to improve the product quality, the filament substrate should have a certain level of elastic modulus to resist the pressing force in the die bonding and wiring processes. Accordingly, the filament substrate should have an elastic modulus more than 2.0 GPa, preferably 2˜6 GPa, more preferably 4˜6 GPa. Table 5 shows the effects of different siloxane contents and the presence of particles (phosphor and alumina) on the elastic modulus of the organosilicon-modified polyimide resin composition. Where no fluorescent powder or alumina particle is added, the elastic modulus of the organosilicon-modified polyimide resin composition is always less than 2.0 GPa, and as the siloxane content increases, the elastic modulus tends to decline, i.e. the organosilicon-modified polyimide resin composition tends to soften. However, where phosphor and alumina particles are added, the elastic modulus of the organosilicon-modified polyimide resin composition may be significantly increased, and is always higher than 2.0 GPa. Accordingly, the increase in the siloxane content may lead to softening of the organosilicon-modified polyimide resin composition, which is advantageous for adding more fillers, such as more phosphor or heat dispersing particles. In order for the substrate to have superior elastic modulus and thermal conductivity, appropriate particle size distribution and mixing ratio may be selected so that the average particle size is within the range from 0.1 μm to 100 μm or from 1 μm to 50 μm. 
     In order for the LED filament to have good bending properties, the filament substrate should have an elongation at break of more than 0.5%, preferably 1˜5%, most preferably 1.5˜5%. As shown in Table 5, where no fluorescent powder or alumina particle is added, the organosilicon-modified polyimide resin composition has excellent elongation at break, and as the siloxane content increases, the elongation at break increases and the elastic modulus decreases, thereby reducing the occurrence of warpage. In contrast, where phosphor and alumina particles are added, the organosilicon-modified polyimide resin composition exhibits decreased elongation at break and increased elastic modulus, thereby increasing the occurrence of warpage. 
     By adding a thermal curing agent, not only the heat resistance and the glass transition temperature of the organosilicon-modified polyimide resin are increased, the mechanical properties, such as tensile strength, elastic modulus and elongation at break, of the organosilicon-modified polyimide are also increased. Adding different thermal curing agents may lead to different levels of improvement. Table 6 shows the tensile strength and the elongation at break of the organosilicon-modified polyimide resin composition after the addition of different thermal curing agents. For the full aliphatic organosilicon-modified polyimide, the addition of the thermal curing agent EHPE3150 leads to good tensile strength, while the addition of the thermal curing agent KF105 leads to good elongation. 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Specific Information of BPA 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                 Content of 
                 Equivalent 
                   
               
               
                 Product 
                 Viscosity at 
                 Color 
                 Hydrolysable 
                 of Epoxy 
                 Hue 
               
               
                 Name 
                 25° C.(mPa · s) 
                 (G) 
                 Chlorine (mg/kg) 
                 (g/mol) 
                 APHA 
               
               
                   
               
               
                 BPA 
                 11000~15000 
                 ≤1 
                 ≤300 
                 184~194 
                 ≤30 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 Specific Information of 2021P 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Specific 
                 Melting 
                 Boiling 
                 Water 
                   
                   
               
               
                 Product 
                 Viscosity 
                 Gravity 
                 Point 
                 Point 
                 Content 
                 Equivalent of 
                 Hue 
               
               
                 Name 
                 at25° C. (mPa · s) 
                 (25/25° C.) 
                 (° C.) 
                 (° C./4 hPa) 
                 (%) 
                 Epoxy (g/mol) 
                 APHA 
               
               
                   
               
               
                 2021P 
                 250 
                 1.17 
                 −20 
                 188 
                 0.01 
                 130 
                 10 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 Specific Information of EHPE3150 and EHPE3150CE 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Viscosity at 
                   
                 Softening 
                 Equivalent of 
                 Hue 
               
               
                 Product Name 
                 25° C. (mPa · s) 
                 Appearance 
                 Point 
                 Epoxy(g/mol) 
                 APHA 
               
               
                   
               
               
                 EHPE3150 
                 — 
                 Transparent 
                 75 
                 177 
                 20 (in 25% 
               
               
                   
                   
                 Plate Solid 
                   
                   
                 acetone 
               
               
                   
                   
                   
                   
                   
                 solution) 
               
               
                 EHPE3150CE 
                 50,000 
                 Light Yellow 
                 — 
                 151 
                 60 
               
               
                   
                   
                 Transparent 
               
               
                   
                   
                 Liquid 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 10 
               
             
            
               
                   
               
               
                 Specific Information of PAME, KF8010, X22-161A, 
               
               
                 X22-161B, NH15D, X22-163, X22-163A and KF-105 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Specific 
                 Refractive 
                   
               
               
                 Product 
                 Viscosity at 
                 Gravity 
                 Index 
                 Equivalent of 
               
               
                 Name 
                 25° C.(mm2/s) 
                 at 25° C. 
                 at 25° C. 
                 Functional Group 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 PAME 
                 4 
                 0.90 
                 1.448 
                 130 
                 g/mol 
               
               
                 KF8010 
                 12 
                 1.00 
                 1.418 
                 430 
                 g/mol 
               
               
                 X22-161A 
                 25 
                 0.97 
                 1.411 
                 800 
                 g/mol 
               
               
                 X22-161B 
                 55 
                 0.97 
                 1.408 
                 1500 
                 g/mol 
               
               
                 NH15D 
                 13 
                 0.95 
                 1.403 
                 1.6-2.1 
                 g/mmol 
               
               
                 X22-163 
                 15 
                 1.00 
                 1.450 
                 200 
                 g/mol 
               
               
                 X22-163A 
                 30 
                 0.98 
                 1.413 
                 1000 
                 g/mol 
               
               
                 KF-105 
                 15 
                 0.99 
                 1.422 
                 490 
                 g/mol 
               
               
                   
               
            
           
         
       
     
     The organosilicon-modified polyimide resin composition of the present embodiment may be used in a form of film or as a substrate together with a support to which it adheres. The film forming process comprises three steps: (a) coating step: spreading the above organosilicon-modified polyimide resin composition on a peelable body by coating to form a film; (b) heating and drying step: heating and drying the film together with the peelable body to remove the solvent from the film; and (c) peeling step: peeling the film from the peelable body after the drying is completed to give the organosilicon-modified polyimide resin composition in a form of film. The above peelable body may be a centrifugal film or other materials which do not undergo chemical reaction with the organosilicon-modified polyimide resin composition, e.g., PET centrifugal film. 
     The organosilicon-modified polyimide resin composition may be adhered to a support to give an assembly film, which may be used as the substrate. The process of forming the assembly film comprises two steps: (a) coating step: spreading the above organosilicon-modified polyimide resin composition on a support by coating to from an assembly film; and (b) heating and drying step: heating and drying the assembly film to remove the solvent from the film. 
     In the coating step, roll-to-roll coating devices such as roller coater, mold coating machine and blade coating machine, or simple coating means such as printing, inkjeting, dispensing and spraying may be used. 
     The drying method in the above heating and drying step may be drying in vacuum, drying by heating, or the like. The heating may be achieved by a heat source such as an electric heater or a heating media to produce heat energy and indirect convection, or by infrared heat radiation emitted from a heat source. 
     A film (composite film) with high thermal conductivity can be obtained from the above organosilicon-modified polyimide resin composition by coating and then drying and curing, so as to achieve any one or combination of the following properties: superior light transmittance, chemical resistance, heat resistance, thermal conductivity, film mechanical property and light resistance. The temperature and time in the drying and curing step may be suitably selected according to the solvent and the coated film thickness of the organosilicon-modified polyimide resin composition. The weight change of the organosilicon-modified polyimide resin composition before and after the drying and curing as well as the change in the peaks in the IR spectrum representing the functional groups in the thermal curing agent can be used to determine whether the drying and curing are completed. For example, when an epoxy resin is used as the thermal curing agent, whether the difference in the weight of the organosilicon-modified polyimide resin composition before and after the drying and curing is equal to the weight of the added solvent as well as the increase or decrease of the epoxy peak before and after the drying and curing are used to determine whether the drying and curing are completed. 
     In an embodiment, the amidation is carried out in a nitrogen atmosphere, or vacuum defoaming is employed in the synthesis of the organosilicon-modified polyimide resin composition, or both, so that the volume percentage of the cells in the organosilicon-modified polyimide resin composition composite film is 5˜20%, preferably 5˜10%. As shown in  FIG. 25B , the organosilicon-modified polyimide resin composition composite film is used as the substrate for the LED soft filament. The substrate  420   b  has an upper surface  420   b   1  and an opposite lower surface  420   b   2 .  FIG. 25A  shows the surface morphology of the substrate after gold is scattered on the surface thereof as observed with vega3 electron microscope from Tescan Corporation. As can be seen from  FIG. 25B  and the SEM image of the substrate surface shown in  FIG. 25A , there is a cell  4   d  in the substrate, wherein the cell  4   d  represents 5˜20% by volume, preferably 5˜10% by volume, of the substrate  420   b , and the cross section of the cell  4   d  is irregular.  FIG. 25B  shows the cross-sectional scheme of the substrate  420   b , wherein the dotted line is the baseline. The upper surface  420   b   1  of the substrate comprises a first area  4   a  and a second area  4   b , wherein the second area  4   b  comprises a cell  4   d , and the first area  4   a  has a surface roughness which is less than that of the second area  4   b . The light emitted by the LED chip passes through the cell in the second area and is scattered, so that the light emission is more uniform. The lower surface  420   b   2  of the substrate comprises a third area  4   c , which has a surface roughness which is higher than that of the first area  4   a . When the LED chip is positioned in the first area  4   a , the smoothness of the first area  4   a  is favorable for subsequent bonding and wiring. When the LED chip is positioned in the second area  4   b  or the third area  4   c , the area of contact between the die bonding glue and substrate is large, which improves the bonding strength between the die bonding glue and substrate. Therefore, by positioning the LED chip on the upper surface  420   b   1 , bonding and wiring as well as the bonding strength between the die bonding glue and substrate can be ensured at the same time. When the organosilicon-modified polyimide resin composition is used as the substrate of the LED soft filament, the light emitted by the LED chip is scattered by the cell in the substrate, so that the light emission is more uniform, and glare can be further improved at the same time. In an embodiment, the surface of the substrate  420   b  may be treated with a silicone resin or a titanate coupling agent, preferably a silicone resin comprising methanol or a titanate coupling agent comprising methanol, or a silicone resin comprising isopropanol. The cross section of the treated substrate is shown in  FIG. 25C . The upper surface  420   b   1  of the substrate has relatively uniform surface roughness. The lower surface  420   b   2  of the substrate comprises a third area  4   c  and a fourth area  4   e , wherein the third area  4   c  has a surface roughness which is higher than that of the fourth area  4   e . The surface roughness of the upper surface  420   b   1  of the substrate may be equal to that of the fourth area  4   e . The surface of the substrate  420   b  may be treated so that a material with a high reactivity and a high strength can partially enter the cell  4   d , so as to improve the strength of the substrate. 
     When the organosilicon-modified polyimide resin composition is prepared by vacuum defoaming, the vacuum used in the vacuum defoaming may be −0.5˜-0.09 MPa, preferably −0.2˜-0.09 MPa. When the total weight of the raw materials used in the preparation of the organosilicon-modified polyimide resin composition is less than or equal to 250 g, the revolution speed is 1200˜2000 rpm, the rotation speed is 1200˜2000 rpm, and time for vacuum defoaming is 3˜8 min. This not only maintains certain amount of cells in the film to improve the uniformity of light emission, but also keeps good mechanical properties. The vacuum may be suitably adjusted according to the total weight of the raw materials used in the preparation of the organosilicon-modified polyimide resin composition. Normally, when the total weight is higher, the vacuum may be reduced, while the stirring time and the stirring speed may be suitably increased. 
     According to the present disclosure, a resin having superior transmittance, chemical resistance, resistance to thermochromism, thermal conductivity, film mechanical property and light resistance as required for a LED soft filament substrate can be obtained. In addition, a resin film having a high thermal conductivity can be formed by simple coating methods such as printing, inkjeting, and dispensing. 
     When the organosilicon-modified polyimide resin composition composite film is used as the filament substrate (or base layer), the LED chip is a hexahedral luminous body. In the production of the LED filament, at least two sides of the LED chip are coated by a top layer. When the prior art LED filament is lit up, non-uniform color temperatures in the top layer and the base layer would occur, or the base layer would give a granular sense. Accordingly, as a filament substrate, the composite film is required to have superior transparency. In other embodiments, sulfonyl group, non-coplanar structure, meta-substituted diamine, or the like may be introduced into the backbone of the organosilicon-modified polyimide to improve the transparency of the organosilicon-modified polyimide resin composition. In addition, in order for the bulb employing said filament to achieve omnidirectional illumination, the composite film as the substrate should have certain flexibility. Therefore, flexible structures such as ether (such as (4,4′-bis(4-amino-2-trifluoromethylphenoxy)diphenyl ether), carbonyl, methylene may be introduced into the backbone of the organosilicon-modified polyimide. In other embodiments, a diamine or dianhydride comprising a pyridine ring may be employed, in which the rigid structure of the pyridine ring can improve the mechanical properties of the composite film. Meanwhile, by using it together with a strong polar group such as —F, the composite film may have superior light transmittance. Examples of the anhydride comprising a pyridine ring include 2,6-bis(3′,4′-dicarboxyphenyl)-4-(3″,5″-bistrifluoromethylphenyl)pyridine dianhydride. 
     The LED filament structure in the aforementioned embodiments is mainly applicable to the LED light bulb product, so that the LED light bulb can achieve the omni-directional light illuminating effect through the flexible bending characteristics of the single LED filament. The specific embodiment in which the aforementioned LED filament applied to the LED light bulb is further explained below. 
     Please refer to  FIG. 26A .  FIG. 26A  illustrates a perspective view of an LED light bulb according to the third embodiment of the present disclosure. According to the third embodiment, the LED light bulb  20   c  comprises a lamp housing  12 , a bulb base  16  connected with the lamp housing  12 , two conductive supports  51   a ,  51   b  disposed in the lamp housing  12 , a driving circuit  518  electrically connected with both the conductive supports  51   a ,  51   b  and the bulb base  16 , a stem  19 , supporting arms  15  and a single LED filament  100 . 
     The lamp housing  12  is a material which is preferably light transmissive or thermally conductive, such as, glass or plastic, but not limited thereto. In implementation, the lamp housing  12  may be doped with a golden yellow material or its surface coated with a yellow film to absorb a portion of the blue light emitted by the LED chip to reduce the color temperature of the light emitted by the LED light bulb  20   c . In other embodiments of the present invention, the lamp housing  12  includes a layer of luminescent material (not shown), which may be formed on the inner surface or the outer surface of the lamp housing  12  according to design requirements or process feasibility, or even integrated in the material of the lamp housing  12 . The luminescent material layer comprises low reabsorption semiconductor nanocrystals (hereinafter referred to as quantum dots), the quantum dots comprises a core, a protective shell and a light absorbing shell, and the light absorbing shell is disposed between the core and the protective shell. The core emits the emissive light with emission wavelength, and the light absorbing shell emits the excited light with excitation wavelength. The emission wavelength is longer than the excitation wavelength, and the protective shell provides the stability of the light. 
     The core is a semiconductor nanocrystalline material, typically the combination of at least of one metal and at least one non-metal. The core is prepared by combining a coation precursor(s) with an anion precursor(s). The metal for the core is most preferably selected from Zn, Cd, Hg, Ga, In, Ti, Pb or a rare earth. The non-metal is most preferably selected from O, S, Se, P, As or Te. The cationic precursor ion may include all transition metals and rare earth elements, and the anionic precursor ions may be chosen from O, S, Se, Te, N, P, As, F, CL, and Br. Furthermore, cationic precursors may include elements or compounds, such as elements, covalent compounds, or ionic compounds, including but are not limited to, oxides, hydroxides, coordination compounds, or metal salts, which serves as a source for the electropositive element or elements in the resulting nanocrystal core or shell materials. 
     The cationic precursor solution may include a metal oxide, a metal halide, a metal nitride, a metal ammonia complex, a metal amine, a metal amide, a metal imide, a metal carboxylate, a metal acetylacetonate, a metal dithiolate, a metal carbonyl, a metal cyanide, a metal isocyanide, a metal nitrile, a metal peroxide, a metal hydroxide, a metal hydride, a metal ether complex, a metal diether complex, a metal triether compound, a metal carbonate, a metal nitrate, a metal nitrite, a metal sulfate, a metal alkoxide, a metal siloxide, a metal thiolate, a metal dithiolate, a metal disulfide, a metal carbamate, a metal dialky carbamate, a metal pyridine complex, a metal dipyridine complex, a metal phenanthroline complex, a metal terpyridine complex, a metal diamine complex, a metal triamine complex, a metal diimine, a metal pyridine diimine, a metal pyrazollborate, a metal bis(pyrazole)borate, a metal tris(pyrazole)borate, a metal nitrosyl, a metal thiocarbamate, metal diazabutadiene, a metal dithiocarbamate, a metal dialkylacetamide, a metal dialkylformamide, a metal formamidinate, a metal phosphine complex, a metal arsine complex, a metal diphosphine complex, a metal diarsine complex, a metal oxalate, a metal imidazole, a metal pyrazolate, a metal Schiff base complex, a metal porphyrin, a metal phthalocyanine, a metal subphthalocyanine, a metal picolinate, a metal piperidine complex, a metal pyrazolyl, a metal salicylaldehyde, a metal ethylenediamine, a metal triflate compound or any combination thereof. Preferably, the cationic precursor solution may include a metal oxide, a metal carbonate, a metal bicarbonate, a metal sulfate, a metal sulfite, a metal phosphate, a metal phosphite, a metal halide, a metal carboxylate, a metal hydroxide, a metal alkoxide, a metal thiolate, a metal amide, a metal imide, a metal alkyl, a metal aryl, a metal coordination complex, a metal solvate, a metal salt or a combination thereof. Most preferably, the cationic precursor is a metal oxide or metal salt precursor and may be selected from zinc stearate, zinc myristate, zinc acetate, and manganese stearate. 
     Anionic precursors may also include elements, covalent compounds, or ionic compounds, which are used as one or more electronegative elements in the resulting nanocrystals. These definitions expect to be able to prepare ternary compounds, quaternary compounds and even more complex species using the methods disclosed in the present invention, in which case more than one cationic precursor and/or more than one anion precursor can be used. When two or more cationic elements are used during a given monolayer growth, if the other part of the nanocrystalline contains only a single cationic, the resulting nanocrystals have a cationic alloy at the specified single layer. The same method can be used to prepare nanocrystals with anionic alloys. 
     The above method is applicable to the core/shell nanocrystals prepared using a series of cationic precursor compounds of core and shell materials, for example, precursors of Group II metals (eg, Zn, Cd or Hg), precursors of Group III metals (eg, Al, Ga or In), a precursor of a Group IV metal (for example, Ge, Sn or Pb), or a transition metal (for example, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc), Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, etc.). 
     The components of the light absorbing shell may be the same or different from the composition of the core. Typically, the light absorbing shell material has the same lattice structure as the material selected for the core. For example, if CdSe is used as the emission region material, the absorption region material may be CdS. The light absorbing shell material is chosen to provide good absorption characteristics and can depend on the light source. For example, CdS can be a good choice for the absorption region when the excitation comes from a typical blue LED (within the wavelength range between 440 and 470 nm) solid state illumination. For example, if the excitation originates from a purple LED to produce a red LED by frequency down-conversion, then ZnSe or ZnSe x S 1-x  (where x is greater than or equal to 0 and less than or equal to 1) is a preferred choice for the absorption region. As another example, if one wishes to obtain near-infrared emission from a quantum dot for bio-medical applications (700-1000 nm) by using a red light source, then CdSe and InP often work as the absorption region material. 
     The protected area (wide bandgap semiconductor or insulator) at the outermost outer shell of the quantum dot provides the desired chemical and optical stability to the quantum dots. In general, a protective shell (also known as a protected area) neither effectively absorbs light nor emits directional photons within the preferred excitation window described above. This is because it has a wide band gap. For example, ZnS and GaN are examples of protective shell materials. Metal oxides can also be utilized. In certain embodiments, an organic polymer can be used as a protective shell. The thickness of the protective shell is typically in the range between 1 and 20 monolayers. Moreover, the thickness can also be increased as needed, but this also increases production costs. 
     A light absorbing shell includes a plurality of mono layers that form a compositional gradient. For example, the light absorbing shell can include three components varying in a ratio of 1:0:1 in a mono layer located closest to the core to a ratio 0:1:1 in a mono layer located closest to the protective shell. By way of example, three useful components are Cd, Zn, and S and for instance, a mono layer closest to the core may have a component CdS (ratio 1:0:1), a mono layer closest to the protective shell may have a component corresponding to ZnS (Ratio 0:1:1), and the intermediate mono layer between the core and the protective shell may have a component corresponding to ZnSe x S 1-x  having a ratio (X):(1−X):1, and wherein X greater than or equal to 0 and less than or equal to 1. In this case, X is larger for a mono layer closer to the core than a mono layer that closer to the protective shell. In another embodiment, the transition shell consists of three components, the ratio from the single layer closest to the core to the single layer closest to the protective shell: 0.9:0.1:1, 0.8:0.2:1, 0.6:0.4:1, 0.4:0.6:1, and 0.2:0.8:1. Other combinations of Cd, Zn, S, and Se alloys can also be used as transition shells instead of ZnSe x S 1-x  as long as they have suitable lattice matching parameters. In one embodiment, a suitable transition shell includes one shell having Cd, Zn, and S components and the following layers listed from the layer closest to the light absorbing shell to the layer closest to the protective shell: Cd 0.9 Zn 0.1 S, Cd 0.8 Zn 0.2 S, Cd 0.6 Zn 0.4 S, Cd 0.4 Zn 0.6 S, Cd 0.2 Zn 0.8 S. 
     The LED filament  100  shown in  FIG. 26A  is bent to form a contour resembling to a circle while being observed from the top view of  FIG. 26A . According to the embodiment of  FIG. 26A , the LED filament  100  is bent to form a wave shape from side view. The shape of the LED filament  100  is novel and makes the illumination more uniform. In comparison with a LED bulb having multiple LED filaments, single LED filament  100  has less connecting spots. In implementation, single LED filament  100  has only two connecting spots such that the probability of defect soldering or defect mechanical pressing is decreased. 
     The stem  19  has a stand  19   a  extending to the center of the bulb shell  12 . The stand  19   a  supports the supporting arms  15 . The first end of each of the supporting arms  15  is connected with the stand  19   a  while the second end of each of the supporting arms  15  is connected with the LED filament  100 . 
     Please refer to  FIG. 26B  which illustrates an enlarged cross-sectional view of the dashed-line circle of  FIG. 26A . The second end of each of the supporting arms  15  has a clamping portion  15   a  which clamps the body of the LED filament  100 . The clamping portion  15   a  may, but not limited to, clamp at either the wave crest or the wave trough. Alternatively, the clamping portion  15   a  may clamp at the portion between the wave crest and the wave trough. The shape of the clamping portion  15   a  may be tightly fitted with the outer shape of the cross-section of the LED filament  100 . The dimension of the inner shape (through hole) of the clamping portion  15   a  may be a little bit smaller than the outer shape of the cross-section of the LED filament  100 . During manufacturing process, the LED filament  100  may be passed through the inner shape of the clamping portion  15   a  to form a tight fit. Alternatively, the clamping portion  15   a  may be formed by a bending process. Specifically, the LED filament  100  may be placed on the second end of the supporting arm  15  and a clamping tooling is used to bend the second end into the clamping portion to clamp the LED filament  100 . 
     The supporting arms  15  may be, but not limited to, made of carbon steel spring to provide with adequate rigidity and flexibility so that the shock to the LED light bulb caused by external vibrations is absorbed and the LED filament  100  is not easily to be deformed. Since the stand  19   a  extending to the center of the bulb shell  12  and the supporting arms  15  are connected to a portion of the stand  19   a  near the top thereof, the position of the LED filaments  100  is at the level close to the center of the bulb shell  12 . Accordingly, the illumination characteristics of the LED light bulb  20   c  are close to that of the traditional light bulb including illumination brightness. The illumination uniformity of LED light bulb  20   c  is better. In the embodiment, at least a half of the LED filaments  100  is around a center axle of the LED light bulb  20   c . The center axle is coaxial with the axle of the stand  19   a.    
     In the embodiment, the first end of the supporting arm  15  is connected with the stand  19   a  of the stem  19 . The clamping portion of the second end of the supporting arm  15  is connected with the outer insulation surface of the LED filaments  100  such that the supporting arms  15  are not used as connections for electrical power transmission. In an embodiment where the stem  19  is made of glass, the stem  19  would not be cracked or exploded because of the thermal expansion of the supporting arms  15  of the LED light bulb  20   c . Additionally, there may be no stand in an LED light bulb. The supporting arm  15  may be fixed to the stem or the bulb shell directly to eliminate the negative effect to illumination caused by the stand. 
     The supporting arm  15  is thus non-conductive to avoid a risk that the glass stem  19  may crack due to the thermal expansion and contraction of the metal filament in the supporting arm  15  under the circumstances that the supporting arm  15  is conductive and generates heat when current passes through the supporting arm  15 . 
     In different embodiments, the second end of the supporting arm  15  may be directly inserted inside the LED filament  100  and become an auxiliary piece in the LED filament  100 , which can enhance the mechanical strength of the LED filament  100 . Relative embodiments are described later. 
     The inner shape (the hole shape) of the clamping portion  15   a  fits the outer shape of the cross section of the LED filament  100 ; therefore, based upon a proper design, the cross section of the LED filament  100  may be oriented to face towards a predetermined orientation. For example, as shown in  FIG. 26B , the LED filament  100  comprises a top layer  420   a , LED chips  104 , and a base layer  420   b . The LED chips  104  are aligned in line along the axial direction (or an elongated direction) of the LED filament  100  and are disposed between the top layer  420   a  and the base layer  420   b . The top layer  420   a  of the LED filament  100  is oriented to face towards ten o&#39;clock in  FIG. 26B . A lighting face of the whole LED filament  100  may be oriented to face towards the same orientation substantially to ensure that the lighting face of the LED filament  100  is visually identical. The LED filament  100  comprises a main lighting face Lm and a subordinate lighting face Ls corresponding to the LED chips. If the LED chips in the LED filament  100  are wire bonded and are aligned in line, a face of the top layer  420   a  away from the base layer  420   b  is the main lighting face Lm, and a face of the base layer  420   b  away from the top layer  420   a  is the subordinate lighting face Ls. The main lighting face Lm and the subordinate lighting face Ls are opposite to each other. When the LED filament  100  emits light, the main lighting face Lm is the face through which the largest amount of light rays passes, and the subordinate lighting face Ls is the face through which the second largest amount of light rays passes. In the embodiment, there is, but is not limited to, a conductive foil  530  formed between the top layer  420   a  and the base layer  420   b , which is utilized for electrical connection between the LED chips. In the embodiment, the LED filament  100  wriggles with twists and turns while the main lighting face Lm is always towards outside. That is to say, any portion of the main lighting face Lm is towards the bulb shell  12  or the bulb base  16  and is away from the stem  19  at any angle, and the subordinate lighting face Ls is always towards the stem  19  or towards the top of the stem  19  (the subordinate lighting face Ls is always towards inside). 
     The LED filament  100  shown in  FIG. 26A  is curved to form a circular shape in a top view while the LED filament is curved to form a wave shape in a side view. The wave shaped structure is not only novel in appearance but also guarantees that the LED filament  100  illuminates evenly. In the meantime, the single LED filament  100 , comparing to multiple LED filaments, requires less joint points (e.g., pressing points, fusing points, or welding points) for being connected to the conductive supports  51   a ,  51   b . In practice, the single LED filament  100  (as shown in  FIG. 26A ) requires only two joint points respectively formed on the two conductive electrodes, which effectively lowers the risk of fault welding and simplifies the process of connection comparing to the mechanically connection in the tightly pressing manner. 
     Please refer to  FIG. 26C .  FIG. 26C  is a projection of a top view of an LED filament of the LED light bulb  20   c  of  FIG. 26A . As shown in  FIG. 26C , in an embodiment, the LED filament may be curved to form a wave shape resembling to a circle observed in a top view to surround the center of the light bulb or the stem. In different embodiments, the LED filament observed in the top view can form a quasi-circle or a quasi U shape. 
     As shown in  FIG. 26B  and  FIG. 26C , the LED filament  100  surrounds with the wave shape resembling to a circle and has a quasi-symmetric structure in the top view, and the lighting face of the LED filament  100  is also symmetric, e.g., the main lighting face Lm in the top view may faces outwardly; therefore, the LED filament  100  may generate an effect of an omnidirectional light due to a symmetry characteristic with respect to the quasi-symmetric structure of the LED filament  100  and the arrangement of the lighting face of the LED filament  100  in the top view. Whereby, the LED light bulb  20   c  as a whole may generate an effect of an omnidirectional light close to a 360 degrees illumination. Additionally, the two joint points may be close to each other such that the conductive supports  51   a ,  51   b  are substantially below the LED filament  100 . Visually, the conductive supports  51   a ,  51   b  keeps a low profile and is integrated with the LED filament  100  to show an elegance curvature. 
     Please refer to  FIG. 27A  and  FIG. 27B .  FIG. 27A  is a perspective view of an LED light bulb according to an embodiment of the present invention.  FIG. 27B  is a front view (or a side view) of an LED light bulb of  FIG. 27A . The LED light bulb  20   d  shown in  FIG. 27A  and  FIG. 27B  is analogous to the LED light bulb  20   c  shown in  FIG. 26A . As shown in  FIG. 27A  and  FIG. 27B , the LED light bulb  20   d  comprises a bulb shell  12 , a bulb base  16  connected to the bulb shell  12 , two conductive supports  51   a ,  51   b  disposed in the bulb shell  12 , supporting arms  15 , a stem  19 , and one single LED filament  100 . The stem  19  comprises a stem bottom and a stem top opposite to each other. The stem bottom is connected to the bulb base  16 . The stem top extends to inside of the bulb shell  12  (e.g., extending to the center of the bulb shell  12 ) along an elongated direction of the stem  19 . For example, the stem top may be substantially located at a center of the inside of the bulb shell  12 . In the embodiment, the stem  19  comprises the stand  19   a . Herein the stand  19   a  is deemed as a part of the whole stem  19  and thus the top of the stem  19  is the same as the top of the stand  19   a . The two conductive supports  51   a ,  51   b  are connected to the stem  19 . The LED filament  100  comprises a filament body and two conductive electrodes  506 . The two conductive electrodes  506  are at two opposite ends of the filament body. The filament body is the part of the LED filament  100  without the conductive electrodes  506 . The two conductive electrodes  506  are respectively connected to the two conductive supports  51   a ,  51   b . The filament body is around the stem  19 . An end of the supporting arm  15  is connected to the stem  19  and another end of the supporting arm  15  is connected to the filament body. 
     Please refer to  FIG. 27C .  FIG. 27C  is a top view of the LED light bulb  20   d  of  FIG. 27A . As shown in  FIG. 27B  and  FIG. 27C , the filament body comprises a main lighting face Lm and a subordinate lighting face Ls. Any portion of the main lighting face Lm is towards the bulb shell  12  or the bulb base  16  at any angle, and any portion of the subordinate lighting face Ls is towards the stem  19  or towards the top of the stem  19 , i.e., the subordinate lighting face Ls is towards inside of the LED light bulb  20   d  or towards the center of the bulb shell  12 . In other words, when a user observes the LED light bulb  20   d  from outside, the user would see the main lighting face Lm of the LED filament  100   d  at any angle. Based upon the configuration, the effect of illumination is better. 
     According to different embodiments, the LED filament  100  in different LED light bulbs (e.g., the LED light bulb  20   a ,  20   b ,  20   c , or  20   d ) may be formed with different shapes or curves while all of the LED filaments  100  are configured to have symmetry characteristic. The symmetry characteristic is beneficial of creating an even, wide distribution of light rays, so that the LED light bulb is capable of generating an omnidirectional light effect. The symmetry characteristic of the LED filament  100  is discussed below. 
     The definition of the symmetry characteristic of the LED filament  100  may be based on four quadrants defined in a top view of an LED light bulb. The four quadrants may be defined in a top view of an LED light bulb (e.g., the LED light bulb  20   b  shown in  FIG. 1B  or the LED light bulb  20   c  shown in  FIG. 26A ), and the origin of the four quadrants may be defined as a center of a stem/stand of the LED light bulb in the top view (e.g., a center of the top of the stand of the stem  19  shown in  FIG. 1B  or a center of the top of the stand  19   a  shown in  FIG. 26A ). The LED filament of the LED light bulb (e.g., the LED filaments  100  shown in  FIG. 1B  and  FIG. 26A ) in the top view may be presented as an annular structure, shape or, contour. The LED filament presented in the four quadrants in the top view may be symmetric. 
     For example, the brightness presented by a portion of the LED filament in the first quadrant in the top view is symmetric with that presented by a portion of the LED filament in the second quadrant, in the third quadrant, or in the fourth quadrant in the top view while the LED filament operates. In some embodiments, the structure of a portion of the LED filament in the first quadrant in the top view is symmetric with that of a portion of the LED filament in the second quadrant, in the third quadrant, or in the fourth quadrant in the top view. In addition, an emitting direction of a portion of the LED filament in the first quadrant in the top view is symmetric with that of a portion of the LED filament in the second quadrant, in the third quadrant, or in the fourth quadrant in the top view. 
     In another embodiment, an arrangement of LED chips in a portion of the LED filament in the first quadrant (e.g., a density variation of the LED chips in the portion of the LED filament in the first quadrant) in the top view is symmetric with an arrangement of LED chips in a portion of the LED filament in the second quadrant, in the third quadrant, or in the fourth quadrant in the top view. 
     In another embodiment, a power configuration of LED chips with different power in a portion of the LED filament in the first quadrant in the top view is symmetric with a power configuration of LED chips with different power in a portion of the LED filament in the second quadrant, in the third quadrant, or in the fourth quadrant in the top view. 
     In another embodiment, refractive indexes of segments of a portion of the LED filament in the first quadrant in the top view are symmetric with refractive indexes of segments of a portion of the LED filament in the second quadrant, in the third quadrant, or in the fourth quadrant in the top view while the segments may be defined by distinct refractive indexes. 
     In another embodiment, surface roughness of segments of a portion of the LED filament in the first quadrant in the top view are symmetric with surface roughness of segments of a portion of the LED filament in the second quadrant, in the third quadrant, or in the fourth quadrant in the top view while the segments may be defined by distinct surface roughness. 
     The LED filament presented in the four quadrants in the top view may be in point symmetry (e.g., being symmetric with the origin of the four quadrants) or in line symmetry (e.g., being symmetric with one of the two axis the four quadrants). 
     A tolerance (a permissible error) of the symmetric structure of the LED filament in the four quadrants in the top view may be up to 20%-50%. For example, in a case that the structure of a portion of the LED filament in the first quadrant is symmetric with that of a portion of the LED filament in the second quadrant, a designated point on portion of the LED filament in the first quadrant is defined as a first position, a symmetric point to the designated point on portion of the LED filament in the second quadrant is defined as a second position, and the first position and the second position may be exactly symmetric or be symmetric with 20%-50% difference. 
     In addition, a length of a portion of the LED filament in one of the four quadrants in the top view is substantially equal to that of a portion of the LED filament in another one of the four quadrants in the top view. The lengths of portions of the LED filament in different quadrants in the top view may also have 20%-50% difference. 
     The definition of the symmetry characteristic of the LED filament  100  may be based on four quadrants defined in a side view, in a front view, or in a rear view of an LED light bulb. In the embodiments, the side view may include a front view or a rear view of the LED light bulb. The four quadrants may be defined in a side view of an LED light bulb (e.g., the LED light bulb  20   a  shown in  FIG. 1A  or the LED light bulb  20   c  shown in  FIG. 26A ). In such case, an elongated direction of a stand (or a stem) from the bulb base  16  towards a top of the bulb shell  12  away from the bulb base  16  may be defined as the Y-axis, and the X-axis may cross a middle of the stand (e.g., the stand  19   a  of the LED light bulb  20   c  shown in  FIG. 26A ) while the origin of the four quadrants may be defined as the middle of the stand. In different embodiment, the X-axis may cross the stand at any point, e.g., the X-axis may cross the stand at the top of the stand, at the bottom of the stand, or at a point with a certain height (e.g., ⅔ height) of the stand. 
     In addition, portions of the LED filament presented in the first quadrant and the second quadrant (the upper quadrants) in the side view may be symmetric (e.g., in line symmetry with the Y-axis) in brightness, and portions of the LED filament presented in the third quadrant and the fourth quadrant (the lower quadrants) in the side view may be symmetric (e.g., in line symmetry with the Y-axis) in brightness; however, the brightness of the portions of the LED filament presented in the upper quadrants in the side view may be asymmetric with that of the portions of the LED filament presented in the lower quadrants in the side view. 
     In some embodiments, portions of the LED filament presented in the first quadrant and the second quadrant (the upper quadrants) in the side view may be symmetric (e.g., in line symmetry with the Y-axis) in structure; portions of the LED filament presented in the third quadrant and the fourth quadrant (the lower quadrants) in the side view may be symmetric (e.g., in line symmetry with the Y-axis) in structure. In addition, an emitting direction of a portion of the LED filament in the first quadrant in the side view is symmetric with that of a portion of the LED filament in the second quadrant in the side view, and an emitting direction of a portion of the LED filament in the third quadrant in the side view is symmetric with that of a portion of the LED filament in the fourth quadrant in the side view. 
     In another embodiment, an arrangement of LED chips in a portion of the LED filament in the first quadrant in the side view is symmetric with an arrangement of LED chips in a portion of the LED filament in the second quadrant in the side view, and an arrangement of LED chips in a portion of the LED filament in the third quadrant in the side view is symmetric with an arrangement of LED chips in a portion of the LED filament in the fourth quadrant in the side view. 
     In another embodiment, a power configuration of LED chips with different power in a portion of the LED filament in the first quadrant in the side view is symmetric with a power configuration of LED chips with different power in a portion of the LED filament in the second quadrant in the side view, and a power configuration of LED chips with different power in a portion of the LED filament in the third quadrant in the side view is symmetric with a power configuration of LED chips with different power in a portion of the LED filament in the fourth quadrant in the side view. 
     In another embodiment, refractive indexes of segments of a portion of the LED filament in the first quadrant in the side view are symmetric with refractive indexes of segments of a portion of the LED filament in the second quadrant in the side view, and refractive indexes of segments of a portion of the LED filament in the third quadrant in the side view are symmetric with refractive indexes of segments of a portion of the LED filament in the fourth quadrant in the side view while the segments may be defined by distinct refractive indexes. 
     In another embodiment, surface roughness of segments of a portion of the LED filament in the first quadrant in the side view are symmetric with surface roughness of segments of a portion of the LED filament in the second quadrant in the side view, and surface roughness of segments of a portion of the LED filament in the third quadrant in the side view are symmetric with surface roughness of segments of a portion of the LED filament in the fourth quadrant in the side view while the segments may be defined by distinct surface roughness. 
     Additionally, the portions of the LED filament presented in the upper quadrants in the side view may be asymmetric with the portions of the LED filament presented in the lower quadrants in the side view in brightness. In some embodiments, the portion of the LED filament presented in the first quadrant and the fourth quadrant in the side view is asymmetric in structure, in length, in emitting direction, in arrangement of LED chips, in power configuration of LED chips with different power, in refractive index, or in surface roughness, and the portion of the LED filament presented in the second quadrant and the third quadrant in the side view is asymmetric in structure, in length, in emitting direction, in arrangement of LED chips, in power configuration of LED chips with different power, in refractive index, or in surface roughness. In order to fulfill the illumination purpose and the requirement of omnidirectional lamps, light rays emitted from the upper quadrants (the portion away from the bulb base  16 ) in the side view should be greater than those emitted from the lower quadrants (the portion close to the bulb base  16 ). Therefore, the asymmetric characteristic of the LED filament of the LED light bulb between the upper quadrants and the lower quadrants in the side view may contribute to the omnidirectional requirement by concentrating the light rays in the upper quadrants. 
     A tolerance (a permissible error) of the symmetric structure of the LED filament in the first quadrant and the second quadrant in the side view may be 20%-50%. For example, a designated point on portion of the LED filament in the first quadrant is defined as a first position, a symmetric point to the designated point on portion of the LED filament in the second quadrant is defined as a second position, and the first position and the second position may be exactly symmetric or be symmetric with 20%-50% difference. 
     In addition, a length of a portion of the LED filament in the first quadrant in the side view is substantially equal to that of a portion of the LED filament in the second quadrant in the side view. A length of a portion of the LED filament in the third quadrant in the side view is substantially equal to that of a portion of the LED filament in the fourth quadrant in the side view. However, the length of the portion of the LED filament in the first quadrant or the second quadrant in the side view is different from the length of the portion of the LED filament in the third quadrant or the fourth quadrant in the side view. In some embodiment, the length of the portion of the LED filament in the third quadrant or the fourth quadrant in the side view may be less than that of the portion of the LED filament in the first quadrant or the second quadrant in the side view. The lengths of portions of the LED filament in the first and the second quadrants or in the third and the fourth quadrants in the side view may also have 20%-50% difference. 
     Please refer to  FIG. 27D .  FIG. 27D  is the LED filament  100  shown in  FIG. 27B  presented in two dimensional coordinate system defining four quadrants. The LED filament  100  in  FIG. 27D  is the same as that in  FIG. 27B , which is a front view (or a side view) of the LED light bulb  20   d  shown in  FIG. 27A . As shown in  FIG. 27B  and  FIG. 27D , the Y-axis is aligned with the stand  19   a  of the stem (i.e., being along the elongated direction of the stand  19   a ), and the X-axis crosses the stand  19   a  (i.e., being perpendicular to the elongated direction of the stand  19   a ). As shown in  FIG. 27D , the LED filament  100  in the side view can be divided into a first portion  100   p   1 , a second portion  100   p   2 , a third portion  100   p   3 , and a fourth portion  100   p   4  by the X-axis and the Y-axis. The first portion  100   p   1  of the LED filament  100  is the portion presented in the first quadrant in the side view. The second portion  100   p   2  of the LED filament  100  is the portion presented in the second quadrant in the side view. The third portion  100   p   3  of the LED filament  100  is the portion presented in the third quadrant in the side view. The fourth portion  100   p   4  of the LED filament  100  is the portion presented in the fourth quadrant in the side view. 
     As shown in  FIG. 27D , the LED filament  100  is in line symmetry. The LED filament  100  is symmetric with the Y-axis in the side view. That is to say, the geometric shape of the first portion  100   p   1  and the fourth portion  100   p   4  are symmetric with that of the second portion  100   p   2  and the third portion  100   p   3 . Specifically, the first portion  100   p   1  is symmetric to the second portion  100   p   2  in the side view. Particularly, the first portion  100   p   1  and the second portion  100   p   2  are symmetric in structure in the side view with respect to the Y-axis. In addition, the third portion  100   p   3  is symmetric to the fourth portion  100   p   4  in the side view. Particularly, the third portion  100   p   3  and the fourth portion  100   p   4  are symmetric in structure in the side view with respect to the Y-axis. 
     In the embodiment, as shown in  FIG. 27D , the first portion  100   p   1  and the second portion  100   p   2  presented in the upper quadrants (i.e., the first quadrant and the second quadrant) in the side view are asymmetric with the third portion  100   p   3  and the fourth portion  100   p   4  presented in the lower quadrants (i.e., the third quadrant and the fourth quadrant) in the side view. In particular, the first portion  100   p   1  and the fourth portion  100   p   4  in the side view are asymmetric, and the second portion  100   p   2  and the third portion  100   p   3  in the side view are asymmetric. According to an asymmetry characteristic of the structure of the filament  100  in the upper quadrants and the lower quadrants in  FIG. 27D , light rays emitted from the upper quadrants to pass through the upper bulb shell  12  (the portion away from the bulb base  16 ) would be greater than those emitted from the lower quadrants to pass through the lower bulb shell  12  (the portion close to the bulb base  16 ) in order to fulfill the illumination purpose and the requirement of omnidirectional lamps. 
     Based upon symmetry characteristic of LED filament  100 , the structures of the two symmetric portions of the LED filament  100  in the side view (the first portion  100   p   1  and the second portion  100   p   2  or the third portion  100   p   3  and the fourth portion  100   p   4 ) may be exactly symmetric or be symmetric with a tolerance in structure. The tolerance (or a permissible error) between the structures of the two symmetric portions of the LED filament  100  in the side view may be 20%-50% or less. 
     The tolerance can be defined as a difference in coordinates, i.e., x-coordinate or y-coordinate. For example, if there is a designated point on the first portion  100   p   1  of the LED filament  100  in the first quadrant and a symmetric point on the second portion  100   p   2  of the LED filament  100  in the second quadrant symmetric to the designated point with respect to the Y-axis, the absolute value of y-coordinate or the x-coordinate of the designated point may be equal to the absolute value of y-coordinate or the x-coordinate of the symmetric point or may have 20% difference comparing to the absolute value of y-coordinate or the x-coordinate of the symmetric point. 
     For example, as shown in  FIG. 27D , a designated point (x1, y1) on the first portion  100   p   1  of the LED filament  100  in the first quadrant is defined as a first position, and a symmetric point (x2, y2) on the second portion  100   p   2  of the LED filament  100  in the second quadrant is defined as a second position. The second position of the symmetric point (x2, y2) is symmetric to the first position of the designated point (x1, y1) with respect to the Y-axis. The first position and the second position may be exactly symmetric or be symmetric with 20%-50% difference. In the embodiment, the first portion  100   p   1  and the second portion  100   p   2  are exactly symmetric in structure. In other words, x2 of the symmetric point (x2, y2) is equal to negative x1 of the designated point (x1, y1), and y2 of the symmetric point (x2, y2) is equal to y1 of the designated point (x1, y1). 
     For example, as shown in  FIG. 27D , a designated point (x3, y3) on the third portion  100   p   3  of the LED filament  100  in the third quadrant is defined as a third position, and a symmetric point (x4, y4) on the fourth portion  100   p   4  of the LED filament  100  in the fourth quadrant is defined as a fourth position. The fourth position of the symmetric point (x4, y4) is symmetric to the third position of the designated point (x3, y3) with respect to the Y-axis. The third position and the fourth position may be exactly symmetric or be symmetric with 20%-50% difference. In the embodiment, the third portion  100   p   3  and the fourth portion  100   p   4  are symmetric with a tolerance (e.g., a difference in coordinates being less than 20%) in structure. In other words, the absolute value of x4 of the symmetric point (x4, y4) is unequal to the absolute value of x3 of the designated point (x3, y3), and the absolute value of y4 of the symmetric point (x4, y4) is unequal to the absolute value of y3 of the designated point (x3, y3). As shown in  FIG. 27D , the level of the designated point (x3, y3) is slightly lower than that of the symmetric point (x4, y4), and the designated point (x3, y3) is slightly closer to the Y-axis than the symmetric point (x4, y4) is. Accordingly, the absolute value of y4 is slightly less than that of y3, and the absolute value of x4 is slightly greater than that of x3. 
     As shown in  FIG. 27D , a length of the first portion  100   p   1  of the LED filament  100  in the first quadrant in the side view is substantially equal to a length of the second portion  100   p   2  of the LED filament  100  in the second quadrant in the side view. In the embodiment, the length is defined along an elongated direction of the LED filament  100  in a plane view (e.g., a side view, a front view, or a top view). For example, the first portion  100   p   1  elongates in the first quadrant in the side view shown in  FIG. 27D  to form a reversed “V” shape with two ends respectively contacting the X-axis and the Y-axis, and the length of the first portion  100   p   1  is defined along the reversed “V” shape between the X-axis and the Y-axis. 
     In addition, a length of the third portion  100   p   3  of the LED filament  100  in the third quadrant in the side view is substantially equal to a length of fourth portion  100   p   4  of the LED filament  100  in the fourth quadrant in the side view. Since the third portion  100   p   3  and the fourth portion  100   p   4  are symmetric with respect to the Y-axis with a tolerance in structure, there may be a slightly difference between the length of the third portion  100   p   3  and the length of fourth portion  100   p   4 . The difference may be 20%-50% or less. 
     As shown in  FIG. 27D , an emitting direction of a designated point of the first portion  100   p   1  and an emitting direction of a symmetric point of the second portion  100   p   2  symmetric to the designated point are symmetric in direction in the side view with respect to the Y-axis. In the embodiment, the emitting direction may be defined as a direction towards which the LED chips face. Since the LED chips face the main lighting face Lm, the emitting direction may also be defined as the normal direction of the main lighting face Lm. For example, the designated point (x1, y1) of the first portion  100   p   1  has an emitting direction ED which is upwardly in  FIG. 27D , and the symmetric point (x2, y2) of the second portion  100   p   2  has an emitting direction ED which is upwardly in  FIG. 27D . The emitting direction ED of the designated point (x1, y1) and the emitting direction ED of the symmetric point (x2, y2) are symmetric with respect to the Y-axis. In addition, the designated point (x3, y3) of the third portion  100   p   3  has an emitting direction ED towards a lower-left direction in  FIG. 27D , and the symmetric point (x4, y4) of the fourth portion  100   p   4  has an emitting direction ED towards a lower-right direction in  FIG. 27D . The emitting direction ED of the designated point (x3, y3) and the emitting direction ED of the symmetric point (x4, y4) are symmetric with respect to the Y-axis. 
     Please refer to  FIG. 27E .  FIG. 27E  is the LED filament  100  shown in  FIG. 27C  presented in two dimensional coordinate system defining four quadrants. The LED filament  100  in  FIG. 27E  is the same as that in  FIG. 27C , which is a top view of the LED light bulb  20   d  shown in  FIG. 27A . As shown in  FIG. 27C  and  FIG. 27E , the origin of the four quadrants is defined as a center of a stand  19   a  of the LED light bulb  20   d  in the top view (e.g., a center of the top of the stand  19   a  shown in  FIG. 27A ). In the embodiment, the Y-axis is vertical, and the X-axis is horizontal in  FIG. 27E . As shown in  FIG. 27E , the LED filament  100  in the top view can be divided into a first portion  100   p   1 , a second portion  100   p   2 , a third portion  100   p   3 , and a fourth portion  100   p   4  by the X-axis and the Y-axis. The first portion  100   p   1  of the LED filament  100  is the portion presented in the first quadrant in the top view. The second portion  100   p   2  of the LED filament  100  is the portion presented in the second quadrant in the top view. The third portion  100   p   3  of the LED filament  100  is the portion presented in the third quadrant in the top view. The fourth portion  100   p   4  of the LED filament  100  is the portion presented in the fourth quadrant in the top view. 
     In some embodiments, the LED filament  100  in the top view may be symmetric in point symmetry (being symmetric with the origin of the four quadrants) or in line symmetry (being symmetric with one of the two axis the four quadrants). In the embodiment, as shown in  FIG. 27E , the LED filament  100  in the top view is in line symmetry. In particular, the LED filament  100  in the top view is symmetric with the Y-axis. That is to say, the geometric shape of the first portion  100   p   1  and the fourth portion  100   p   4  are symmetric with that of the second portion  100   p   2  and the third portion  100   p   3 . Specifically, the first portion  100   p   1  is symmetric to the second portion  100   p   2  in the top view. Particularly, the first portion  100   p   1  and the second portion  100   p   2  are symmetric in structure in the top view with respect to the Y-axis. In addition, the third portion  100   p   3  is symmetric to the fourth portion  100   p   4  in the top view. Particularly, the third portion  100   p   3  and the fourth portion  100   p   4  are symmetric in structure in the top view with respect to the Y-axis. 
     Based upon symmetry characteristic of LED filament  100 , the structures of the two symmetric portions of the LED filament  100  in the top view (the first portion  100   p   1  and the second portion  100   p   2  or the third portion  100   p   3  and the fourth portion  100   p   4 ) may be exactly symmetric or be symmetric with a tolerance in structure. The tolerance (or a permissible error) between the structures of the two symmetric portions of the LED filament  100  in the top view may be 20%-50% or less. 
     For example, as shown in  FIG. 27E , a designated point (x1, y1) on the first portion  100   p   1  of the LED filament  100  in the first quadrant is defined as a first position, and a symmetric point (x2, y2) on the second portion  100   p   2  of the LED filament  100  in the second quadrant is defined as a second position. The second position of the symmetric point (x2, y2) is symmetric to the first position of the designated point (x1, y1) with respect to the Y-axis. The first position and the second position may be exactly symmetric or be symmetric with 20%-50% difference. In the embodiment, the first portion  100   p   1  and the second portion  100   p   2  are exactly symmetric in structure. In other words, x2 of the symmetric point (x2, y2) is equal to negative x1 of the designated point (x1, y1), and y2 of the symmetric point (x2, y2) is equal to y1 of the designated point (x1, y1). 
     For example, as shown in  FIG. 27E , a designated point (x3, y3) on the third portion  100   p   3  of the LED filament  100  in the third quadrant is defined as a third position, and a symmetric point (x4, y4) on the fourth portion  100   p   4  of the LED filament  100  in the fourth quadrant is defined as a fourth position. The fourth position of the symmetric point (x4, y4) is symmetric to the third position of the designated point (x3, y3) with respect to the Y-axis. The third position and the fourth position may be exactly symmetric or be symmetric with 20%-50% difference. In the embodiment, the third portion  100   p   3  and the fourth portion  100   p   4  are symmetric with a tolerance (e.g., a difference in coordinates being less than 20%) in structure. In other words, x4 of the symmetric point (x4, y4) is unequal to negative x3 of the designated point (x3, y3), and y4 of the symmetric point (x4, y4) is unequal to y3 of the designated point (x3, y3). As shown in  FIG. 27E , the level of the designated point (x3, y3) is slightly lower than that of the symmetric point (x4, y4), and the designated point (x3, y3) is slightly closer to the Y-axis than the symmetric point (x4, y4) is. Accordingly, the absolute value of y4 is slightly less than that of y3, and the absolute value of x4 is slightly greater than that of x3. 
     As shown in  FIG. 27E , a length of the first portion  100   p   1  of the LED filament  100  in the first quadrant in the top view is substantially equal to a length of the second portion  100   p   2  of the LED filament  100  in the second quadrant in the top view. In the embodiment, the length is defined along an elongated direction of the LED filament  100  in a plane view (e.g., a top view, a front view, or a top view). For example, the second portion  100   p   2  elongates in the second quadrant in the top view shown in  FIG. 27E  to form a reversed “L” shape with two ends respectively contacting the X-axis and the Y-axis, and the length of the second portion  100   p   2  is defined along the reversed “L” shape. 
     In addition, a length of the third portion  100   p   3  of the LED filament  100  in the third quadrant in the top view is substantially equal to a length of fourth portion  100   p   4  of the LED filament  100  in the fourth quadrant in the top view. Since the third portion  100   p   3  and the fourth portion  100   p   4  are symmetric with respect to the Y-axis with a tolerance in structure, there may be a slightly difference between the length of the third portion  100   p   3  and the length of fourth portion  100   p   4 . The difference may be 20%-50% or less. 
     As shown in  FIG. 27E , an emitting direction of a designated point of the first portion  100   p   1  and an emitting direction of a symmetric point of the second portion  100   p   2  symmetric to the designated point are symmetric in direction in the top view with respect to the Y-axis. In the embodiment, the emitting direction may be defined as a direction towards which the LED chips face. Since the LED chips face the main lighting face Lm, the emitting direction may also be defined as the normal direction of the main lighting face Lm. For example, the designated point (x1, y1) of the first portion  100   p   1  has an emitting direction ED towards right in  FIG. 27E , and the symmetric point (x2, y2) of the second portion  100   p   2  has an emitting direction ED towards left in  FIG. 27E . The emitting direction ED of the designated point (x1, y1) and the emitting direction ED of the symmetric point (x2, y2) are symmetric with respect to the Y-axis. In addition, the designated point (x3, y3) of the third portion  100   p   3  has an emitting direction ED towards a lower-left direction in  FIG. 27E , and the symmetric point (x4, y4) of the fourth portion  100   p   4  has an emitting direction ED towards a lower-right direction in  FIG. 27E . The emitting direction ED of the designated point (x3, y3) and the emitting direction ED of the symmetric point (x4, y4) are symmetric with respect to the Y-axis. In addition, an emitting direction ED of any designated point of the first portion  100   p   1  and an emitting direction ED of a corresponding symmetric point of the second portion  100   p   2  symmetric to the designated point are symmetric in direction in the top view with respect to the Y-axis. An emitting direction ED of any designated point of the third portion  100   p   3  and an emitting direction ED of a corresponding symmetric point of the fourth portion  100   p   4  symmetric to the designated point are symmetric in direction in the top view with respect to the Y-axis. 
     Definition of the omni-directional light depends on regions and varies over time. Depending on different institutions and countries, LED light bulbs which claim omni-directional light may need to meet different standards. For example, page 24 of the ENERGY STAR Program Requirements for Lamps (bulbs)—Eligibility Criteria Version 1.0 defines that an omnidirectional lamp in base-on position has to emit at least 5% of total flux (lm) in 135° to 180° zone, that 90% of measured intensity values may vary by no more than 25% from the average of all measured values in all planes, and that luminous intensity (cd) is measured within each vertical plane at a 5° vertical angle increment (maximum) from 0° to 135°. Japanese JEL 801 requires luminous flux of an LED lamp within a 120 degrees zone about a light axis shall not be less than 70% of total flux. Because the above embodiment possesses a symmetrical arrangement of LED filament, an LED light bulb with the LED filament is able to meet various standards of omni-directional lamps. 
     Referring to  FIGS. 28A, 28B, 28C  and  FIG. 28D ,  FIG. 28A  illustrates a schematic diagram of an LED light bulb  40   a  according to an embodiment of the present invention,  FIG. 28B  to  FIG. 28D  are a side view, another side view and the top view of the LED light bulb, respectively. In the present embodiment, the LED light bulb  40   a  includes a lamp housing  12 , a bulb base  16  connected to the lamp housing  12 , a stem  19 , and a single LED filament  100 . Moreover, the LED light bulb  40   a  and the single LED filament  100  disposed in the LED light bulb  40   a  can refer to related descriptions of the previous embodiments, wherein the same or similar components and the connection relationship between components is no longer detailed. 
     In the present embodiment, the stem  19  is connected to the bulb base  16  and located in the lamp housing  12 , the stem  19  has a stand  19   a  extending vertically to the center of the lamp housing  12 , the stand  19   a  is located on the central axis of the bulb base  16 , or is located on the central axis of the LED light bulb  40   a . The LED filament  100  is disposed around the stand  19   a  and is located within the lamp housing  12 , and the LED filament  100  can be coupled to the stand  19   a  through a cantilever to maintain a predetermined curve and shape. Wherein a detailed description of the cantilever can be referenced to the previous embodiment and the drawings. The LED filament  100  includes two conductive electrodes  110 ,  112  at both ends, a plurality of LED sections  102 ,  104  and a plurality of conductive sections  130 . As shown in  FIG. 28A  to  FIG. 28D , in order to separate the conductive section  130  and the LED sections  102 ,  104  in the drawing, the plurality of the conductive sections  130  of the LED filament  100  is illustrated as points or small segments, which is only for the illustrations. It is easier to understand, and not for any limitation, and the subsequent embodiments are similarly to the related drawings by the point or small segment distribution of the conductive section  130  to distinguish from the LED sections  102 ,  104 . As described in various previous embodiments, each of the LED sections  102 ,  104  can include a plurality of LED chips connected to each other, and each of the conductive sections  130  can include a conductor. Each conductive section  130  is located between adjacent two LED sections  102 ,  104 . The conductors in each conductive section  130  connect the LED chips in the adjacent two LED sections  102 ,  104 , and the LED chips in the two LED sections  102  adjacent to the two conductive electrodes  110 ,  112  are respectively connected to the two conductive electrodes  110 ,  112 . The stem  19  can be connected to the two conductive electrodes  110 ,  112  by means of conductive brackets, details of the conductive brackets can be referred to the previous embodiment and the drawings. 
     As shown in  FIG. 28A  to  FIG. 28D , the LED filament  100  comprises two first conductive sections  130 , one second conductive sections  130 ′, and four LED sections  102 ,  104 , and every two adjacent LED sections  102 ,  104  are connected through the bending first and second conductive section  130 ,  130 ′. Moreover, since the first and second conductive sections  130 ,  130 ′ have better bendability than that of the LED sections  102 ,  104 , the first and second conductive sections  130 ,  130 ′ between the two adjacent LED sections  102 ,  104  can be bent severely, so that the angle between the two adjacent LED sections  102 ,  104  can be smaller, for example, the included angle can reach 45 degrees or less. In the present embodiment, each LED section  102 ,  104  is slightly curved or not bent compared to the first and second conductive sections  130 ,  130 ′, so that a single LED filament  100  in the LED light bulb  40   a  can be bent severer because of the first and second conductive sections  130 ,  130 ′, and the curling change in bending is more significant. Moreover, the LED filament  100  can be defined as a piece following each bending conductive sections  130 ,  130 ′, and each LED section  102 ,  104  is formed into a respective piece. 
     As shown in  FIG. 28B  and  FIG. 28C , each of the first and second conductive sections  130 ,  130 ′ and the two adjacent LED sections  102 ,  104  is composed to form a U-shaped or V-shaped bent structure, that is, the U-shaped or V-shaped bent structure formed by each of the first and second conductive sections  130 ,  130 ′ and the adjacent two LED sections  102 ,  104  is bent with two pieces, and the two LED sections  102 ,  104  are respectively formed the two pieces. In the present embodiment, the LED filament  100  is bent into four pieces by the first and second conductive sections  130 ,  130 ′, the four LED sections  102 ,  104  are respectively formed the four pieces. Also, the number of LED sections  102 ,  104  is one more than the number of the conductive sections  130 ,  130 ′. 
     As shown in  FIG. 28B , in the present embodiment, the conductive electrodes  110 ,  112  are located between the highest point and the lowest point of the LED filament  100  in the Z direction. The highest point is located at the highest first conductive section  130  in the Z direction, and the lowest point is located at the lowest second conductive section  130 ′ in the Z direction. The lower second conductive section  130 ′ and the higher first conductive section  130  are defined with the conductive electrodes  110 ,  112  as being close to or away from the bulb base  16 . Referring to  FIG. 28B , in the YZ plane, the positions of the conductive electrodes  110 ,  112  may constitute a line LA showing with dotted line, there are two first conductive sections  130  above the line LA, and one second conductive sections  130 ′ below the line LA. In other words, in the Z direction, the number of the first conductive sections  130  positioned above the line LA to which the conductive electrodes  110 ,  112  are connected may be one more than the number of the second conductive section  130 ′ positioned below the line LA. It is also contemplated that relative to the conductive electrodes  110 ,  112  as a whole, the number of the first conductive sections  130  away from the bulb base  16  is one more than the number of the second conductive section  130 ′ near the bulb base  16 . Further, if the LED filament  100  is projected on the YZ plane (refer to  FIG. 28B ), the line LA connected by the conductive electrodes  110 ,  112  has at least one intersection with the projection of the LED sections  102 ,  104 . In the YZ plane, the lines LA connected by the conductive electrodes  110 ,  112  respectively intersect the projections of the two LED sections  104 , so that the line LA and the projection of the adjacent two LED sections  104  have two intersections. 
     As shown in  FIG. 28C , if the LED filament  100  is projected on the XZ plane, the projections of the opposing two LED sections  102 ,  104  overlap each other. In some embodiments, the projections of the opposing two LED sections  102 ,  104  on a particular plane may be parallel to each other. 
     As shown in  FIG. 28D , if the LED filament  100  is projected on the XY plane, the projections of the conductive electrodes  110 ,  112  on the XY plane can be connected in a straight line LB showing with dotted line, and the projections of the first and second conductive sections  130 , 130 ′ on the XY plane are not intersected or overlapped with the line LB, and the projections of the first and second conductive sections  130 ,  130 ′ on the XY plane are respectively located on one side of the line LB. For example, as showing in  FIG. 28D , the projections of the first conductive sections  130  on the XY plane are above the line LB. 
     As shown in  FIGS. 28B to 28D , in the present embodiment, and the projection lengths of the LED filament  100  on the projection planes perpendicular to each other can have a designed proportion, so that the illumination is more uniform. For example, the projection of the LED filament  100  on the first projection surface, such as the XY plane, has a length L1, the projection of the LED filament  100  on the second projection surface, such as the YZ plane, has a length L2, and the projection of the LED filament  100  on the third projection planes, such as the XZ plane, has a length L3. The first projection plane, the second projection plane and the third projection plane are perpendicular to each other, and the normal line of the first projection plane is parallel to the axis of the LED light bulb  40   a  from the center of the lamp housing  12  to the center of the bulb base  16 . Further, the projection of the LED filament  100  on the XY plane as shown in  FIG. 28D , and the projection thereof will be similar to an inverted and deformed U shape, and the total length of the projection of the LED filament  100  on the XY plane is the length L1. The projection of the LED filament  100  on the YZ plane as shown in  FIG. 28B , the projection thereof will be similar to the inverted and deformed W shape, and the total length of the projection of the LED filament  100  on the YZ plane is the length L2. The projection of the LED filament  100  on the XZ plane can be as shown in  FIG. 28C , the projection of which will be similar to an inverted V shape, and the total length of the projection of the LED filament  100  on the XZ plane is the length L3. In the present embodiment, the length L1, the length L2, and the length L3 are approximately in a ratio of 1:1:0.9. In some embodiments, the length L1, the length L2, and the length L3 are approximately in a ratio of 1:(0.5 to 1):(0.6 to 0.9). For example, if the ratio of the length L1, the length L2, and the length L3 is closer to 1:1:1, the illumination uniformity of the single LED filament  100  in the LED light bulb  40   a  is better, and the omni-directional light appearance is better. 
     In some embodiments, the projected length of the LED filament  100  in the XZ plane or in the YZ plane is, for example but not limited thereto, a minimum of the height difference between the first conductive section  130  and the second conductive section  130 ′ in the Z direction multiply by the number of LED sections  102 ,  104 , or a minimum of the height difference of the LED filament  100  in the Z direction multiply by the number of LED sections  102 ,  104 . In the present embodiment, the total length of the LED filament  100  is about 7 to 9 times the total length of the first conductive section  130  or the second conductive section  130 ′. 
     In the present embodiment, the LED filament  100  can be bent at the positions of the first and second conductive sections  130 ,  130 ′ to form various curves, so that not only the overall aesthetic appearance of the LED light bulb  40   a  can be increased but also the light emitting of the LED light bulb  40   a  can be more uniform, and the better illumination is achieved. 
     Referring to  FIGS. 29A to 29D ,  FIG. 29A  is a perspective diagram of an LED light bulb  40   b  according to an embodiment of the present invention, and  FIGS. 29B to 29D  are respectively side views, another side view, and top view of the  FIG. 29A . In the present embodiment, the LED light bulb  40   b  includes a lamp housing  12 , a bulb base  16  connected to the lamp housing  12 , a stem  19 , a stand  19   a , and a single LED filament  100 . The LED filament  100  includes two conductive electrodes  110 ,  112  disposed at two ends, a plurality of LED sections  102 ,  104  and a plurality of the first and second conductive sections  130 ,  130 ′. Moreover, the LED light bulb  40   b  and the LED filament  100  disposed in the LED light bulb  40   b  may refer to related descriptions of the previous embodiments, wherein the same or similar components and the connection relationship between components is no longer detailed. 
     As shown in  FIG. 29A  to  FIG. 29D , the LED filament  100  comprises three first conductive sections  130 , two second conductive sections  130 ′ of, and six LED sections  102 ,  104 , and every two adjacent LED sections  102 ,  104  are connected through the bending first or second conductive sections  130 ,  130 ′. Therefore, a single LED filament  100  in the LED light bulb  40   b  can be bent severer because of the first and second conductive sections  130 ,  130 ′, and the curling modification in bending is more significant. Moreover, the LED filament  100  can be defined as having a plurality of sections, each of the sections is connected between the first and second conductive sections  130 ,  130 ′, and each LED section  102 ,  104  is formed into a respective section. In the present embodiment, the LED filament  100  is bent into six sections by the three first conductive sections  130  and the two second conductive sections  130 ′, wherein the six LED sections  102 ,  104  are respectively the six pieces. 
     Referring to  FIG. 29A  and  FIG. 29B , in the present embodiment, the height of the upper three first conductive sections  130  may be greater than the height of the other lower two second conductive sections  130 ′ in the Z direction. The height of the four LED sections  102 ,  104  is between the upper first conductive section  130  and the lower second conductive section  130 ′ in the Z direction. The other two LED sections  102 ,  104  extend downward from the corresponding first conductive section  130  in the Z direction, and the height of the conductive electrodes  110 ,  112  is less than the height of the first conductive section  130  in the Z direction. As shown in  FIG. 29C  of the present embodiment, the projections of the opposite LED sections  102 ,  104  are overlapped each other when the LED filament  100  is projected on the XZ plane. In the embodiment as shown in  FIG. 29D , when the LED filament  100  is projected on the XY plane, the projections of all the second conductive sections  130 ′ are located in one side of a straight line connecting between the conductive electrodes  110 ,  112 , and the projections of the first conductive section  130  is dispersed on both sides of the straight line connecting between the conductive electrodes  110 ,  112 . 
     Referring to  FIGS. 30A to 30D ,  FIG. 30A  is a perspective diagram of an LED light bulb  40   c  according to an embodiment of the present invention, and  FIGS. 30B to 30D  are respectively side view, another side view, and top view of the  FIG. 30A . In the present embodiment, the LED light bulb  40   c  includes a lamp housing  12 , a bulb base  16  connected to the lamp housing  12 , a stem  19 , a stand  19   a , and a single LED filament  100 . The LED filament  100  includes two conductive electrodes  110 ,  112  disposed at two ends, a plurality of LED sections  102 ,  104  and a plurality of first and second conductive sections  130 ,  130 ′. Moreover, the LED light bulb  40   c  and the single LED filament  100  disposed in the LED light bulb  40   c  can refer to related descriptions of the previous embodiments, wherein the same or similar components and the connection relationship between components is no longer detailed. 
     As shown in  FIG. 30A  to  FIG. 30D , the LED filament  100  comprises three first conductive sections  130  and four second conductive sections  130 ′, and eight LED sections  102 ,  104 , and every two adjacent LED sections  102 ,  104  are connected by the bending first or second conductive sections  130 ,  130 ′. Therefore, the single LED filament  100  in the LED light bulb  40   c  can be bent severer because of the first and second conductive sections  130 ,  130 ′, and the curling change in bending is more significant. Moreover, the LED filament  100  can be defined as having a plurality of sections, each of the sections is connected between the first and second conductive sections  130 ,  130 ′, and each LED section  102 ,  104  is formed into a respective section. In the present embodiment, the LED filament  100  is bent into eight sections by the three first conductive sections  130  and the four second conductive sections  130 ′, wherein the eight LED sections  102 ,  104  are respectively the eight sections. 
     Referring to  FIG. 30A  and  FIG. 30B , in the present embodiment, the height of the upper three first conductive sections  130  may be greater than the height of the other lower four second conductive sections  130 ′ in the Z direction. The height of the six LED sections  102 ,  104  is between the upper first conductive section  130  and the lower second conductive section  130 ′ in the Z direction. The other two LED sections  102 ,  104  extend upward from the corresponding second conductive section  130 ′ in the Z direction, and the height of the conductive electrodes  110 ,  112  is approximately equal to the height of the upper first conductive section  130  in the Z direction. As shown in  FIG. 30B  and  FIG. 30C  of the present embodiment, the projections of the opposite LED sections  102 ,  104  are overlapped each other when the LED filament  100  is projected on the YZ plane (referring to  FIG. 30B ) or XZ plane (referring to  FIG. 30C ). In the embodiment as shown in  FIG. 30D , when the LED filament  100  is projected on the XY plane, all the projections of the first and second conductive sections  130 ,  130 ′ are located in one side of a straight line connecting between the conductive electrodes  110 ,  112 . 
     Referring to  FIGS. 31A to 31D ,  FIG. 31A  is a perspective diagram of an LED light bulb  40   d  according to an embodiment of the present invention, and  FIGS. 31B to 31D  are respectively side view, another side view, and top view of the  FIG. 31A . In the present embodiment, the LED light bulb  40   d  includes a lamp housing  12 , a bulb base  16  connected to the lamp housing  12 , a stem  19 , a stand  19   a , and a single LED filament  100 . The LED filament  100  includes two conductive electrodes  110 ,  112  at two ends, a plurality of LED sections  102 ,  104  and a plurality of first and second conductive sections  130 ,  130 ′. Moreover, the LED light bulb  40   d  and the single LED filament  100  disposed in the LED light bulb  40   d  can refer to related descriptions of the previous embodiments, wherein the same or similar components and the connection relationship between components is no longer detailed. 
     As shown in  FIG. 31A  to  FIG. 31D , the LED filament  100  comprises two first conductive sections  130  and one second conductive section  130 ′, and four LED sections  102 ,  104 , and every two adjacent LED sections  102 ,  104  are connected by the bending first or second conductive sections  130 ,  130 ′. Therefore, the single LED filament  100  in the LED light bulb  40   d  can be bent severer because of the first and second conductive sections  130 ,  130 ′, and the curling change in bending is more significant. Moreover, the LED filament  100  can be defined as having a plurality of sections, each of the sections is connected between the first and second conductive sections  130 ,  130 ′, and each LED section  102 ,  104  is formed into a respective section. In the present embodiment, the LED filament  100  is bent into four sections by two first conductive sections  130  and one second conductive sections  130 ′, wherein the four LED sections  102 ,  104  are respectively the four sections. 
     Referring to  FIG. 31A ,  FIG. 31B  and  FIG. 31C , in the present embodiment, the height of the upper two first conductive sections  130  may be greater than the height of the second conductive sections  130 ′ in the Z direction. The height of the two LED sections  102 ,  104  is between the upper first conductive section  130  and the lower second conductive section  130 ′ in the Z direction. The other two LED sections  102 ,  104  extend downward from the corresponding first conductive section  130  in the Z direction, and the height of the conductive electrodes  110 ,  112  is less than the height of the second conductive section  130 ′ in the Z direction. As shown in  FIG. 31C  of the present embodiment, the projections of the opposite LED sections  102 ,  104  are overlapped each other when the LED filament  100  is projected on the XZ plane. In the embodiment as shown in  FIG. 31D , when the LED filament  100  is projected on the XY plane, all the projections of the first and second conductive sections  130 ,  130 ′ are located in one side of a straight line connecting between the conductive electrodes  110 ,  112 . 
     Compared to the LED filament  100  of the LED light bulb  40   a  shown in  FIGS. 28A to 28D , the height difference between the first and second conductive sections  130 ,  130 ′ of the LED filament  100  of the LED light bulb  40   d  shown in  FIGS. 31A to 31D  is smaller in the Z direction, the bending curvature of the first and second conductive sections  130 ,  130 ′ is relatively large, so that the fluctuation curve of the LED filament  100  as a whole is tending to smaller. 
     Referring to  FIGS. 32A to 32D ,  FIG. 32A  is a perspective diagram of an LED light bulb  40   e  according to an embodiment of the present invention, and  FIGS. 32B to 32D  are respectively side view, another side view, and top view of the  FIG. 32A . In the present embodiment, the LED light bulb  40   e  includes a lamp housing  12 , a bulb base  16  connected to the lamp housing  12 , a stem  19 , a stand  19   a , and a single LED filament  100 . The LED filament  100  includes two conductive electrodes  110 ,  112  disposed at two ends, a plurality of LED sections  102 ,  104  and a plurality of first and second conductive sections  130 ,  130 ′. Moreover, the LED light bulb  40   e  and the single LED filament  100  disposed in the LED light bulb  40   e  can refer to related descriptions of the previous embodiments, wherein the same or similar components and the connection relationship between components is no longer detailed. 
     As shown in  FIG. 32A  to  FIG. 32D , the LED filament  100  comprises three first conductive sections  130  and two second conductive sections  130 ′, and six LED sections  102 ,  104 , and every two adjacent LED sections  102 ,  104  are connected by the bending first or second conductive sections  130 ,  130 ′. Therefore, the single LED filament  100  in the LED light bulb  40   e  can be bent severer because of the first and second conductive sections  130 ,  130 ′, and the curling change in bending is more significant. Moreover, the LED filament  100  can be defined as having a plurality of sections, each of the sections is connected between the first and second conductive sections  130 ,  130 ′, and each LED section  102 ,  104  is formed into a respective section. In the present embodiment, the LED filament  100  is bent into six sections by the three first conductive sections  130  and the two second conductive sections  130 ′, wherein the six LED sections  102 ,  104  are respectively the six sections. 
     Referring to  FIG. 32A ,  FIG. 32B  and  FIG. 32C , in the present embodiment, the height of the upper three first conductive sections  130  may be greater than the height of the lower two second conductive sections  130 ′ in the Z direction. The height of the four LED sections  102 ,  104  is between the upper first conductive section  130  and the lower second conductive section  130 ′ in the Z direction. The other two LED sections  102 ,  104  extend downward from the corresponding first conductive section  130  in the Z direction, and the height of the conductive electrodes  110 ,  112  is less than the height of the first conductive section  130  in the Z direction. As shown in  FIG. 32C  of the present embodiment, the projections of the opposite LED sections  102 ,  104  are overlapped each other when the LED filament  100  is projected on the XZ plane. In the embodiment as shown in  FIG. 32D , when the LED filament  100  is projected on the XY plane, the projections of the second conductive sections  130 ′ are located in one side of a straight line connecting between the conductive electrodes  110 ,  112 . 
     Compared to the LED filament  100  of the LED light bulb  40   b  shown in  FIGS. 29A to 29D , the height difference between the first and second conductive sections  130 ,  130 ′ of the LED filament  100  of the LED light bulb  40   e  of  FIGS. 32A to 32D  is smaller in the Z direction, the bending curvature of the first and second conductive sections  130 ,  130 ′ is relatively large, so that the fluctuation curve of the LED filament  100  as a whole is tending to smaller. 
     Referring to  FIGS. 33A to 33D ,  FIG. 33A  is a perspective diagram of an LED light bulb  40   f  according to an embodiment of the present invention, and  FIGS. 33B  to  33 D are respectively side view, another side view, and top view of the  FIG. 33A . In the present embodiment, the LED light bulb  40   f  includes a lamp housing  12 , a bulb base  16  connected to the lamp housing  12 , a stem  19 , a stand  19   a , and a single LED filament  100 . The LED filament  100  includes two conductive electrodes  110 ,  112  disposed at two ends, a plurality of LED sections  102 ,  104  and a plurality of first and second conductive sections  130 ,  130 ′. Moreover, the LED light bulb  40   f  and the single LED filament  100  disposed in the LED light bulb  40   f  can refer to related descriptions of the previous embodiments, wherein the same or similar components and the connection relationship between components is no longer detailed. 
     As shown in  FIG. 33A  to  FIG. 33D , the LED filament  100  comprises three first conductive sections  130  and four second conductive sections  130 ′, and eight LED sections  102 ,  104 , and every two adjacent LED sections  102 ,  104  are connected by the bending first or second conductive sections  130 ,  130 ′. Therefore, the single LED filament  100  in the LED light bulb  40   f  can be bent severer because of the first and second conductive sections  130 ,  130 ′, and the curling change in bending is more significant. Moreover, the LED filament  100  can be defined as having a plurality of sections, each of the sections is connected between the first and second conductive sections  130 ,  130 ′, and each LED section  102 ,  104  is formed into a respective sections. In the present embodiment, the LED filament  100  is bent into eight sections by three conductive sections  130  and four second conductive sections  130 ′, wherein the eight LED sections  102 ,  104  are respectively the eight sections. 
     Referring to  FIG. 33A ,  FIG. 33B  and  FIG. 33C , in the present embodiment, the height of the upper three first conductive sections  130  may be greater than the height of the lower four second conductive sections  130 ′ in the Z direction. The height of the six LED sections  102 ,  104  is between the upper first conductive section  130  and the lower second conductive section  130 ′ in the Z direction. The other two LED sections  102 ,  104  extend upward from the corresponding second conductive section  130 ′ in the Z direction, and the height of the conductive electrodes  110 ,  112  is approximately equal to the height of the upper second conductive section  130 ′ in the Z direction. As shown in  FIG. 33B  and  FIG. 33C  of the present embodiment, the projections of the opposite LED sections  102 ,  104  are overlapped each other when the LED filament  100  is projected on the YZ plane (referring to  FIG. 33B ) or the XZ plane (referring to  FIG. 33C ). In the embodiment as shown in  FIG. 33D , when the LED filament  100  is projected on the XY plane, all the projections of the first and second conductive sections  130 ,  130 ′ are located in one side of a straight line connecting between the conductive electrodes  110 ,  112 . 
     Compared to the LED filament  100  of the LED light bulb  40   c  shown in  FIGS. 30A to 30D , the height difference between the first and second conductor sections  130 ,  130 ′ of the LED filament  100  of the LED light bulb  40   f  shown in  FIGS. 33A to 33D  is smaller in the Z direction, the bending curvature of the first and second conductive sections  130 ,  130 ′ is relatively large, so that the fluctuation curve of the LED filament  100  as a whole is tending to smaller. 
     Referring to  FIGS. 34A to 34D ,  FIG. 34A  is a perspective diagram of an LED light bulb  40   g  according to an embodiment of the present invention, and  FIGS. 34B to 34D  are respectively side view, another side view, and top view of the  FIG. 34A . In the present embodiment, the LED light bulb  40   g  includes a lamp housing  12 , a bulb base  16  connected to the lamp housing  12 , a stem  19 , a stand  19   a , and a single LED filament  100 . The LED filament  100  includes two conductive electrodes  110 ,  112  disposed at two ends, a plurality of LED sections  102 ,  104  and a plurality of first and second conductive sections  130 ,  130 ′. Moreover, the LED light bulb  40   g  and a single LED filament  100  disposed in the LED light bulb  40   g  can refer to related descriptions of the previous embodiments, wherein the same or similar components and the connection relationship between components is no longer detailed. 
     As shown in  FIG. 34A  to  FIG. 34D , the LED filament  100  comprises two conductive sections  130 , one second conductive section  130 ′, and four LED sections  102 ,  104 , and every two adjacent LED sections  102 ,  104  are connected by the bending first and second conductive sections  130 ,  130 ′. Therefore, the single LED filament  100  in the LED light bulb  40   g  can be bent severer because of the first and second conductive sections  130 ,  130 ′, and the curling change in bending is more significant. Moreover, the LED filament  100  can be defined as having a plurality of sections, each of the sections is connected between the first and second conductive sections  130 ,  130 ′, and each LED section  102 ,  104  is formed into a respective section. In the present embodiment, the LED filament  100  is bent into four sections by the two conductive sections  130  and the one second conductive section  130 ′, wherein the four LED sections  102 ,  104  are respectively the four sections. 
     Referring to  FIG. 34A ,  FIG. 34B  and  FIG. 34C , in the present embodiment, the height of the upper two first conductive sections  130  may be greater than the height of the lower one second conductive sections  130 ′ in the Z direction. The height of the two LED sections  104  is between the upper first conductive section  130  and the lower second conductive section  130 ′ in the Z direction. The other two LED sections  102 ,  104  extend downward from the corresponding first conductive section  130  in the Z direction, and the height of the conductive electrodes  110 ,  112  is less than the height of the second conductive section  130 ′ in the Z direction. 
     In the present embodiment as shown in  FIG. 34A , the LED filament  100  extends around an axial direction and is resulted of a curling posture similar to spiral-like. As shown in  FIG. 34B , the diameter of the spiral-like intermediate coil of the LED filament  100  (ie, the portion around which the two LED sections  102 ,  104  are formed) is relatively small, and the diameter of the outer spiral-like coil of the LED filament  100  (ie, the portion of the other two LED sections  102 ,  104  that extends outwardly and connects respectively with the conductive electrodes  110 ,  112 ) is relatively large. Moreover, the contour of the LED filament in the YZ plane may form a heart-like shape, and the distance between the two first conductive sections  130  is less than the distance between the two conductive electrodes  110 ,  112  in the Y direction. In other embodiments, the distance between the two first conductive sections  130  may be greater than or equal to the distance between the two conductive electrodes  110 ,  112  in the Y direction. In the present embodiment as shown in  FIG. 34C , the LED filament  100  is in a shape like deformed S letter in the XZ plane. If the length of the LED filament  100  continues extending in a spiral-like posture along its axial direction, the curling posture of the LED filament  100  may have a plurality of overlapping shapes like deformed S letter in the XZ plane. In the present embodiment as shown in  FIG. 34D , the curling posture of the LED filament  100  also has a shape like deformed S letter in the XY plane. If the length of the LED filament  100  continues extending in a spiral-like posture along its axial direction, the curling posture of the LED filament  100  may have a plurality of overlapping shapes like deformed S letter in the XY plane. As shown in  FIGS. 34C and 34D , in the present embodiment, the first and second conductive sections  130 ,  130 ′ are located between the conductive electrodes  110 ,  112 . 
     Referring to  FIGS. 35A to 35D ,  FIG. 35A  is a perspective diagram of an LED light bulb  40   h  according to an embodiment of the present invention, and  FIGS. 35B to 35D  are respectively side view, another side view, and top view of the  FIG. 35A . In the present embodiment, the LED light bulb  40   h  includes a lamp housing  12 , a bulb base  16  connected to the lamp housing  12 , a stem  19 , a stand  19   a , and a single LED filament  100 . The LED filament  100  includes two conductive electrodes  110 ,  112  at two ends, a plurality of LED sections  102 ,  104  and a single conductive section  130 . Moreover, the LED light bulb  40   h  and the single LED filament  100  disposed in the LED light bulb  40   h  can refer to related descriptions of the previous embodiments, wherein the same or similar components and the connection relationship between components is no longer detailed. 
     Referring to  FIGS. 35A to 35D , in the present invention, the LED filament section  100  includes one conductive section  130 , two LED sections  102 ,  104 , and between two adjacent LED sections  102 ,  104  is connected by the conductive section  130 . Wherein the LED filament  100  having a circular arc at the highest point of the bending curvature, that is, each of the LED sections  102 ,  104  respectively having a circular arc at the highest point of the LED filament  100 , and the conductive section also exhibits a circular arc at the low point of the LED filament. Moreover, the LED filament  100  can be defined as having a plurality of sections, each of the sections is connected between the first and second conductive sections  130 , and each LED section  102 ,  104  is formed into a respective section. 
     Moreover, since the LED filament  100  is equipped with a flexible base layer, the flexible base layer preferably is made by an organosilicon-modified polyimide resin composition, and thus the LED sections  102 ,  104  themselves also have a certain degree of bendability. In the present embodiment, the two LED sections  102 ,  104  are respectively bent to form in the shape like an inverted deformed U letter, and the conductive section  130  is located between the two LED sections  102 ,  104 , and the degree of the bending of the conductive section  130  is the same as or greater than the degree of the bending of the LED sections  102 ,  104 . In other words, the two LED sections  102 ,  104  of the LED filament are respectively bent at the high point to form in the shape like an inverted deformed U letter and have a bending radius value at R1, and the conductive section  130  is bent at a low point of the LED filament  100  and has a bending radius value at R2, wherein the value R1 is the same as or greater than the value R2. Through the configuration of the conductive section  130 , the LED filament  100  disposing in a limited space can be realized with a small radius bending of the LED filament  100 . In one embodiment, the bending points of the LED sections  102 ,  104  are at the same height in the Z direction. Further, in the Z direction, the stand  19   a  of the present embodiment has a lower position than the stand  19   a  of the previous embodiment, and the height of the present stand  19   a  is corresponding to the height of the conductive section  130 . For example, the lowest portion of the conductive section  130  can be connected to the top of the stand  19   a  so that the overall shape of the LED filament  100  is not easily deformed. In various embodiments, the conductive sections  130  may be connected to the stand  19   a  through the perforation of the top of the stand  19   a , or the conductive sections  130  may be glued to the top of the stand  19   a  to connect with each other, but are not limited thereto. In an embodiment, the conductive section  130  and the stand  19   a  may be connected by a guide wire, for example, a guide wire connected to the conductive section  130  is drawn at the top of the stand  19   a.    
     As shown in  FIG. 35B , in the present embodiment, the height of the conductive section  130  is higher than the two conductive electrodes  110 ,  112  in the Z direction, and the two LED sections  102 ,  104  are respectively shaped upward from the two conductive electrodes  110 ,  112  to the highest point and then are bent down to connect with the conductive section  130 . As shown in  FIG. 35C , in the present embodiment, the contour of the LED filament  100  in the XZ plane is similar to the V letter, that is, the two LED sections  102 ,  104  are respectively shaped obliquely upward and outward and are bent respectively at the highest point and then obliquely inwardly to connect with the conductive section  130 . As shown in  FIG. 35D , in the present embodiment, the LED filament  100  has a contour in the shape like S letter in the XY plane. As shown in  FIG. 35B  and  FIG. 35D , in the present embodiment, the conductive section  130  is located between the conductive electrodes  110 ,  112 . As shown in  FIG. 35D , in the XY plane, the main bending points of the LED sections  102 ,  104 , and the conductive electrodes  110 ,  112  are substantially on the circumference centered on the conductive section  130 . 
     Referring to  FIG. 36 , which is a schematic diagram of the light emission spectrum of an LED light bulb according to an embodiment of the present invention. In the present embodiment, the LED light bulb may be any of the LED light bulbs disclosed in the previous embodiments, and any one of the LED light bulbs disclosed in the previous embodiments is provided. The light emitted by the LED light bulb is measured by a spectrometer to obtain a spectrum diagram as shown in  FIG. 36 . From the spectrum diagram, the spectral distribution of the LED light bulb is mainly between the wavelength ranges of about 400 nm to 800 nm. Moreover, there are three peaks of intensity values P1, P2, P3 in wavelength ranges corresponding to the light emitted by the LED light bulb. The wavelength of the intensity value P1 is between about 430 nm and 480 nm, the wavelength of the intensity value P2 is between about 580 nm and 620 nm, and the wavelength of the intensity value P3 is between about 680 nm and 750 nm. The light intensity of the peak P1 is less than that of the peak P2, and the light intensity of the peak P2 is less than the light intensity of the peak P3. As shown in  FIG. 36 , such a spectral distribution is close to the spectral distribution of a conventional incandescent filament lamp and also close to the spectral distribution of natural light. In accordance with an embodiment of the present invention, a schematic diagram of the light emission spectrum of a single LED filament is shown in  FIG. 37 . From the spectrum diagram, it can be seen that the spectral distribution of the LED light bulb is mainly between the wavelength range of about 400 nm to 800 nm, and there are three peaks of intensity values P1, P2, P3 in that wavelength range. The wavelength of the intensity value P1 is between about 430 nm and 480 nm, the wavelength of the intensity value P2 is between about 480 nm and 530 nm, and the wavelength of the intensity value peak P3 is between about 630 nm and 680 nm. Such a spectral distribution is close to the spectral distribution of a conventional incandescent filament lamp and also close to the spectral distribution of natural light. 
     The meaning of the term “a single LED filament” and “a single strip LED filament” as used in the present invention is mainly composed of the aforementioned conductive section, the LED section, the connection between thereof, the light conversion layer (including the consecutive top layer or the bottom layer, with continuous formation to cover or support all the components), and two conductive electrodes electrically connected to the conductive brackets of the LED light bulb disposing at both ends of the LED filament, which is the single LED filament structure referred to in the present invention. 
     In some embodiments, LED filament  100  may have multiple LED sections. At least part or all of LED chips on a single LED section are electrically connected in series. Different LED sections are electrically connected in parallel. Anode and cathode of each LED section may serve as a positive electrode and negative electrodes of the LED filament, respectively. The negative electrodes separately connect with two or more of the conductive supports (e.g., conductive supports  51   a ,  51   b  in  FIG. 26A ) and finally connect to a power module (such as power module  518  in  FIG. 26A ). As shown in  FIG. 38A , which is a schematic circuit diagram of the LED filament according to some embodiments of the present invention, LED filament  100  in this embodiment has two LED sections  402 ,  404 . Each LED section  402 ,  404  includes one or more LED chips. LED chips in a single LED section are electrically connected in series. Two LED sections  402 ,  404  have respective current paths after they have been electrically electrically connected (i.e. in parallel). In detail, in this embodiment, anodes of LED sections  402 ,  404  are electrically connected together to serve as a positive electrode P1 of LED filament  100 . Cathodes of LED section  402  and  404  serve as a first negative electrode N1 and a second negative electrode N2, respectively. Positive electrode P1, first negative electrode N1 and second negative electrode N2 are separately electrically connected to the power module through conductive supports such as conductive supports  51   a ,  51   b  and power module  518  shown in  FIG. 26A . 
     In more detail, the connection relationship between positive electrode P1, first negative electrode N1 and second negative electrode N2 may be shown as  FIG. 38B  or  FIG. 38C , in which  FIGS. 38B and 38C  are two schematic views of electrical connections of the LED filament according to some embodiments of the present invention. Please refer to  FIG. 38B  first. In this embodiment, positive electrode P1 of LED filament  100  is electrically connected to a first output terminal (also called “positive output terminal) of power module  518 . First and second negative electrodes N1, N2 of LED filament  100  are electrically connected together and then jointly electrically connected to a second output terminal (also called “negative output terminal”) of power module  518 . Further refer to  FIG. 38A , under the electrical relationship shown in  FIG. 38B , LED sections  402 ,  404  can be deemed as being electrically connected to the output terminals of power module  518  in parallel. Thus, all LED sections  402 ,  404  are driven by driving voltage V1 between the first and second output terminals. Under a precondition of LED sections  402 ,  404  having identical or similar chips number and arrangement, the driving current from power module  518  will evenly dividedly flow to each of LED sections  402 ,  404 . As a result, LED sections  402 ,  404  can present approximately even intensity and/or color temperature. 
     Please further refer to  FIG. 38C . In this embodiment, positive electrode P1 of LED filament  100  is electrically connected to the first output terminal of power module  518 , first negative electrode N1 of LED filament  100  is electrically connected to the second output terminal (also called “first negative output terminal”) of power module  518 , and the second negative electrode N2 of LED filament  100  is electrically connected to the third output terminal (also called “second negative output terminal”) of power module  518 . Driving voltage V1 is formed between the first output terminal and the second output terminal of power module  518 , and another driving voltage V2 is formed between the first output terminal and the third output terminal of power module  518 . Referring to  FIG. 38A  together, under the electrical relationship shown in  FIG. 38C , LED section  402  is electrically connected between the first output terminal and the second output terminal, and LED section  404  is electrically connected between the first output terminal and the third output terminal. As a result, LED sections  402  and  404  can be deemed as being driven by driving voltages V1, and V2, respectively. In such an arrangement, the driving currents provided by power module  518  to LED sections  402 ,  404  can be independently controlled by adjusting output voltages V1 and V2, so as to make LED sections  402 ,  404  separately generate corresponding intensity and/or color temperature. In other words, dimming the different LED sections individually on a single LED filament can be implemented by design and control of the power module based on the arrangement of  FIG. 38C . 
     In some embodiments, the second and third output terminals of power module  518  can be electrically connected together through a resistor, and either of the second and third output terminals of the power module  518  is electrically connected to a ground terminal. By this arrangement, negative output terminals with different levels can be obtained to generate two different driving voltages V1 and V2. In some embodiments, levels of the second and third output terminals can be controlled by a circuit. The present invention is not limited thereto. 
       FIG. 39A  is a schematic circuit diagram of the LED filament according to some embodiments of the present invention. In this embodiment, LED filament  100 , which is similar to the one shown in  FIG. 38A , has two LED sections  402 ,  404 , and thus the details of the LED sections  402 ,  404  will not be repeated herein. A main difference between this embodiment and the embodiment shown in  FIG. 38A  is that cathodes of LED sections  402 ,  404  of this embodiment are electrically connected together to serve as negative electrode N1 of the LED filament, and anodes of LED sections  402 ,  404  serve as first positive electrode P1 and second positive electrode P2 of LED filament  100 , respectively. Negative electrode N1, first positive electrode P1 and second positive electrode P2 of LED filament  100  are electrically connected to the power module through conductive supports, such as conductive supports  51   a ,  51   b  and power module  518  shown in  FIG. 26A . 
     The electrical relationship between negative electrode N1, first positive electrode P1 and second positive electrode P2 of LED filament  100  and the power module may be shown in  FIG. 39B or 39C .  FIGS. 39B and 39C  are two schematic views of electrical connections of the LED filament according to two different embodiments. Please refer to  FIG. 39B  first. In this embodiment, a first positive electrode P1 and a second positive electrode P2 of LED filament  100  are electrically electrically connected together and jointly electrically connected to a first output terminal (also called “positive output terminal) of power module  518 . Negative electrode N1 of LED filament  100  is electrically connected to a second output terminal (also called “negative output terminal”) of power module  518 . Further refer to  FIG. 39A , under the electrical relationship shown in  FIG. 39B , LED sections  402 ,  404  can be deemed as being electrically connected to the output terminals of power module  518  in parallel. Thus, all LED sections  402 ,  404  are driven by driving voltage V1 between the first and second output terminals. Under a precondition of LED sections  402 ,  404  having identical or similar chips number and arrangement, the driving current from power module  518  will evenly dividedly flow to each of LED sections  402 ,  404 . As a result, LED sections  402 ,  404  can present approximately even intensity and/or color temperature. This arrangement is equivalent to that of the embodiment shown in  FIG. 38B . 
     Please further refer to  FIG. 39C . In this embodiment, positive electrode P1 of LED filament  100  is electrically connected to the first output terminal of power module  518 , second positive electrode P2 of LED filament  100  is electrically connected to the second output terminal (also called “second positive output terminal”) of power module  518 , and negative electrode N1 of LED filament  100  is electrically connected to the third output terminal (also called “negative output terminal”) of power module  518 . Driving voltage V1 is formed between the first output terminal and the third output terminal of power module  518 , and another driving voltage V2 is formed between the second output terminal and the third output terminal of power module  518 . Please further refer to  FIG. 39A . Under the electrical relationship shown in  FIG. 39C , LED section  402  is electrically connected between the first output terminal and the third output terminal, and LED section  404  is electrically connected between the second output terminal and the third output terminal. As a result, LED sections  402  and  404  can be deemed as being driven by driving voltages V1, and V2, respectively. In such an arrangement, the driving currents provided by power module  518  to LED sections  402 ,  404  can be independently controlled by adjusting output voltages V2, V2 so as to make LED sections  402 ,  404  separately generate corresponding intensity and/or color temperature. In other words, in the arrangement of  FIG. 39C , a dimming function can be implemented to a single LED filament by design and control of the power module. 
       FIG. 40A  is a schematic circuit diagram of the LED filament according to some embodiments of the present invention. In this embodiment, LED filament  100  has three LED sections  402 ,  404 ,  406  as shown in  FIG. 40A . In detail, LED filament  100  of this embodiment is based on  FIG. 38A  and adds LED section  406  (also deemed as being based on  FIG. 39A  and adding LED section  404  in  FIG. 40A , wherein LED section  406  in  FIG. 40A  corresponds to LED section  404  in  FIG. 39A ). The arrangement of LED sections  402 ,  404  can refer to the above embodiments, it will not be repeated here. In this embodiment, the arrangement of LED section  406 , which is identical or similar to that of LED section  402  or  404 , includes one or more LED chips. The LED chips are electrically connected in series. Three LED sections  402 ,  404 ,  406  have respective current paths after they have been electrically connected (i.e. in parallel). In detail, in this embodiment, cathodes of LED sections  406  and  402  are electrically connected together (i.e. cathodes of LED sections  402 ,  406  jointly serve as a first negative electrode N1). And anode of LED section  406  serves as a second positive electrode P2 of LED filament  100 . In other words, In this embodiment, LED filament  100  further includes second positive electrode P2 formed by connecting to the anode of LED section  406  other than first positive electrode P1, first negative electrode N1 and second negative electrode N2. 
     In this embodiment, under the arrangement of LED filament  100 , the electrical relationship between LED filament  100  and the power module may be shown in  FIGS. 40B to 40D  to implement the current sharing drive control or sectional independent control.  FIGS. 39B and 39C  are two schematic views of electrical connections of two embodiments of the LED filament. Please refer to  FIG. 39B  first. In this embodiment, a first positive electrode P1 and a second positive electrode P2 of LED filament  100  are electrically connected together and jointly electrically connected to a first output terminal (also called “positive output terminal) of power module  518 . First negative electrode N1 and second negative electrode N2 of LED filament  100  are electrically connected together and electrically connected to a second output terminal (also called “negative output terminal”) of power module  518 . Further refer to  FIG. 40A , under the electrical relationship shown in  FIG. 40B , LED sections  402 ,  404 ,  406  can be deemed as being electrically connected to the output terminals of power module  518  in parallel. Thus, all LED sections  402 ,  404 ,  406  are driven by driving voltage V1 between the first and second output terminals. Under a precondition of LED sections  402 ,  404 ,  406  having identical or similar chips number and arrangement, the driving current from power module  518  will evenly dividedly flow to each of LED sections  402 ,  404 ,  406 . As a result, LED sections  402 ,  404 ,  406  can present approximately even intensity and/or color temperature. This arrangement is equivalent to that of the embodiment shown in  FIGS. 38B and 39B . 
     Please further refer to  FIG. 40C . In this embodiment, first positive electrode P1 and second positive electrode P2 of LED filament  100  are electrically connected together and jointly electrically connected to the first output terminal (also called “first positive output terminal”) of power module  518 , first negative electrode N1 of LED filament  100  is electrically connected to the second output terminal (also called “first negative output terminal”) of power module  518 , and second negative electrode N2 of LED filament  100  is electrically connected to the third output terminal (also called “second negative output terminal”) of power module  518 . Under such an arrangement, both first positive electrode P1 and second positive electrode P2 can be deemed as the same terminal. Thus, the whole circuit is equivalent to  FIG. 38C . Related control manner, functions and effects can refer to the description of  FIG. 38C . The arrangement of this embodiment can make a single filament have a two-stage dimming effect. 
     Please further refer to  FIG. 40D . In this embodiment, first positive electrode P1 of LED filament  100  is electrically connected to the first output terminal (also called “first positive output terminal”) of power module  518 , second positive electrode P2 of LED filament  100  is electrically connected to the second output terminal (also called “second positive output terminal”) of power module  518 , first negative electrode N1 of LED filament  100  is electrically connected to the third output terminal (also called “first negative output terminal”), and second negative electrode N2 is electrically connected to fourth output terminal (also called “second negative output terminal”) of power module  518 . Further refer to  FIG. 40A , under such an arrangement shown in  FIG. 40D , LED section  402  is electrically connected between the first and third terminals, LED section  404  is electrically connected between the first and fourth output terminals, and LED section  406  is electrically connected between the second and third terminals. Thus, LED sections  402 ,  404 ,  406  can be deemed as being driven by driving voltages V1, V2, V3, respectively. In such an arrangement, the driving currents provided by power module  518  to LED sections  402 ,  404 ,  406  can be independently controlled by adjusting output voltages V2, V2, V3 so as to make LED sections  402 ,  404 ,  406  separately generate corresponding intensity and/or color temperature. The arrangement of this embodiment can make a single filament have a three-stage dimming effect. 
       FIG. 41A  is a schematic circuit diagram of an embodiment of the LED filament of the present invention. In this embodiment, LED filament  100  has four LED sections  402 ,  404 ,  406 ,  408  as shown in  FIG. 41A . In detail, LED filament  100  of this embodiment is based on  FIG. 40A  and further includes LED section  408 . The arrangement of LED sections  402 ,  404 ,  406  can refer to the above embodiments, it will not be repeated here. In this embodiment, the arrangement of LED section  408 , which is identical or similar to that of LED section  402 ,  404  or  406 , includes one or more LED chips. The LED chips are electrically connected in series. Three LED sections  402 ,  404 ,  406 ,  408  have respective current paths after they have been electrically connected (i.e. in parallel). In detail, cathodes of LED sections  408  and  404  are electrically connected together (i.e. cathodes of LED sections  402 ,  406  jointly serve as a second negative electrode N2). And anode of LED section  408  serves as a third positive electrode P3 of LED filament  100 . In other words, In this embodiment, LED filament  100  further includes third positive electrode P3 formed by connecting to the anode of LED section  408  other than first positive electrode P1, second positive electrode P2, first negative electrode N1 and second negative electrode N2. 
     In this embodiment, under the arrangement of LED filament  100 , the electrical relationship between LED filament  100  and the power module may be shown in  FIGS. 41B to 41E  to implement the current sharing drive control or sectional independent control.  FIGS. 41B to 41E  are four schematic views of electrical connections of four embodiments of the LED filament. Please refer to  FIG. 41B  first. In this embodiment, a first positive electrode P1, a second positive electrode P2 and a third positive electrode P3 of LED filament  100  are electrically connected together and jointly electrically connected to a first output terminal (also called “positive output terminal) of power module  518 . First negative electrode N1 and second negative electrode N2 of LED filament  100  are electrically connected together and electrically connected to a second output terminal (also called “negative output terminal”) of power module  518 . Further refer to  FIG. 41A , under the electrical relationship shown in  FIG. 41B , LED sections  402 ,  404 ,  406 ,  408  can be deemed as being electrically connected to the output terminals of power module  518  in parallel. Thus, all LED sections  402 ,  404 ,  406 ,  408  are driven by driving voltage V1 between the first and second output terminals. Under a precondition of LED sections  402 ,  404 ,  406 ,  408  having identical or similar chips number and arrangement, the driving current from power module  518  will evenly dividedly flow to each of LED sections  402 ,  404 ,  406 ,  408 . As a result, LED sections  402 ,  404 ,  406  can present approximately even intensity and/or color temperature. This arrangement is equivalent to that of the embodiment shown in  FIGS. 38B, 39B and 40B . 
     Please further refer to  FIG. 41C . In this embodiment, first positive electrode P1, second positive electrode P2 and third positive electrode P3 of LED filament  100  are electrically connected together and jointly electrically connected to the first output terminal (also called “first positive output terminal”) of power module  518 , first negative electrode N1 of LED filament  100  is electrically connected to second output terminal (also called “first negative output terminal”) of power module  518 , and second negative electrode N2 of LED filament  100  is electrically connected to the third output terminal (also called “second negative output terminal”) of power module  518 . Under such an arrangement, first positive electrode P1, second positive electrode P2 and third positive electrode P3 can be deemed as the same terminal. Thus, the whole circuit is equivalent to  FIG. 38C . Related control manner, functions and effects can refer to the description of  FIG. 38C . The arrangement of this embodiment can make a single filament have a two-stage dimming effect. 
     Please further refer to  FIG. 41D . In this embodiment, first positive electrode P1 and second positive electrode P2 of LED filament  100  are electrically connected to the first output terminal (also called “first positive output terminal”) of power module  518 , third positive electrode P3 of LED filament  100  is electrically connected to the second output terminal (also called “second positive output terminal”) of power module  518 , first negative electrode N1 of LED filament  100  is electrically connected to the third output terminal (also called “first negative output terminal”), and second negative electrode N2 is electrically connected to the fourth output terminal (also called “second negative output terminal”) of power module  518 . Under such an arrangement, first positive electrode P1 and second positive electrode P2 can be deemed as the same terminal. Thus, the whole circuit is equivalent to  FIG. 40D . Related control manner, functions and effects can refer to the description of  FIG. 40D . The arrangement of this embodiment can make a single filament have a three-stage dimming effect. 
     Please further refer to  FIG. 41E . In this embodiment, first positive electrode P1 of LED filament  100  is electrically connected to the first output terminal (also called “first positive output terminal”) of power module  518 , second positive electrode P2 of LED filament  100  is electrically connected to the second output terminal (also called “second positive output terminal”) of power module  518 , third positive electrode P3 of LED filament  100  is electrically connected to the third output terminal (also called “third positive output terminal”) of power module  518 , first negative electrode N1 of LED filament  100  is electrically connected to the fourth output terminal (also called “first negative output terminal”), and second negative electrode N2 is electrically connected to the fifth output terminal (also called “second negative output terminal”) of power module  518 . Under such an arrangement, a driving voltage V1 is formed between the first output terminal and the fourth output terminal of power module  518 , another driving voltage V2 is formed between the first output terminal and the fifth output terminal of power module  518 , still another driving voltage V3 is formed between the second output terminal and the fourth output terminal of power module  518 , and yet another driving voltage V4 is formed between the third output terminal and the fifth output terminal of power module  518 . Further refer to  FIG. 41A , under the electrical relationship shown in  FIG. 41E , LED section  402  is electrically connected between the first and fourth terminals, LED section  404  is electrically connected between the first and fifth output terminals, LED section  406  is electrically connected between the second and fourth terminals, and LED section  408  is electrically connected between the third and fifth output terminals. Thus, LED sections  402 ,  404 ,  406 ,  408  can be deemed as being driven by driving voltages V1, V2, V3, V4, respectively. In such an arrangement, the driving currents provided by power module  518  to LED sections  402 ,  404 ,  406 ,  408  can be independently controlled by adjusting output voltages V2, V2, V3, V4 so as to make LED sections  402 ,  404 ,  406 ,  408  separately generate corresponding intensity and/or color temperature. The arrangement of this embodiment can make a single filament have a four-stage dimming effect. 
     In sum, according the abovementioned embodiments, the description has clearly disclosed a strip of filament with multiple dimming control by two, three or four LED sections. According the description, a person having ordinary skill in the art can easily implement a strip of filament with multiple dimming control by five or more LED sections. 
     Next part of the present disclosure will describe the circuit design of the driving circuit of the filament bulb. From circuit perspective, power module  518  in  FIG. 26A  may be represented by a circuit block  5200  (below described and referred to as “power module  5200 ”) as shown in  FIG. 42 .  FIG. 42  is a circuit block diagram of a power module of an LED filament bulb according to some embodiments of present invention. Referring to  FIG. 42 , power module  5200  includes a rectifying circuit  5210 , a filtering circuit  5220 , and a driving circuit  5230 . Rectifying circuit  5210  is coupled to a first pin  5201  and a second pin  5202 , also known as external connection terminals, to receive and then rectify an external driving signal Pin, in order to output a rectified signal Srec through a first rectifying output terminal  5211  and a second rectifying output terminal  5212 . In different embodiments, external driving signal Pin may be an AC driving signal, an AC power supply signal (such as a power grid signal), or even a DC signal, which choices each typically do not affect operations of the LED filament bulb. When the LED filament bulb is designed to emit light or light up based on a DC signal, rectifying circuit  5210  in power module  5200  may be omitted. In a configuration without rectifying circuit  5210 , first rectifying output terminal  5211  and second rectifying output terminal  5212  would be directly coupled to input terminals (as  5211  and  5212 ) of filtering circuit  5220 . 
     Filtering circuit  5220  is coupled to rectifying circuit  5210  in order to filter rectified signal Srec, that is, input terminals of filtering circuit  5220  are coupled to first rectifying output terminal  5211  and second rectifying output terminal  5212  to receive and then filter rectified signal Srec, in order to output a filtered signal Sflr through a first filtering output terminal  5221  and a second filtering output terminal  5222 . First rectifying output terminal  5211  may be regarded as a first filtering input terminal and second rectifying output terminal  5212  may be regarded as a second filtering input terminal, of filtering circuit  5220 . In this embodiment, filtering circuit  5220  may filter out ripples in rectified signal Srec, to make the waveform of produced filtered signal Sflr smoother than that of rectified signal Srec. Besides, circuit configuration of filtering circuit  5220  may be set to realize filtering with respect to a certain or specific (band of) frequency, to filter out frequency response or output energy at a certain or specific frequency in response to external driving signal Pin. 
     Driving circuit  5230  is coupled to filtering circuit  5220 , to receive and then perform power conversion to filtered signal Sflr, in order to generate a driving power Sdrv, that is, input terminals of driving circuit  5230  are coupled to first filtering output terminal  5221  and second filtering output terminal  5222  to receive filtered signal Sflr and then generate driving power Sdrv used for driving LED filament module  100  for emitting light. First filtering output terminal  5221  may be regarded as a first driving input terminal and second filtering output terminal  5222  may be regarded as a second driving input terminal, of driving circuit  5230 . Driving power Sdrv generated by driving circuit  5230  is then provided to LED filament module  100  through a first driving output terminal and a second driving output terminal, to enable an LED filament (as  100 ) of LED filament module  100  to light up in response to driving power Sdrv. Some embodiments of rectifying circuit  5210 , filtering circuit  5220 , and driving circuit  5230  of power module  5200  in possible configurations are presented and described below, but the invention is not limited thereto. 
       FIG. 43A  is a circuit diagram of a rectifying circuit according to some embodiments of present invention. Referring to  FIG. 43A , rectifying circuit  5310  is a bridge rectifier including diodes  5311 - 5314  used for performing (full-wave) rectification to a received signal. Diode  5311  has an anode coupled to a second rectifying output terminal  5212 , and a cathode coupled to a second pin  5202 . Diode  5312  has an anode coupled to second rectifying output terminal  5212 , and a cathode coupled to a first pin  5201 . Diode  5313  has an anode coupled to second pin  5202 , and a cathode coupled to a first rectifying output terminal  5211 . And diode  5314  has an anode coupled to first pin  5201 , and a cathode coupled to first rectifying output terminal  5211 . In this embodiment, diodes  5311 - 5314  may be referred to as first diode  5311 , second diode  5312 , third diode  5313 , and fourth diode  5314 . 
     Operations of rectifying circuit  5310  when first and second pins  5201  and  5202  receive an AC signal as external driving signal Pin are described as follows. During the AC signal&#39;s positive half cycle, assuming the voltage level at first pin  5201  being higher than that at second pin  5202 , diodes  5311  and  5314  operate in a forward-biased state to conduct current, while diodes  5312  and  5313  are cut off as being reverse-biased, which states of the four diodes form a circuit loop between the first and second pins  5201  and  5202 . Under the configuration of the diodes during the AC signal&#39;s positive half cycle, an input current from or caused by the AC signal flows through first pin  5201 , diode  5314 , and first rectifying output terminal  5211  in sequence into a later-stage load, and after which flows through second rectifying output terminal  5212 , diode  5311 , and second pin  5202  in sequence, out of the LED filament bulb. Accordingly, during the AC signal&#39;s negative half cycle, the voltage level at first pin  5202  is higher than that at second pin  5201 , so diodes  5312  and  5313  operate in a forward-biased state to conduct current, while diodes  5311  and  5314  are cut off as being reverse-biased, which states of the four diodes form a circuit loop between first and second pins  5201  and  5202 . Under the configuration of the diodes during the AC signal&#39;s negative half cycle, an input current from or caused by the AC signal flows through second pin  5202 , diode  5313 , and first rectifying output terminal  5211  in sequence into a later-stage load, and after which flows through second rectifying output terminal  5212 , diode  5312 , and first pin  5201  in sequence, out of the LED filament bulb. Therefore, no matter during the AC signal&#39;s positive or negative half cycle, the positive polarity of rectified signal Srec output by rectifying circuit  5310  remains at first rectifying output terminal  5211  and the negative polarity of rectified signal Srec remains at second rectifying output terminal  5212 . According to the above description of operations, the rectified signal output by rectifying circuit  5210  is a full-wave rectified signal. 
     Operations of rectifying circuit  5310  when first and second pins  5201  and  5202  are coupled to a DC power supply to receive a DC signal therefrom as external driving signal Pin are described as follows. When first pin  5201  is coupled to the positive electrode, and second pin  5202  is coupled to the negative electrode, of the DC power supply, diodes  5311  and  5314  operate in a forward-biased state to conduct current, while diodes  5312  and  5313  are cut off as being reverse-biased, which states of the four diodes form a circuit loop between first and second pins  5201  and  5202 . In this case the circuit configuration and operations of rectifying circuit  5310  are the same as those of rectifying circuit  5310  under and during the above-described AC signal&#39;s positive half cycle. On the other hand, when first pin  5201  is coupled to the negative electrode, and second pin  5202  is coupled to the positive electrode, of the DC power supply, diodes  5312  and  5313  operate in a forward-biased state to conduct current, while diodes  5311  and  5314  are cut off as being reverse-biased, which states of the four diodes form a circuit loop between first and second pins  5201  and  5202 . In this case the circuit configuration and operations of rectifying circuit  5310  are the same as those of rectifying circuit  5310  under and during the above-described AC signal&#39;s negative half cycle. 
     From the above description, it is known that no matter whether rectifying circuit  5310  in this embodiment receives an AC signal or a DC signal, rectifying circuit  5310  can properly output rectified signal Srec. 
     Besides, in some embodiments, a capacitor Cx may be disposed between input terminals of rectifying circuit  5310 , wherein capacitance of capacitor Cx may be for example 47 nF and capacitor Cx may be used to reduce EMI (: electromagnetic interference) effects of power module  5200 . 
       FIG. 43B  is a circuit diagram of a rectifying circuit according to some embodiment of present invention. Referring to  FIG. 43B , rectifying circuit  5410  includes diodes  5411  and  5412  used for performing (half-wave) rectification to a received signal. Diode  5411  has an anode coupled to second pin  5202 , and a cathode coupled to first rectifying output terminal  5211 . Diode  5412  has an anode coupled to first rectifying output terminal  5211 , and a cathode coupled to first pin  5201 . Depending on practical applications involving rectifying circuit  5210 , second rectifying output terminal  5212  may be omitted or grounded. In this embodiment, diodes  5411  and  5412  may be referred to as a first diode  5411  and a second diode  5412 . 
     Next, in a similar vein, what follows are descriptions of operations of rectifying circuit  5410  under the two operational situations of when the received signal is an AC signal and when the received signal is a DC signal, respectively. 
     Operations of rectifying circuit  5410  when first and second pins  5201  and  5202  receive an AC signal as external driving signal Pin are described as follows. During the AC signal&#39;s positive half cycle, assuming the input voltage level at first pin  5201  from the AC signal being higher than that at second pin  5202 , diodes  5411  and  5412  are in a reverse-biased state, so rectifying circuit  5410  ceases to output rectified signal Srec, or rectified signal Srec output by rectifying circuit  5410  is at a zero level. On the other hand, during the AC signal&#39;s negative half cycle, the input voltage level at first pin  5201  from the AC signal is lower than that at second pin  5202 , so diodes  5411  and  5412  operate in a forward-biased state to conduct current, causing the AC signal to flow through diode  5411  and first rectifying output terminal  5211  into a later-stage load, after which the current of the AC signal flowing out through second rectifying output terminal  5212 , another circuit of the LED filament bulb, or a ground terminal. According to the above description of operations, the rectified signal output by rectifying circuit  5410  is a half-wave rectified signal. 
     Operations of rectifying circuit  5410  when first and second pins  5201  and  5202  are coupled to a DC power supply to receive a DC signal as external driving signal Pin are described as follows. When first pin  5201  is coupled to the positive electrode, and second pin  5202  is coupled to the negative electrode, of the DC power supply, diodes  5411  and  5412  are cut off as being reverse-biased, so rectifying circuit  5410  ceases to output rectified signal Srec. On the other hand, when first pin  5201  is coupled to the negative electrode, and second pin  5202  is coupled to the positive electrode, of the DC power supply, diodes  5411  and  5412  operate in a forward-biased state to conduct current forming a circuit loop, so in this case the circuit configuration and operations of rectifying circuit  5410  are the same as those of rectifying circuit  5410  under and during the above-described AC signal&#39;s negative half cycle. From this description, in this embodiment, when first pin  5201  is coupled to the negative electrode, and second pin  5202  is coupled to the positive electrode, of the DC power supply, the rectifying circuit  5410  can still operate normally. 
       FIG. 44A  is a circuit diagram of a filtering circuit according to some embodiments of present invention. Referring to  FIG. 44A , the filtering circuit  5320  includes an inductor  5321 , resistors  5322  and  5323 , and capacitors  5324  and  5325 . Inductor  5321  has a first end coupled to first rectifying output terminal  5211 , and has a second end coupled to a first filtering output terminal  5221 . So inductor  5321  is electrically connected between first rectifying output terminal  5211  and first filtering output terminal  5221  in series. Resistor  5322  has a first end coupled to first rectifying output terminal  5211  and the first end of inductor  5321 , and has a second end coupled to first filtering output terminal  5221  and the second end of inductor  5321 . So resistor  5322  and inductor  5321  are electrically connected in parallel. Resistor  5323  has a first end coupled to first filtering output terminal  5221  and the second end of inductor  5321 . Capacitor  5324  has a first end coupled to first filtering output terminal  5221  and the second end of inductor  5321 , and has a second end coupled to second rectifying output terminal  5212  and second filtering output terminal  5222 , wherein second rectifying output terminal  5212  and second filtering output terminal  5222  may be regarded as the same terminal and/or a ground terminal GND. Capacitor  5325  has a first end coupled to a second end of resistor  5323 , and has a second end coupled to second rectifying output terminal  5212  and second filtering output terminal  5222 . Under the structure and configuration of filtering circuit  5320  in this embodiment, filtering circuit  5320  can perform low-pass filtering to rectified signal Srec, to filter out high-frequency components of rectified signal Srec so as to produce a filtered signal Sflr then output through first and second filtering output terminals  5221  and  5222 . 
       FIG. 44B  is a circuit diagram of a filtering circuit according to some embodiments of the present invention. Referring to  FIG. 44B , filtering circuit  5420  comprises a π-shape filtering circuit and includes an inductor  5421 , capacitors  5422 ,  5423 , and  5424 , and resistors  5425  and  5426 . Inductor  5421  has a first end coupled to first rectifying output terminal  5211 , and has a second end coupled to a first filtering output terminal  5221 . So inductor  5421  is electrically connected between first rectifying output terminal  5211  and first filtering output terminal  5221  in series. Capacitor  5422  has a first end coupled to first rectifying output terminal  5211  and first end of inductor  5421 , and has a second end coupled to second rectifying output terminal  5212  and a second filtering output terminal  5222 , so the first end of capacitor  5422  is coupled to first filtering output terminal  5221  through inductor  5421 . Capacitor  5423  has a first end coupled to first filtering output terminal  5221  and the second end of inductor  5421 , and has a second end coupled to second rectifying output terminal  5212  and second filtering output terminal  5222 , so the first end of capacitor  5423  is coupled to first rectifying output terminal  5211  through inductor  5421 . Capacitor  5424  has a first end coupled to first filtering output terminal  5221  and the second end of inductor  5421 , and has a second end coupled to first ends respectively of resistors  5425  and  5426 , whose respective second ends are coupled to second rectifying output terminal  5212  and second filtering output terminal  5222 . 
     By way of structural equivalence, the positional structure of inductor  5421  and capacitor  5423  of filtering circuit  5420  is similar to that of inductor  5321  and capacitor  5324  of filtering circuit  5320 . Compared to filtering circuit  5320  in  FIG. 44A , filtering circuit  5420  further includes capacitor  5422 , which is similar to inductor  5421  and capacitor  5423  in having a low-pass filtering function. So compared to filtering circuit  5320  in  FIG. 44A , filtering circuit  5420  has better ability to filter out high-frequency components, which ability causes the waveform of its output filtered signal Sflr to be smoother. 
     Inductors  5321  and  5421  in the above embodiments each have an inductance preferably in the range of about 10 nH˜10 mH. And capacitors  5324 ,  5325 ,  5422 ,  5423 , and  5424  each have a capacitance preferably in the range of about 100 pF˜1 uF. 
       FIG. 45  is a circuit diagram of a driving circuit according to some embodiments of the present invention. Referring to  FIG. 45 , the driving circuit  5330  includes a switching control circuit  5331  and a conversion circuit  5332 , for performing power conversion based on, or in a mode of being, a current source, in order to drive the LED filament module to emit light. Conversion circuit  5332  includes a switching circuit PSW (which may be referred to as a power switch) and an energy storage circuit ESE. And conversion circuit  5332  is coupled to first and second filtering output terminals  5221  and  5222  to receive and then convert filtered signal Sflr, under the control by switching control circuit  5331 , into a driving power Sdrv to be output at a first and a second driving output terminals  5231  and  5232  for driving the LED filament module. Under the control by switching control circuit  5331 , driving power Sdrv output by conversion circuit  5332  comprises a steady current, causing the LED filament module to steadily emit light. Besides, driving circuit  5330  may further include a biasing circuit  5333 , which may be configured to generate working voltage Vcc based on voltage on an input power line of the power module, wherein working voltage Vcc is provided to and used by switching control circuit  5331 , so that switching control circuit  5331  can be activated and then operate in response to working voltage Vcc. 
     Next, operations of driving circuit  5330  are further described with reference to the illustrating signal waveforms shown in  FIGS. 46A-46D .  FIGS. 46A-46D  are signal waveform diagrams related to and in different embodiments of operating the driving circuit ( 5230 / 5330 ).  FIGS. 46A and 46B  illustrate signal waveforms and control situation in an embodiment of operating driving circuit  5330  in a continuous-conduction mode (CCM).  FIGS. 46C and 46D  illustrate signal waveforms and control situation in an embodiment of operating driving circuit  5330  in a discontinuous-conduction mode (DCM). In the signal-waveform diagrams, the horizontal axis represents time, which is denoted by “t”, and the vertical axis represents the variable of voltage or current depending on which type of signal is being described or referred to. 
     Switching control circuit  5331  in this embodiment is configured to perform real-time regulation or adjusting of the duty cycle of a lighting control signal Slc according to current operational states of the LED filament bulb, in order to turn on or turn off switching circuit PSW according to or in response to lighting control signal Slc. Switching control circuit  5331  can determine or judge a current operational state of the LED filament bulb by detecting one or more of an input voltage (such as a voltage level on first pin  5201  or second pin  5202 , on first rectifying output terminal  5211 , or on first filtering output terminal  5221 ), an output voltage (such as a voltage level on first driving output terminal  5231 ), an input current (such as a current on the input power line or flowing through rectifying output terminal  5211 / 5212  and filtering output terminal  5221 / 5222 ), and an output current (such as a current flowing through driving output terminal  5231 / 5232  or through switching circuit PSW). Energy storage circuit ESE is configured to alternate or switch its operation between being charged with energy and discharging energy, according to the state of switching circuit PSW being turned on or turned off, in order to maintain or make a driving current ILED received by the LED filament module be stably above a predefined current value Ipred. Lighting control signal Slc has a fixed signal period Tlc and a signal amplitude, wherein the pulse on time (such as Ton1, Ton2, or Ton3, and also referred to as a pulse width) during each of signal period Tlc may be adjusted according to control needs. And the duty cycle of lighting control signal Slc is the ratio of the pulse on time to signal period Tlc. For example, if pulse on time Ton1 is 40% of signal period Tlc, this means the duty cycle of lighting control signal Slc during first signal period Tlc is 0.4. 
       FIG. 46A  illustrates variations in signal waveforms during multiple consecutive signal periods Tlc related to operating driving circuit  5330  when driving current ILED is below predefined current value Ipred. Referring to both  FIG. 45  and  FIG. 46A , specifically, during first signal period Tlc, switching circuit PSW conducts current during pulse on time Ton1 when lighting control signal Slc is at a high level. So during pulse on time Ton1, in addition to generating driving current ILED for LED filament module  100  according to input power supply received from first filtering output terminal  5221  and second filtering output terminal  5222 , conversion circuit  5332  electrically charges energy storage circuit ESE through conducting switching circuit PSW so as to gradually increase a current signal IL flowing through energy storage circuit ESE. In other words, during pulse on time Ton1, energy storage circuit ESE is electrically charged to store energy in response to the input power supply received from first filtering output terminal  5221  and second filtering output terminal  5222 . 
     Subsequently, upon the end of pulse on time Ton1, switching circuit PSW is turned off or not conducting in response to lighting control signal Slc being at a low level. During the time that switching circuit PSW is turned off, the input power supply received from first filtering output terminal  5221  and second filtering output terminal  5222  is not provided to the LED filament module, but instead energy storage circuit ESE discharges electrical energy to generate driving current ILED for the LED filament module, wherein current signal IL flowing through energy storage circuit ESE gradually decreases due to the energy discharging. Therefore, even when lighting control signal Slc is at a low level, that is, when switching circuit PSW is turned off or disabled, driving circuit  5330  continues to provide electrical power to the LED filament module due to the energy discharging from and by energy storage circuit ESE. In other words for this case, no matter whether switching circuit PSW is turned on or turned off, driving circuit  5330  will continually provide a stable driving current ILED to the LED filament module, wherein the current value of driving current ILED during first signal period Tlc is about I1 as shown in  FIG. 46A . 
     During first signal period Tlc, switching control circuit  5331  judges that current value I1 of driving current ILED is below a predefined current value Ipred, according to a current detection signal indicative of a working state of the LED filament. Thus upon entering into second signal period Tlc, switching control circuit  5331  adjusts the pulse on time of lighting control signal Slc into Ton2, which is equal to pulse on time Ton1 plus a unit duration t1. 
     During second signal period Tlc, operations of switching circuit PSW and energy storage circuit ESE are similar to their operations during the previous or first signal period Tlc. The difference(s) in operations between two signal periods Tlc is mainly that since pulse on time Ton2 is longer than pulse on time Ton1, the charging time and discharging time of energy storage circuit ESE during second signal period Tlc are longer and shorter respectively than their counterparts during first signal period Tlc, causing an average value I2 of driving current ILED provided by driving circuit  5330  during second signal period Tlc higher than current value I1 and closer to predefined current value Ipred. 
     Similarly, since at this stage current value I2 of driving current ILED is still below predefined current value Ipred, during third signal period Tlc switching control circuit  5331  again adjusts the pulse on time of lighting control signal Slc into Ton3, which is equal to pulse on time Ton2 plus unit duration t1 or equal to pulse on time Ton1 plus duration t2 of 2 unit durations t1. During third signal period Tlc, operations of switching circuit PSW and energy storage circuit ESE are similar to their operations during each of first two signal periods Tlc. Because pulse on time Ton3 is further longer than pulse on time Ton2, the current value of driving current ILED provided by driving circuit  5330  during third signal period Tlc is raised to I3 approximately reaching predefined current value Ipred. Afterwards, since current value I3 of driving current ILED during third signal period Tlc has reached predefined current value Ipred, switching control circuit  5331  maintains a constant duty cycle of lighting control signal Slc, to maintain the current value of driving current ILED continually at predefined current value Ipred. 
       FIG. 46B  illustrates variations in signal waveforms during multiple consecutive signal periods Tlc related to operating driving circuit  5330  when driving current ILED is above predefined current value Ipred. Referring to both  FIG. 45  and  FIG. 46B , specifically, during first signal periods Tlc shown in  FIG. 46B , switching circuit PSW conducts current during pulse on time Ton1 when lighting control signal Slc is at a high level. So during pulse on time Ton1, in addition to generating driving current ILED for LED filament module  18  according to input power supply received from first filtering output terminal  5221  and second filtering output terminal  5222 , conversion circuit  5332  electrically charges energy storage circuit ESE through conducting switching circuit PSW so as to gradually increase a current signal IL flowing through energy storage circuit ESE. In other words, during pulse on time Ton1, energy storage circuit ESE is electrically charged to store energy in response to the input power supply received from first filtering output terminal  5221  and second filtering output terminal  5222 . 
     Subsequently, upon the end of pulse on time Ton1, switching circuit PSW is turned off or not conducting in response to lighting control signal Slc being at a low level. During the time that switching circuit PSW is turned off, the input power supply received from first filtering output terminal  5221  and second filtering output terminal  5222  is not provided to LED filament module  100 , but instead energy storage circuit ESE discharges electrical energy to generate driving current ILED for LED filament module  100 , wherein current signal IL flowing through energy storage circuit ESE gradually decreases due to the energy discharging. Therefore, even when lighting control signal Slc is at a low level, that is, when switching circuit PSW is turned off or disabled, driving circuit  5330  continues to provide electrical power to LED filament module  100  due to the energy discharging from and by energy storage circuit ESE. In other words for this case, no matter whether switching circuit PSW is turned on or turned off, driving circuit  5330  will continually provide a stable driving current ILED to LED filament module  100 , wherein the current value of driving current ILED during first signal period Tlc is about I4 as shown in  FIG. 46B . 
     During first signal period Tlc, switching control circuit  5331  judges that current value I4 of driving current ILED is above a predefined current value Ipred, according to a current detection signal Sdet. Thus upon entering into second signal period Tlc, switching control circuit  5331  adjusts the pulse on time of lighting control signal Slc into Ton2, which is equal to pulse on time Ton1 minus a unit duration t1. 
     During second signal period Tlc, operations of switching circuit PSW and energy storage circuit ESE are similar to their operations during previous or first signal period Tlc. The difference(s) in operations between two signal periods Tlc is mainly that since pulse on time Ton2 is shorter than pulse on time Ton1, the charging time and discharging time of energy storage circuit ESE during second signal period Tlc are shorter and longer respectively than their counterparts during first signal period Tlc, causing an average value I5 of driving current ILED provided by driving circuit  5330  during second signal period Tlc lower than current value I4 and closer to predefined current value Ipred. 
     Similarly, since at this stage current value I5 of driving current ILED is still above predefined current value Ipred, during third signal period Tlc switching control circuit  5331  again adjusts the pulse on time of lighting control signal Slc into Ton3, which is equal to pulse on time Ton2 minus unit duration t1 or equal to pulse on time Ton1 minus duration t2 of 2 unit durations t1. During third signal period Tlc, operations of switching circuit PSW and energy storage circuit ESE are similar to their operations during each of first two signal periods Tlc. Because pulse on time Ton3 is further shorter than pulse on time Ton2, the value of driving current ILED provided by driving circuit  5330  during third signal period Tlc is lowered to I6 approximately reaching predefined current value Ipred. Afterwards, since current value I6 of driving current ILED during third signal period Tlc has reached predefined current value Ipred, switching control circuit  5331  maintains a constant duty cycle of lighting control signal Slc, to maintain the current value of driving current ILED continually at predefined current value Ipred. 
     From the above descriptions of the embodiments of both  FIGS. 46A and 46B , it&#39;s seen that driving circuit  5330  adjusts the pulse width or pulse on time of lighting control signal Slc for each of consecutive signal periods Tlc, in a stepping manner depending on the level of driving current ILED in relation to predefined current value Ipred, to gradually bring the value of driving current ILED above or below predefined current value Ipred to approach or be closer to predefined current value Ipred, so as to realize outputting of a stable or constant current. 
     In addition, the above embodiments of  FIGS. 46A and 46B  are examples of operating driving circuit  5330  in a continuous-conduction mode, wherein when switching circuit PSW is turned off energy storage circuit ESE does not discharge current to the extent that current signal IL flowing through energy storage circuit ESE decreases to zero. By using driving circuit  5330  operating in the continuous-conduction mode to provide power for the LED filament module, the electrical power provided to the LED filament module is relatively stable and is not likely to cause signal ripples. 
     Next are descriptions of embodiments of a control situation of operating driving circuit  5330  in a discontinuous-conduction mode. Referring to both  FIG. 45  and  FIG. 46C , the signal waveforms and operations of the driving circuit  5330  shown by  FIG. 46C  are similar to those shown by  FIG. 46A . The difference(s) between the two embodiments of  FIG. 46C  and  FIG. 46A  is mainly that because driving circuit  5330  in this embodiment of  FIG. 46C  operates in a discontinuous-conduction mode, when switching circuit PSW is turned off or disabled by lighting control signal Slc being at a low level energy storage circuit ESE discharges current to the extent that current signal IL flowing through energy storage circuit ESE decreases to zero, followed by energy storage circuit ESE being charged again upon starting of next signal period Tlc. Apart from this difference, description of other operations of this embodiment of  FIG. 46C  can be referred to the above description of the embodiment of  FIG. 46A  and so is not repeated again. 
     Then referring to both  FIG. 45  and  FIG. 46D , the signal waveforms and operations of driving circuit  5330  shown by  FIG. 46D  are similar to those shown by  FIG. 46B . The difference(s) between the two embodiments of  FIG. 46D  and  FIG. 46B  is mainly that because driving circuit  5330  in this embodiment of  FIG. 46D  operates in a discontinuous-conduction mode, when switching circuit PSW is turned off or disabled by lighting control signal Slc being at a low level energy storage circuit ESE discharges current to the extent that current signal IL flowing through energy storage circuit ESE decreases to zero, followed by energy storage circuit ESE being charged again upon starting of next signal period Tlc. Apart from this difference, description of other operations of this embodiment of  FIG. 46D  can be referred to the above description of the embodiment of  FIG. 46B  and so is not repeated again. 
     By using driving circuit  5330  operating in the discontinuous-conduction mode to provide power for the LED filament module, energy or power loss incurred in performing power conversion by driving circuit  5330  can be reduced, thereby resulting in a higher conversion efficiency. The following are descriptions to introduce and further explain several concrete circuit examples of driving circuit  5330 . 
       FIG. 47A  is a circuit diagram of a driving circuit according to some embodiments of the present invention. Referring to  FIG. 47A , in this embodiment, driving circuit  5430  comprises a buck DC-to-DC converter circuit, including a controller  5431 , an output circuit  5432 , a biasing circuit  5433  and a sampling circuit  5434 . Driving circuit  5430  is coupled to first filtering output terminal  5221  and second filtering output terminal  5222  to convert received filtered signal Sflr to driving power Sdrv for driving the LED filament module coupled between first and second driving output terminals  5231  and  5232 . 
     Controller  5431  includes for example an integrated-circuit chip, which has a drain-terminal or drain pin Pdrn, a source-terminal or source pin Pcs, an power pin Pvcc, a voltage sampling pin Pln, an overvoltage protection pin Povp, and a ground pin Pgnd. Drain pin Pdrn is coupled to output circuit  5432 . Source pin Pcs is coupled to second filtering output terminal  5222  and ground terminal GND through a resistor Rs. Power pin Pvcc and overvoltage protection pin Povp are coupled to biasing circuit  5433 . Voltage sampling pin Pln is coupled to sampling circuit  5434 . And ground pin Pgnd is coupled to second filtering output terminal  5222  and ground terminal GND. 
     In this embodiment of  FIG. 47A , the above-mentioned switching circuit or power switch (PSW) of conversion circuit  5332  is for example integrated in controller  5431 , and has first and second terminals electrically connected to drain pin Pdrn and source pin Pcs respectively. Therefore, controller  5431  can determine current conduction or cutoff at or through drain pin Pdrn, source pin Pcs, and/or corresponding current path(s), by controlling switching of its internal switching circuit between, or into one of, conduction and cutoff states. In some other embodiments, the above-mentioned switching circuit is a discrete device disposed external to controller  5431 . In applications using a discrete device as switching circuit, definitions or connection-structure of pins of controller  5431  would be adjusted accordingly, such as setting drain pin Pdrn as a pin to be electrically connected to a control terminal of the discrete switching circuit instead and for providing a lighting control signal. 
     Output circuit  5432  includes a diode D1, an inductor L1, a capacitor Co, and a resistor Ro, wherein inductor L1 and capacitor Co act as (part of) the energy storage circuit (ESE) of conversion circuit  5332 . Diode D1 acts as a freewheeling diode; has its anode coupled to drain pin Pdrn of controller  5431  so as to be coupled through drain pin Pdrn to the first or drain terminal of the switching circuit (PSW) within controller  5431 ; and has its cathode coupled to first driving output terminal  5231  Inductor L1 has a first end coupled to the anode of the diode D1 and the drain pin Pdrn of the controller  5431 , and has a second end coupled to first filtering output terminal  5221  and second driving output terminal  5232 . Resistor Ro and capacitor Co are electrically connected in parallel and coupled between first and second driving output terminals  5231  and  5232 . In this embodiment, first filtering output terminal  5221  and second driving output terminal  5232  can be regarded as the same terminal. 
     In this embodiment of  FIG. 47A , the controller  5431  is configured to control current conduction or cutoff on a path between drain pin Pdrn and source pin Pcs. When there is current conduction on the path between drain pin Pdrn and source pin Pcs, a current flows from first filtering output terminal  5221  into driving circuit  5430 , and flows through inductor L1 and drain pin Pdrn into controller  5431 , and then flows through source pin Pc and second filtering output terminal  5222  to ground terminal GND. In this case of current conduction, the current flowing through inductor L1 increases with time and causes inductor L1 to be in a state of storing electrical energy; while the voltage across capacitor Co decreases with time and causes capacitor Co to be in a state of releasing electrical energy in order to maintain the LED filament module as emitting light. On the other hand, when the path between drain pin Pdrn and source pin Pcs is in a cutoff state or not conducting current, inductor L1 is in a state of releasing or discharging electrical energy and the current flowing through inductor L1 decreases with time. In this cutoff case the current flowing through inductor L1 flows through diode D1, first driving output terminal  5231 , the LED filament module, second driving output terminals  5232 , and then back to inductor L1, forming a current flyback; and capacitor Co is in a state of storing electrical energy with its voltage increasing with time. 
     It should be noted that capacitor Co may be omitted. When capacitor Co is omitted, and there is current conduction on the path between drain pin Pdrn and source pin Pcs, a current flowing through inductor L1 doesn&#39;t flow through first filtering output terminal  5221  and second driving output terminal  5232 , so the LED filament module does not emit light. But when the path between drain pin Pdrn and source pin Pcs is in a cutoff state, a current flowing through inductor L1 flows through freewheeling diode D1 to the LED filament module to cause the LED filament to emit light. By adjusting or controlling the duration of light emission by the LED filament and the magnitude of current flowing through the LED filament module, an average luminance of the emitted light stable above a defined value can be achieved, so as to achieve a favorable function of emitting stable light. Apart from the above, since driving circuit  5430  of this embodiment takes a non-isolation power-conversion structure, feedback control, if any, of switching circuit or power switch (PSW) performed by controller  5431  may be based on detecting a magnitude of current flowing through the switching circuit or power switch. 
     In another aspect, driving circuit  5430  keeps the current flowing through the LED module unvariable, so for some LED modules (for example, white, red, blue and green LED modules), it can be improved that color temperature changes with current. In other words, the LED module can keep color temperature constant under different current intensity. Inductor L1 which serves as an energy storage circuit releases stored energy when the switching circuit turns off. This makes not only the LED filament keep lighting but also the current in the LED filament does not suddenly drop to the lowest value. When the switching circuit turns on again, it is unnecessary that both current and voltage goes from the lowest value to the highest value. Thereby, discontinuous lighting of LED filament can be avoided to cause the luminance of the LED filament being varied, to decrease the lowest conducting cycle and to raise the driving frequency. 
     Biasing circuit  5433  includes capacitor C1 and resistors R1-R4. A first end of capacitor C1 is electrically connected to power pin Pvcc. A second end of capacitor C1 is electrically connected to second filtering output terminal  5222  and ground terminal GND. A first end of resistor R1 is electrically connected second driving output terminal  5232 . A first end of resistor R2 is electrically connected to a second end of resistor R1. A second end of resistor R2 is electrically connected to the first end of capacitor C1 and power pin Pvcc. A first end of resistor R3 is electrically connected a second end of resistor R1 and the first end of resistor R2. A second end of resistor R3 is electrically connected to overvoltage protection pin Povp of controller  5431 . A first end of resistor R4 is electrically connected to the second end of resistor R3. A second end of resistor R4 is electrically connected to both second filtering output terminal  5222  and ground terminal GND. 
     Resistors R1 and R2 acquire a voltage of second driving output terminal  5232  to generate working voltage Vcc. Working voltage Vcc is stabilized by capacitor C1 and transmitted to power pin Pvcc for being used by controller  5431 . Resistors R3 and R4 acquire or sample a voltage of second driving output terminal  232  by voltage division so that controller  5431  can determine if the overvoltage protection function should be executed or not according to the voltage of overvoltage protection pin Povp. 
     Sampling circuit  5434  includes capacitor C2 and resistors R5-R7. A first end of capacitor C2 is electrically connected to voltage sampling pin Pln. A second end of capacitor C2 is electrically connected to both second filtering output terminal  5222  and ground terminal GND. A first end of resistor R5 is electrically connected to both first filtering output terminal  5221  and second driving output terminal  5232 . A first end of resistor R6 is electrically connected to a second end of resistor R5. A second end of resistor R6 is electrically connected to both second filtering output terminal  5222  and ground terminal GND. A first end of resistor R7 is electrically connected to both the second end of resistor R7 and the first end of resistor R6. A second end of resistor R7 is electrically connected to both voltage sampling pin Pln and the first end of capacitor C2. 
     Resistors R5 and R6 acquire or sample a voltage of the power line (i.e. the voltage of first filtering output terminal  5221 ) by voltage division. The sampled voltage is transmitted to voltage sampling pin Pln of controller  5431  through resistor R7. Capacitor C2 is used for stabilizing a voltage of voltage sampling pin Pin. 
     Please refer to  FIG. 47B , which is a schematic circuit diagram of the driving circuit according to some embodiments of the present invention. In this embodiment, a boost DC-to-DC converter serves as the driving circuit  5530  as an example, which includes controller  5531 , output circuit  5532 , biasing circuit  5533  and sampling circuit  5534 . The driving circuit is electrically connected to both first filtering output terminal  5221  and second filtering terminal  5222  for converting the received filtered signal Sflr into a driving power Sdrv to drive the LED filament module electrically connected between first and second driving output terminals  5231  and  5232 . In addition, driving circuit  5530  is further electrically connected to first rectifying output terminal  5211  for acquiring voltage of the power line (or bus line) to generate working voltage Vcc. 
     Controller  5531  may be an integrated circuit or a chip including drain pin Pdrn, source pin Pcs, power pin Pvcc, overvoltage protection pin Povp and ground pin Pgnd. Drain pin Pdrn is electrically connected to output circuit  5532 . Source pin Pcs is electrically connected to second filtering output terminal  5222 , second driving output terminal  5532  and ground terminal GND through capacitor Cs. Power pin Pvcc is electrically connected to biasing circuit  5533 . Overvoltage protection pin Povp is electrically connected to sampling circuit  5534 . Ground pin Pgnd is electrically connected to both biasing circuit  5533  and sampling circuit  5534 . 
     In this embodiment, the switching circuit/power switch (PSW) may be integrated in controller  5531 , and the first end and the second end of the switching circuit are electrically connected to drain pin Pdrn and source pin Pcs, respectively. In other words, controller  5531  can determine switch-on or switch-off of a current path related to drain pin Pdrn and source pin Pcs by controlling the switching state of the switching circuit within controller  5531 . In another embodiments, the switching circuit may also be a discrete element which is not integrated into controller  5531 . Under such a situation using a discrete element as a switching circuit, definition of pinout of controller  5531  will be correspondingly adjusted. For example, drain pin Pdrn can be adjusted to connect to a control end of the switching circuit and to serve as a pin providing a lighting control signal. 
     Output circuit  5532  includes diode D1, inductor L1, capacitor Co and resistor Ro. Both inductor L1 and capacitor C1 serve as an energy storage circuit (ESE) of the converting circuit. Diode D1 serves as a freewheeling diode, whose anode is electrically connected to drain pin Pdrn of controller  5531  by connecting drain pin Pdrn to the first end/drain of the switching circuit in controller  5531 . The cathode of diode D1 is electrically connected to first driving output terminal  5231 . The first end of inductor L1 is electrically connected to first filtering output terminal  5221 . The second end of inductor L1 is electrically connected to both drain pin Pdrn of controller  431  and the anode of diode D1. Resistor Ro and capacitor Co are electrically connected in parallel and electrically connected between first driving output terminal  5231  and second driving output terminal  5232 . In this embodiment, first filtering output terminal  5221  is electrically connected to first driving output terminal  5231  via both diode D1 and inductor L1. 
     Controller  5531  controls switch-on and switch-off between drain pin Pdrn and source pin Pcs. When circuit between drain pin Pdrn and source pin Pcs is switched on, current will flow in first filtering output terminal  5521  to controller  5531  via inductor L1 and drain pin Pdrn, and finally flow to ground terminal GND via source pin Pcs, capacitor Cs and second filtering output terminal  5222 . At this time, current flowing through inductor L1 increases with time and inductor L1 is in a status of energy storing. Meanwhile, capacitor Co is in a status of energy releasing to drive the LED filament module to emit light. When drain pin Pdrn and source pin Pcs are switched off, inductor L1 is in a status of energy releasing, and the current in inductor L1 decreases with time. The current in inductor L1 flows to capacitor Co and the LED filament via diode D1. At this time, capacitor Co is in a status of energy storing. 
     It is noted that capacitor Co may be omitted. When capacitor Co is omitted and drain pin Pdrn and source pin Pcs are switched on, the current in inductor L1 does not flow through first driving output terminal  5231  and second driving output terminal  5232  to make the LED filament module not light. When drain pin Pdrn and source pin Pcs are switched off, the current in inductor L1 flows to the LED filament module via freewheeling diode D1 to light up the LED filament. By controlling lighting time of the LED filament and magnitude of the current flowing therethrough, the average intensity of the LED filament can be stabilized at a predetermined value to obtain an effect of identically stable lighting. 
     Biasing circuit  5533  includes diode D2, capacitor C1 and resistor R1. The anode and the cathode of diode D1 are electrically connected to first rectifying output terminal  5211  and first driving output terminal  5231 , respectively. The first end and the second end of capacitor C1 are electrically connected to power pin Pvcc and ground pin Pgnd, respectively. The first end of resistor R1 is electrically connected to cathodes of diodes D1 and D2 and first driving output terminal  5231 . The second end of resistor R1 is electrically connected to the first end of capacitor C1 and power pin Pvcc. Resistor R1 acquires a voltage of first driving output terminal  5231  to generate a working voltage Vcc. Working voltage Vcc is stabilized by capacitor C1 and transmitted to power pin Pvcc of controller  5431  for being used by controller  5431 . 
     Sampling circuit  5534  includes resistor R2-R5. The first end and the second end of resistor R2 are electrically connected to first driving output terminal  5231  and overvoltage protection pin Povp, respectively. Resistors R3 and R4 are electrically connected in parallel. The first ends of resistors R3 and R4 are electrically connected to ground pin Pgnd. The second ends of resistors R3 and R4 are electrically connected to second filtering output terminal  5222 , second driving output terminal  5232  and ground terminal GND. The first end and the second end of resistor R5 are electrically connected to ground pin Pgnd and both the second end of resistor R2 and overvoltage protection terminal Povp. 
     Resistors R2 to R5 acquire or sample a voltage of the output voltage (i.e. the voltage of first driving output terminal  5231 ) by voltage division. The sampled voltage is transmitted to overvoltage protection pin Povp of controller  5531 . As a result, controller  5531  can determine if the overvoltage protection function should be executed or not according to a voltage of overvoltage protection pin Povp. 
     Additionally, driving circuits  5430 ,  5530  is shown by a single-stage DC-to-DC power conversion circuit as an example, but not limited to this. For example, driving circuit  5330  can be a two-stage power conversion circuit which includes an active power factor correction circuit and a DC-to-DC converter. 
     The various embodiments of the present invention described above may be arbitrarily combined and transformed without being mutually exclusive, and are not limited to a specific embodiment. For example, some features as described in the embodiment shown in FIG. C although not described in the embodiment shown in FIG. A, those features may be included in the embodiment of FIG. A. That is, those skilled in the art can applies some features of the FIG. A to the embodiment shown in the FIG. C without additional creativity. Or alternatively, although the invention has illustrated various creation schemes by taking the LED light bulb as an example, it is obvious that these designs can be applied to other shapes or types of light bulb without additional creativity, such as LED candle bulbs, and the like. 
     The LED filament of the present invention and the LED light bulb of the application thereof have been implemented as described above, and it should be reminded that for the same LED filament or the LED light bulb using the LED filament, the features pertaining to aforementioned embodiments such as “light conversion layer”, “light conversion layer wrapping conductive electrode and/or LED chip”, “wire”, “silicon gel and/or polyimide and/or resin”, “phosphor particles constitute a ratio”, “filament layer structure”, “phosphor glue/film conversion wavelength/particle size/thickness/transmittance/hardness/shape”, “transparent layer”, “phosphor particles constitute a heat conduction path”, “circuit film”, “oxidation nanoparticles (inorganic heat dissipating particles), “die bond paste”, “LED filament body wavy”, “stem”, “gas in lamp housing”, “filament assembly”, “the length of conductive brackets”, “the length of the conductive brackets of the LED filament”, “the surface of the supporting arm and/or stem can be coated with a graphene film”, “the pressure inside the lamp housing”, “the Young&#39;s modulus of the LED filament”, “Shore scleroscope hardness of the LED filament base layer”, “auxiliary strip”, “lamp housing surface coating adhesive film, diffusion film, color film”, “lamp housing/stem/pole with light conversion substance”, “lamp housing having thermal dissipation area”, “filament hole or notch”, “thermal dissipation path in the LED filament”, “curve formula of filament shape”, “ventilation hole of lamp housing”, “wavy fitting interface between the top layer and the base layer of the LED filament”, the fitting surface is serrated”, “through hole of the base layer”, “light conversion layer includes the first fluorescent adhesive layer, the second fluorescent adhesive layer and the transparent layer”, “auxiliary strip in wavy shape”, “auxiliary strip in spiral shape”, “multiple auxiliary strips are arranged in both horizontal and vertical”, “at least one end of the longitudinal auxiliary strip is bent into an L shape”, “the LED filament having bends”, “no pole in lamp housing”, “lamp housing with spray coating”, “lamp housing raw materials with doped color”, “butt seal between lamp housing and stem”, “the wall thickness of the lamp housing is different from that of the stem “,” the wall thickness of the lamp housing is thicker than that of the stem“,” holes or gaps are appropriately set near the bending portion”, “the width of the LED chip is smaller than the width of the base layer or the top layer”, “the shape and/or the thickness of the top layer, and even the center of the top layer whether overlaps with the light emitting surface of the LED chip were the factors in the light emitting efficiency” may be included, whatever one, two, more, or all technical features under non-conflicting situations. The LED filament related components and the connection thereof may be selected from one or a combination of the technical features included in the corresponding embodiments. 
     The invention has been described above in terms of the embodiments, and it should be understood by those skilled in the art that the present invention is not intended to limit the scope of the invention. It should be noted that variations and permutations equivalent to those of the embodiments are intended to be within the scope of the present invention. Therefore, the scope of the invention is defined by the scope of the appended claims.