Patent Publication Number: US-10767817-B2

Title: LED light bulb and LED filament thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 16/259,982 filed on 2019 Jan. 28, which is a continuation application of U.S. patent application Ser. No. 15/237,983 filed on 2016 Aug. 16, which claims priority to Chinese Patent Applications No: 201510502630.3 filed on 2015 Aug. 17; No. 201510966906.3 filed on 2015 Dec. 19; No. 201610041667.5 filed on 2016 Jan. 22; No. 201610272153.0 filed on 2016 Apr. 27; No. 201610281600.9 filed on 2016 Apr. 29; No. 201610394610.3 field on 2016 Jun. 3 and No. 201610586388.7 filed on 2016 Jul. 22, each of which is hereby incorporated by reference in its entirety. 
     This application claims priority to Chinese Patent Applications No: 201510502630.3 filed on 2015 Aug. 17; No. 201510966906.3 filed on 2015 Dec. 19; No. 201610041667.5 filed on 2016 Jan. 22; No. 201610272153.0 filed on 2016 Apr. 27; No. 201610281600.9 filed on 2016 Apr. 29; No. 201610394610.3 field on 2016 Jun. 3 and No. 201610586388.7 filed on 2016 Sep. 22, each of which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The instant disclosure relates to illumination field, and more particularly, to an LED light bulb and an LED filament thereof. 
     RELATED ART 
     The LED has advantages of environmental protection, energy saving, high efficiency and long lifespan, and therefore it attracts widespread attention in recent years and gradually replaces traditional lighting lamps. However, due that the luminescence of the LED has directivity, current LED lamps is unable to provide with an illumination with a wide angle range like traditional lamps. Accordingly, how to design LED lamps with similar wide range for illumination to the traditional lamps challenges the industries. 
     In order to provide with an illumination with a wide range, optical components like lenses, prisms, reflectors are utilized to adjust light distribution emitted originally from the LED. However, the optical components for adjusting the light distribution decrease the overall optical efficiency of LED lamps. Consequently, how to improve the optical efficiency and provide with wide range for illumination are important tasks in the lighting industry. 
     Next, an LED die without package can be deemed as a full-angle light source and is capable of providing with full-range illumination. However, the package of LED narrows the illumination angle and decreases optical efficiency. 
     Further, a lamp with a LED filament is more possible to provide wide-range illumination and its outlook is closer to that of the traditional incandescent (tungsten) light bulbs. This is also one of advantages of light bulb with a LED filament. 
     One of the challenges of LED light bulbs is omnidirectional lighting. Current LED light bulbs utilize LED filaments. The LED filament has LED chips on a strip substrate and mixtures of silica gel with phosphor coated on the LED chips. The substrate is usually a glass substrate or a metal substrate. The glass substrate has the advantages of not blocking light emitted from LED chips; however, its disadvantages include that the thermal conductivity of the glass substrate is not good and the glass substrate is fragile. Likewise, the LED chips are disposed on the metal substrate having excellent thermal conductivity, but light emitted from the LED chips will be blocked from the metal substrate side. Additionally, the substrates of conventional LED filaments are hard and not bendable. Accordingly, in order to provide with omnidirectional lighting, the conventional LED light bulb utilizes a number of LED filaments symmetrically positioned inside a bulb shell. The utilization of multiple LED filaments increases the cost of the LED bulb because of its complicated manufacturing processes, complex assembly procedures and low yield rate. Additionally, the more LED filaments in a light bulb, the more soldering spots between filaments and filament supports there are as well as the higher possibility soldering defects happens. 
     US patent publication number 20130058080A1 discloses an LED light bulb and an LED light-emitting strip capable of emitting 4π light. The LED light bulb comprises an LED light bulb shell, a core column with an exhaust tube and a bracket, at least one LED light emitting strip with LED chips therein emitting 4π light, a driver, and an electrical connector. The LED light bulb shell is vacuum sealed with the core column so as to form a vacuum sealed chamber. The vacuum sealed chamber is filled with a gas having a low coefficient of viscosity and a high coefficient of thermal conductivity. The bracket and the LED light emitting strips fixed on the bracket are housed in the vacuum sealed chamber. The LED light emitting strip is in turn electrically connected to the driver, the electrical connector, while the electrical connector is used to be electrically connected to an external power supply, so as to light the LED light emitting strips. 
     SUMMARY 
     To address the issues, the instant disclosure provides with embodiments of an LED filament, a manufacturing method therefore, and an LED light bulb utilizing the LED filament. 
     According to an embodiment, an LED filament comprising a plurality of LED chips, at least two conductive electrodes disposed corresponding to the plurality of LED chips, and a light conversion coating. The plurality of LED chips and the conductive electrodes are electrically connected therebetween. The light conversion coating comprises an adhesive and a plurality of phosphors. The light conversion coating coats on at least two sides of the LED chips and the conductive electrodes. The light conversion coating exposes a portion of two of the conductive electrodes. The phosphors in the light conversion coating are capable of emitting light after absorbing some form of radiation. 
     According to an embodiment, the LED filament further comprises a plurality of conductive wires electrically and correspondingly connected among the plurality of LED chips and the conductive electrodes. The light conversion coating covers the plurality of conductive wires. 
     According to an embodiment, the LED filament further comprises a plurality of circuit films electrically and correspondingly connected among the plurality of LED chips and the conductive electrodes. The light conversion coating covers the plurality of the circuit films. 
     According to an embodiment, each of the circuit films comprises a first film and a conductive circuit disposed thereon. The conductive circuits are electrically and correspondingly connected among the plurality of LED chips and the conductive electrodes. 
     According to an embodiment, the light conversion coating comprises a base layer and a top layer. The plurality of LED chips is on a side of the base layer. The Shore D Hardness of the base layer is at least 60 HD. 
     According to an embodiment, the light conversion coating further comprises oxidized nanoparticles. The size of the oxidized nanoparticles is substantially smaller than the size of the phosphors. 
     According to an embodiment, the Young&#39;s Modulus of the LED filament is between 0.1×10 10  Pa to 0.3×10 10  Pa. The composition ratio of the plurality of the phosphors to the adhesive is between 1:1 and 99:1. 
     According to an embodiment, an LED light bulb comprises a bulb shell, a bulb base connected with the bulb shell, at least two conductive supports disposed in the bulb shell, and a single LED filament disposed in the light bulb. The LED filament comprises a plurality of LED chips, at least two conductive electrodes disposed corresponding to the plurality of LED chips, and a light conversion coating. The plurality of LED chips and the conductive electrodes are electrically connected therebetween. The conductive electrodes are electrically and respectively connected with the conductive supports. The light conversion coating coats on at least two sides of the LED chips and the conductive electrodes. The light conversion coating exposes a portion of two of the conductive electrodes. The light conversion coating comprises an adhesive and a plurality of phosphors. 
     According to an embodiment, the LED light bulb further comprises a stem in the bulb shell and a heat dissipating element between the bulb shell and bulb base. The heat dissipating element is connected with the stem. The LED filament connected with the stem. 
     According to some embodiments, each of the surfaces of the LED chips is covered by the light conversion coating. The phosphors of light conversion coating may absorb light out of the surfaces of the LED chips and emit light with longer wavelength. Since the LED chips are surrounded by the light conversion coating to form the main body of the LED filament, the LED filament is capable of emitting light from the sides of the filament having the light conversion coating, and being bended with adequate rigidity. The LED light bulb is capable of emitting omnidirectional light with the single LED filament. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a perspective view of an LED light bulb with partial sectional view according to a first embodiment of the LED filament; 
         FIG. 2  illustrates a partial cross-sectional view at section  2 - 2  of  FIG. 1 ; 
         FIGS. 3A and 3B  illustrate disposition of the metal electrodes and the plurality of LED chips according to other embodiments of the LED filament; 
         FIG. 4  illustrates a perspective view of an LED filament with partial sectional view according to a second embodiment of the present disclosure; 
         FIG. 5  illustrates a partial cross-sectional view at section  5 - 5  of  FIG. 4 ; 
         FIG. 6A  illustrates a first embodiment of the uncut circuit film according to the second embodiment of the LED filament; 
         FIG. 6B  illustrates the alignment between the LED chips and the first embodiment of the uncut circuit film of  FIG. 6A ; 
         FIG. 7A  illustrates a second embodiment of the uncut circuit film according to the second embodiment of the LED filament; 
         FIG. 7B  illustrates the alignment between the LED chips and the second embodiment of the uncut circuit film of  FIG. 7A ; 
         FIG. 8A  illustrates a third embodiment of the uncut circuit film according to the second embodiment of the LED filament; 
         FIG. 8B  illustrates the alignment between the LED chips and the third embodiment of the uncut circuit film of  FIG. 8A ; 
         FIGS. 9A to 9E  illustrate a manufacturing method of an LED filament according to a first embodiment of the present disclosure; 
         FIG. 10  illustrates a manufacturing method of an LED filament according to a second embodiment of the present disclosure; 
         FIGS. 11A to 11E  illustrate a manufacturing method of an LED filament according to a third embodiment of the present disclosure; 
         FIGS. 12A and 12B  illustrate a perspective view of an LED light bulb according to a first and a second embodiments of the present disclosure; 
         FIG. 13A  illustrates a perspective view of an LED light bulb according to a third embodiment of the present disclosure; 
         FIG. 13B  illustrates an enlarged cross-sectional view of the dashed-line circle of  FIG. 13A ; 
         FIG. 14A  illustrates a cross-sectional view of an LED light bulb according to a fourth embodiment of the present disclosure; and 
         FIG. 14B  illustrates the circuit board of the driving circuit of the LED light bulb according to the fourth embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The instant disclosure provides an LED filament and an LED light bulb to solve the abovementioned problems. The instant disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the disclosure are shown. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like reference numerals 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 disclosure. 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. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” or “has” and/or “having” when used herein, 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 the term “and/or” includes any and all combinations of one or more of the associated listed items. It will also be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, parts and/or sections, these elements, components, regions, parts and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, part or section from another element, component, region, layer or section. Thus, a first element, component, region, part or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present disclosure. 
     The following description with reference to the accompanying drawings is provided to explain the exemplary embodiments of the disclosure. Note that in the case of no conflict, the embodiments of the present disclosure and the features of the embodiments may be arbitrarily combined with each other. 
     As indicated in the section of the cross-reference, the instant disclosure claims priority of several Chinese patent applications, and the disclosures of which are incorporated herein in their entirety by reference. When it comes to claim construction, the claims, specification, and prosecution history of the instant disclosure controls if any inconsistency between the instant disclosure and the incorporated disclosures exists. 
     Please refer to  FIGS. 1 and 2 .  FIG. 1  illustrates a perspective view of an LED filament with partial sectional view according to a first embodiment of the present disclosure while  FIG. 2  illustrates a partial cross-sectional view at section  2 - 2  of  FIG. 1 . According to the first embodiment, the LED filament  100  comprises a plurality of LED chips  102 ,  104 , at least two conductive electrodes  110 ,  112 , and a light conversion coating  120 . The conductive electrodes  110 ,  112  are disposed corresponding to the plurality of LED chips  102 ,  104 . The LED chips  102 ,  104  are electrically connected together. The conductive electrodes  112 ,  114  are electrically connected with the plurality of LED chips  102 ,  104 . The light conversion coating  120  coats on at least two sides of the LED chips  102 ,  104  and the conductive electrodes  110 ,  112 . The light conversion coating  120  exposes a portion of two of the conductive electrodes  110 ,  112 . The light conversion coating  120  comprises an adhesive  122  and a plurality of phosphors  124 . 
     LED filament  100  emits light while the conductive electrodes  110 ,  112  are applied with electrical power (electrical current sources or electrical voltage sources). In this embodiment, the light emitted from the LED filament  100  is substantially close to 360 degrees light like that from a point light source. An LED light bulb  10   a ,  10   b , illustrated is in  FIGS. 12A and 12B , utilizing the LED filament  100  is capable of emitting omnidirectional light, which will be described in detailed in the followings. 
     As illustrated in the  FIG. 1 , the cross-sectional outline of the LED filament  100  is rectangular. However, the cross-sectional outline of the LED filament  100  is not limited to rectangular, but may be triangle, circle, ellipse, square, diamond, or square with chamfers. 
     Each of LED chips  102 ,  104  may comprise a single LED die or a plurality of LED dies. The outline of the LED chip  102 ,  104  may be, but not limited to, a strip shape which does not have the problem of current diffusion uniform distribution. Therefore, extended electrodes are not required on the electrodes of the LED chip  102 ,  104  to help the current diffusion. The extended electrodes may shield the illumination of the LED chip, thereby affecting the illumination efficiency. In addition, the LED chips  102 ,  104  may be coated on their surfaces with a conductive and transparent layer of Indium Tim Oxide (ITO). The metal oxide layer contributes to uniform distribution of the current diffusion and to increase of illumination efficiency. Specifically, the aspect ratio of the LED chip may be 2:1 to 10:1; for example, but not limited to, 14×28 or 10×20. Further, the LED chips  102 ,  104  may be high power LED dies and are operated at low electrical current to provide sufficient illumination but less heat. 
     The LED chips  102 ,  104  may comprise sapphire substrate or transparent substrate. Consequently, the substrates of the LED chips  102 ,  104  do not shield/block light emitted from the LED chips  102 ,  104 . In other words, the LED chips  102 ,  104  are capable of emitting light from each side of the LED chips  102 ,  104 . 
     The electrical connections among the plurality of LED chips  102 ,  104  and the conductive electrodes  112 ,  114 , in this embodiment, may be shown in  FIG. 1 . The LED chips  102 ,  104  are connected in series and the conductive electrodes  112 ,  114  are disposed on and electrically and respectively connected with the two ends of the series-connected LED chips  102 ,  104 . However, the connections between the LED chips  102 ,  104  are not limited to that in  FIG. 1 . Alternatively, the connections may be that two adjacent LED chips  102 ,  104  are connected in parallel and then the parallel-connected pairs are connected in series. 
     According to this embodiment, the conductive electrodes  110 ,  112  may be, but not limited to, metal electrodes. The conductive electrodes  110 ,  112  are disposed at two ends of the series-connected LED chips  102 ,  104  and a portion of each of the conductive electrodes  110 ,  112  are exposed out of the light conversion coating  120 . In an embodiment of at least three conductive electrodes  110 ,  112 , a portion of two of the conductive electrodes  110 ,  112  are exposed out of the light conversion coating  120 . Please refer to  FIGS. 3A and 3B  which illustrate disposition of metal electrodes and a plurality of LED chips according to other embodiments of the LED filament. In the embodiment of  FIG. 3A , the LED chips  102 ,  104  are connected in series and the two ends of the series-connected LED chips  102 ,  104  are positioned at the same side of the LED filament  100  to form an U shape. Accordingly, the two conductive electrodes  110 ,  112  are positioned at the same side as the ends of the series-connected LED chips  102 ,  104 . According to the embodiment of  FIG. 3B , the LED chips  102 ,  104  are disposed along two parallel LED strips and the LED chips  102 ,  104  along the same LED strip are connected in series. Two conductive electrodes  110 ,  112  are disposed at two ends of the series-connected LED chips  102 ,  104  and electrically connected to each of ends of the series-connected LED chips  102 ,  104 . In this embodiment of  FIG. 3B , there are, but not limited to, only two conductive electrodes  110 ,  112 . For examples, the LED filament  100 , in practices, may comprise four sub-electrodes. The four sub-electrodes are connected to four ends of the series-connected LED chips  102 ,  104 , respectively. The sub-electrodes may be connected to anode and ground as desired. Alternatively, one of two conductive electrodes  110 ,  112  may be replaced with two sub-electrodes, depending upon the design needs. 
     Please further refer to  FIG. 12A . The conductive electrodes  110 ,  112  has through holes  111 ,  113  (shown in  FIG. 1 ) on the exposed portion for being connected with the conductive supports  14   a ,  14   b  of the LED light bulb  10   a.    
     Please refer to  FIGS. 1 and 2  again. According to this embodiment, the LED filament  100  further comprises conductive wires  140  for electrically connecting the adjacent LED chips  102 ,  104  and conductive electrodes  110 ,  112 . The conductive wires  140  may be gold wires formed by a wire bond of the LED package process, like Q-type. According to  FIG. 2 , the conductive wires  140  are of M shape. The M shape here is not to describe that the shape of the conductive wires  140  exactly looks like letter M, but to describe a shape which prevents the wires from being tight and provides buffers when the conductive wires  140  or the LED filament  100  is stretched or bended. Specifically, the M shape may be any shape formed by a conductive wire  140  whose length is longer than the length of a wire which naturally arched between two adjacent LED chips  102 ,  104 . The M shape includes any shape which could provide buffers while the conductive wires  104  are bended or stretched. 
     The light conversion coating  120  comprises adhesive  122  and phosphors  122 . The light conversion coating  120  may, in this embodiment, wrap or encapsulate the LED chips  102 ,  104  and the conductive electrodes  110 ,  112 . In other words, in this embodiment, each of six sides of the LED chips  102 ,  104  is coated with the light conversion coating  120 ; preferably, but not limited to, is in direct contact with the light conversion coating  120 . However, at least two sides of the LED chips  102 ,  104  may be coated with the light conversion coating  120 . Preferably, the light conversion coating  120  may directly contact at least two sides of the LED chips  102 ,  104 . The two directly-contacted sides may be the major surfaces which the LED chips emit light. Referring to  FIG. 1 , the major two surfaces may be the top and the bottom surfaces. In other words, the light conversion coating  120  may directly contact the top and the bottom surfaces of the LED chips  102 ,  104  (upper and lower surfaces of the LED chips  102 ,  104  shown in  FIG. 2 ). Said contact between each of six sides of the LED chips  102 ,  104  and the light conversion coating  120  may be that the light conversion coating  120  directly or indirectly contacts at least a portion of each side of the LED chips  102 ,  104 . Specifically, one or two sides of the LED chips  102 ,  104  may be in contact with the light conversion coating  120  through die bond glue. In some embodiments, the die bond glue may be mixed with phosphors to increase efficiency of light conversion. The die bond glue may be silica gel mixed with silver powder or heat dissipating powder to increase effect of heat dissipation thereof. The adhesive  122  may be silica gel. In addition, the silica gel may be partially or totally replaced with polyimide or resin materials to improve the toughness of the light conversion coating  120  and to reduce possibility of cracking or embrittlement. 
     The phosphors  124  of the light conversion coating  120  absorb some form of radiation to emit light. For instance, the phosphors  124  absorb light with shorter wavelength and then emit light with longer wavelength. In one embodiment, the phosphors  124  absorb blue light and then emit yellow light. The blue light which is not absorbed by the phosphors  124  mixes with the yellow light to form white light. According to the embodiment where six sides of the LED chips  102 ,  104  are coated with the light conversion coating  120 , the phosphors  124  absorb light with shorter wavelength out of each of the sides of the LED chips  102 ,  104  and emit light with longer wavelength. The mixed light (longer and shorter wavelength) is emitted from the outer surface of the light conversion coating  120  which surrounds the LED chips  102 ,  104  to form the main body of the LED filament  100 . In other words, each of sides of the LED filament  100  emits the mixed light. 
     The light conversion coating  120  may expose a portion of two of the conductive electrodes  110 ,  112 . Phosphors  124  is harder than the adhesive  122 . The size of the phosphors  124  may be 1 to 30 um (micrometer) or 5 to 20 um. The size of the same phosphors  124  are generally the same. In  FIG. 2 , the reason why the cross-sectional sizes of the phosphors  124  are different is the positions of the cross-section for the phosphors  124  are different. The adhesive  122  may be transparent, for example, epoxy resin, modified resin or silica gel, and so on. 
     The composition ratio of the phosphors  124  to the adhesive  122  may be 1:1 to 99:1, or 1:1 to 50:1. The composition ratio may be volume ratio or weight ratio. Please refer to  FIG. 2  again. The amount of the phosphors  124  is greater than the adhesive  122  to increase the density of the phosphors  124  and to increase direct contacts among phosphors  124 . The arrow lines on  FIG. 2  show thermal conduction paths from LED chips  102 ,  104  to the outer surfaces of the LED filament  100 . The thermal conduction paths are formed by the adjacent and contacted phosphors. The more direct contacts among the phosphors  124 , the more thermal conduction paths forms, the greater the heat dissipating effect the LED filament  100  has, and the less the light conversion coating becomes yellow. Additionally, the light conversion rate of the phosphors  124  may reach 30% to 70% and the total luminance efficiency of the LED light bulb  10   a ,  10   b  is increased. Further, the hardness of the LED filament  100  is increased, too. Accordingly, the LED filament  100  may stand alone without any embedded supporting component like rigid substrates. Furthermore, the surfaces of cured LED filament  100  are not flat due to the protrusion of some of the phosphors  124 . In other words, the roughness of the surfaces and the total surface area are increased. The increased roughness of the surfaces improves the amount of light passing the surfaces. The increased surface area enhances the heat dissipating effect. As a result, the overall luminance efficiency of the LED light filament  100  is raised. 
     Next, LED chips  102 ,  104  may comprise LED dies which emit blue light. The phosphors  124  may be yellow phosphors (for example Garnet series phosphors, YAG phosphors), so that the LED filament  100  may emit white light. In practices, the composition ratio of phosphors  124  to the adhesive  122  may be adjusted to make the spectrum of the white light emitted from the LED filament  100  closer to that emitted from incandescent bulbs. Alternatively, the phosphors  124  may be powders which absorb blue light (light with shorter wavelength) and emit yellow green light (hereinafter referred to yellow green powders) or emit red light (hereinafter referred to red powders) (light with longer wavelength). The light conversion coating  120  may comprise less red powders and more yellow green powders, so that the CCT (corrected color temperature) of the light emitted from the LED filament  100  may close to 2,400 to 2,600 K (incandescent light). 
     As mention above, a desired deflection of the LED filament  100  may be achieved by the adjustment of the ratio of phosphors  124  to the adhesive  122 . For instance, the Young&#39;s Modulus (Y) of the LED filament  100  may be between 0.1×10 10  to 0.3×10 10  Pa. If necessary, the Young&#39;s Modulus of the LED filament  100  may be between 0.15×10 10  to 0.25×10 10  Pa. Consequently, the LED filament  100  would not be easily broken and still possess adequate rigidity and deflection. 
     Please refer to  FIGS. 4 to 5 .  FIG. 4  illustrates a perspective view of an LED light bulb with partial sectional view according to a second embodiment of the LED filament and  FIG. 5  illustrates a partial cross-sectional view at section  5 - 5  of  FIG. 4 . 
     According to the second embodiment of the LED filament  200 , the LED filament  200  comprises a plurality of LED chips  202 ,  204 , at least two conductive electrodes  210 ,  212 , and a light conversion coating  220 . The conductive electrodes  210 ,  212  are disposed corresponding to the plurality of LED chips  202 ,  204 . The plurality of LED chips  202 ,  204  and the conductive electrodes  212 ,  214  are electrically connected therebetween. The light conversion coating  220  coats on at least two sides of the LED chips  202 ,  204  and the conductive electrodes  210 ,  212 . The light conversion coating  220  exposes a portion of two of the conductive electrodes  210 ,  212 . The light conversion coating  220  comprises an adhesive  222 , a plurality of inorganic oxide nanoparticles  226  and a plurality of phosphors  224 . 
     The size of the plurality of inorganic oxide nanoparticles  226  is around 10 to 300 nanometers (nm) or majorly is around 20 to 100 nm. The size of the plurality of inorganic oxide nanoparticles  226  is lesser than that of the phosphors  224 . The plurality of the inorganic oxide nanoparticles  226  may be, but not limited to, aluminium oxides (Al 2 O 3 ), silicon oxide (SiO 2 ), zirconium oxide (Zirconia, ZrO 2 ), titanic oxide (TiO 2 ), Calcium oxide (CaO), strontium oxide (SrO), and Barium oxide (BaO). 
     As shown in  FIG. 5 , the inorganic oxide nanoparticles  226  and the phosphors  224  are mixed with the adhesive  222 . The unit prices and the hardnesses of the inorganic oxide nanoparticles  226  and the phosphors  224  are different. Therefore, a desired deflection, thermal conductivity, hardness, and cost of the LED filament  200  may be reached by adjustment of the ratio of the adhesive  222 , phosphors  224  to the inorganic oxide nanoparticles  226  affects. In addition, due that the size of the inorganic oxide nanoparticles  226  is lesser than that of the phosphors  224 , the inorganic oxide nanoparticles  226  may fill into the gaps among the phosphors  224 . Hence, the contact area among the phosphors  224  and the inorganic oxide nanoparticles  226  is increased and thermal conduction paths are increased as shown by arrow lines on  FIG. 5 , too. Further, the inorganic oxide nanoparticles  226  may deflect or scatter light incident thereon. The light deflection and scattering make the light emitted from phosphors  224  mixed more uniformly and the characteristics of the LED filament  200  becomes even better. Furthermore, the impedance of the inorganic oxide nanoparticles  226  is high and no electrical leakage would happen through the inorganic oxide nanoparticles  226 . 
     In some embodiments, the phosphors  224  are substantially uniformly distributed in the adhesive  222  (for instance, in silica gel, the polyimide or resin materials). Each of the phosphors  224  may be partially or totally wrapped by the adhesive  222  to improve the cracking or embrittlement of the light conversion coating  220 . In the case that not each of the phosphors  224  is totally wrapped by the adhesive  222 , the cracking or embrittlement of the light conversion coating  220  is still improved. In some embodiments, silica gel may be mixed with the polyimide or resin materials to form the light conversion coating  220 . 
     The LED filament  200  further comprises a plurality of circuit film  240  (or call as transparent circuit film) for electrically and correspondingly connected among the plurality of LED chips and the conductive electrodes. Specifically, the plurality of circuit film  240  is electrically connecting the adjacent LED chips  202 ,  204  and conductive electrodes  210 ,  212 . The light conversion coating  220  may encapsulate the plurality of circuit film  240 . 
     Please refer to  FIG. 6A .  FIG. 6A  illustrates a first embodiment of the uncut circuit film according to the second embodiment of the LED filament  200 . Each of the circuit films  240  comprises a first film  242  and a conductive circuit  244  disposed on the first film  242 . The first film  242  in one embodiment may be, but not limited to, a thin film. In order to be easily understood the embodiments, the following description uses thin film as an example for the first film  242 . However, the thin film  242  is not the only embodiment for the first film  242 . The thin film  242  may be a transparent or translucent film. The transparent film may allow light emitted from the LED chips  202 ,  204  and/or phosphors  124  to pass. The conductive circuits  244  are electrically and correspondingly connected among the plurality of LED chips  202 ,  204  and the conductive electrodes  210 ,  212 . In this embodiment, the conductive circuits  244  are of bar shape and substantially parallel to each other. However, the conductive circuits  244  may be in other shape or pattern. Please refer to  FIG. 7A  which illustrates a second embodiment of the uncut circuit film according to the second embodiment of the LED filament. Each of the circuit films  240   a  comprises a thin film  242   a  and a conductive circuit  244   a  disposed on the thin film  242   a . The conductive circuits  244   a  are substantially parallel lines electrically connected with pads of adjacent LED chips  202 ,  204  as shown in  FIG. 7B . Please refer to  FIG. 8A  which illustrates a third embodiment of the uncut circuit film according to the second embodiment of the LED filament. Each of the circuit films  240   b  comprises a thin film  242   b  and a conductive circuit  244   b  disposed on the thin film  242   b . The conductive circuits  244   b  are crossover lines electrically connected with pads of adjacent LED chips  202   b ,  204   b  as shown in  FIG. 8B . The width of the lines may be 10 micrometers (um) and the thickness of the lines may be 2 um. The pattern or shape of the conductive circuits  244 ,  244   a , and  244   b  are not limited to the above-mentioned embodiments, any pattern or shape which is capable of connecting pads of adjacent LED chips  202 ,  204  and conductive electrodes  210 ,  212  are feasible. 
     The thin film  242  may be, but not limited to, Polyimide film (PI film). Transmittance of the polyimide film is above 92%. The material of the conductive circuit  244  may be, but not limited to, indium tin oxide (ITO), nano-silver plasma, metal grids, or nano-tubes. The advantages of Silver include good reflection and low light absorption. Nano-scaled silver lines in grid shape have advantages of low resistance and high penetration of light. In addition, gold-dopped nano-silver lines may enhance the adherence between the pads of the LED chips  202 ,  204  and the sliver lines (conductive circuits). 
     Please refer to  FIG. 6A  again. The circuit film  240  may be made by firstly forming conductive circuits  244  on a thin film  242 , and then forming slots  246  on the thin film  242  with the conductive circuits  244 . 
     Please refer to  FIG. 6A . The conductive circuits  244  do not cover the whole surface of the thin film  242 . Consequently, light emitted from the LED chips  202 ,  204  can pass through the circuit film  240  at least from the portion of the thin film  242  where the conductive circuits  244  do not occupy. In the second embodiment, the circuit film  240  is used to electrically connect with adjacent LED chips  202 ,  204  and the conductive electrodes  210 ,  212 . The circuit film  240  has the advantages of wider conductive lines, better deflection, and better toughness (less possibility of being broken) than the conductive wires  140  in the first embodiments. 
     Regarding the electrical connection among the circuit film  240 , LED chips  202 ,  204 , and the conductive electrodes  210 ,  212 , conductive glues may be applied on the surfaces of the LED chips  202 ,  204  and the conductive electrodes  210 ,  212  where the conductive circuits  244  are going to electrically connect. The conductive glues may be, but not limited to, silver paste, solder paste (tin paste), or conductive glues doped with conductive particles. Then, dispose the circuit film  240  on the LED chips  202 ,  204  and the conductive electrodes  210 ,  212  with adequate alignment and cure the circuit film  240  and the conductive glues by heat or UV. 
     Please refer to  FIGS. 9A to 9E  which illustrate a manufacturing method of an LED filament according to a first embodiment. The manufacturing method of the LED filament  200  comprises: 
     S 20 : dispose LED chips  202 ,  204  and at least two conductive electrodes  210 ,  210  on a carrier  280 , referring to  FIG. 9A ; 
     S 22 : electrically connect the LED chips  202 ,  204  with the conductive electrodes  210 ,  212 , referring to  FIG. 9B ; and 
     S 24 : dispose a light conversion coating  220  on the LED chips  202 ,  204  and the conductive electrodes  210 ,  212 . The light conversion coating  220  coats on at least two sides of the LED chips  202 ,  204  and the conductive electrodes  210 ,  212 . The light conversion coating  220  exposes a portion of at least two of the conductive electrodes  210 ,  212 . The light conversion coating  220  comprises adhesive  222  and a plurality of phosphors  224 , referring to  FIGS. 9C to 9E . 
     In S 20 , the plurality of LED chips  202 ,  204  are disposed in a rectangular array. Each column of the LED chips  202 ,  204 , at the end of the manufacturing process, may be cut into a single LED filament  200 . During disposition of the LED chips  202 ,  204 , the anodes and cathodes of the LED chips  202 ,  204  should be properly orientated for later connected in series or parallel. The carrier  280  may be, but not limited to, glass substrate or metal substrate. The carrier  280  may be, but not limited to, a plate like that shown in  FIG. 9A , or a plate with a groove like the carrier  180  shown in  FIG. 10 . The groove is for being disposed with the base layer  120   b.    
     In S 22 , the uncut circuit film  240   a  is similar to the circuit film  240   a  shown in  FIG. 7A . The LED chips  202 ,  204  and the conductive circuit  210 ,  212  are electrically connected by the parallel conductive lines. Alternatively, the circuit film  240 ,  240   b  shown, respectively, in  FIG. 6A or 8A  may be used in S 22 . The conductive wires  140  shown in  FIG. 2  can be used in S 22 , too. 
     In S 24 , the light conversion coating  220  may be coated on the LED chips  202 ,  204  and the conductive electrodes  210 ,  212  by different method. Firstly, taking  FIGS. 9C to 9E  as an example, the manufacturing method of S 24  comprises: 
     S 240 : coat a light conversion sub-layer (top layer  220   a ) on a surface of the LED chips  202 ,  204  and the conductive electrodes  210 ,  212  which is not contact with the carrier  280 ; 
     S 242 : flip over the LED chips  202 ,  204  and the conductive electrodes  210 ,  212  disposed with the top layer  220   a ; and 
     S 244 : coat a light conversion sub-layer (base layer  220   b ) on a surface of the LED chips  202 ,  204  and the conductive electrodes  210 ,  212  which are not coated with the top layer  220   a.    
     In order to distinguish the light conversion sub-layers in S 240  and in S 244 , the light conversion sub-layer in S 240  is referred to top layer  220   a  and the light conversion sub-layer in S 244  is referred to base layer  220   b  hereinafter. 
     In S 240 , after the LED chips  202 ,  204  and the conductive electrodes  210 ,  212  are coated with the top layer  220   a , the adhesive  222  and the phosphors  224  will fill out the gaps among the LED chips  202 ,  204  and the conductive electrodes  210 ,  212 . Then, proceed with a curing process to harden the top layer which encapsulates the upper part of the LED chips  202 ,  204  and the conductive electrodes  210 ,  212  and exposes a portion of at least two of the conductive electrodes  210 ,  212 . The curing process may be done by heat or UV. 
     In S 242 , the flip-over of the semi-finished piece may be done by two different ways in accordance with different situations. Concerning the first flip-over way, the LED chips  202 ,  204  and the conductive electrodes  210 ,  212  are disposed on the carrier  280  without any adherences with the carrier  280 . S 242  can be done by flip the cured semi-finished piece over directly. Then, place the flipped-over semi-finished piece on the carrier  280  again. (The semi-finished piece is the cured the LED chips  202 ,  204  and the conductive electrodes  210 ,  212  covered with the top layer  220   a .) 
     As for the second way, glues are applied on the carrier  280 . The glues are, for instance, photoresist in semiconductor process, or die bond glues. The glues (photoresist or die bond glues) is for temporarily fixing the LED chips  202 ,  204  and the conductive electrodes  210 ,  212  on the carrier  280 . The glue may be removed by acetone or solvent and the semi-finished piece is separated from the carrier  280 . If necessary, the remained glues may be removed by an additional cleaning process. 
     In S 244 , referring to  FIG. 9E , cure the base layer  220   b  after the base layer  220   b  is coated on the surface of the LED chips  202 ,  204  and the conductive electrodes  210 ,  212 . 
     Referring to  FIG. 9C , the top layer  220   a  is slightly greater than the uncut circuit film  240   a . However, it is not a requirement. The sizes of the top layer  220   a  may be the same as or lesser than that of the uncut circuit film  240   a . Referring to  FIG. 9E , the area of the top layer  220   a  is substantially the same as that of the base layer  220   b . It is not a requirement, either. In implementation, the area of the top layer  220   a  may be greater or lesser than the area of the base layer  220   b .  FIG. 9E  illustrates a semi-finished LED filament where a plurality of LED filaments  200  are integrated into one piece. 
     After S 24 , the method may further comprise S 26 : cut the semi-finished LED filament along the dot-and-dash lines shown in  FIG. 9E . Each cut portion is an LED filament  200 . The semi-finished LED may be cut every other two dot-and-dash lines. 
       FIGS. 6B, 7B and 8B  illustrate uncut circuit films  240 ,  240   a ,  240   b  of  FIGS. 6A, 7A and 8A  covering the LED chips  202 ,  204  and the conductive electrodes  210 ,  212  with proper alignment. 
     The method of  FIGS. 9A to 9E  illustrates each LED filament are disposed in a rectangular array manner. Alternatively, the disposition of S 20  may be a single column of LED chips  202 ,  204 . In the consequence, S 26  may be omitted. 
     Please refer to  FIG. 10  for the second embodiment of the manufacturing method for the LED filament  200 . The method comprises: 
     S 20 A: coat a light conversion sub-layer (a base layer  120   b ) on a carrier  180 ; 
     S 20 B: dispose LED chips  102 ,  104  and conductive electrodes  110 ,  112  on the base layer  120   b;    
     S 22 : electrically connect the LED chips  102 ,  104  with the conductive electrodes  110 ,  112 ; and 
     S 24 : coat a light conversion sub-layer (top layer  120   a ) on the LED chips  102 ,  104  and the conductive electrodes  110 ,  112 . The top layer  120   a  coats on the LED chips  102 ,  104  and the conductive electrodes  110 ,  112 . The top layer  120   a  and the base layer  120   b  expose a portion of at least two of the conductive electrodes  110 ,  112 . The light conversion coating  120  (top layer  120   a  and the base layer  120   b ) comprises adhesive  122  and a plurality of phosphors  124 . 
     As shown in  FIG. 10 , the base layer  120   b  is a part of the light conversion coating  120  and comprises an adhesive  122  and phosphors  124 . In the embodiment of  FIG. 10 , the base layer  120   b  is, but not limited to, coated on the carrier  180  with a groove. Alternatively, the carrier  180  can be omitted. In other words, the base layer  120   b  may be place on a work table without any carrier  180 . The LED chips  102 ,  104  and the conductive electrodes  110 ,  112  are disposed on the base layer  120   b.    
     The thickness of the base layer  120   b  may be 50 to 100 um. The composition ratio of phosphors  124  to the adhesive  122  can be adjusted and the thickness of the base layer  120   b  may be around 60 to 80 um. After S 20 , a pre-curing process may be used to slightly cure the base layer  120   b  so that the LED chips  102 ,  104  and the conductive electrodes  110 ,  112  can be fixed on the base layer  120   b . Besides, the LED chips  102 ,  104  and the conductive electrodes  110 ,  112  may be fixed on the base layer  120   b  by die bond glues. 
     After the electrical connection of S 22 , the top layer  120   a  is coated on the LED chips  102 ,  104  and the conductive electrodes  110 ,  112  and then a curing process is proceeded with to cure the top layer  120   a . Consequently, the flip-over of S 242  and glue-removing process are omitted. 
     According to the embodiment of  FIG. 10 , after S 24 , the process of S 26  may be proceeded with. 
     The base layer  120   b  is used for carrying the LED chips  102 ,  104  and the conductive electrodes  110 ,  112  and its thickness may be 0.5 to 3 millimeter (mm) or 1 to 2 mm. 
     The composition ratio of phosphors  124  to the adhesive  122  may be adjusted accordingly to make the base layer  120   b  hard enough to sufficiently carry the LED chips  102 ,  104  and the conductive electrodes  110 ,  112  and for the following process like wire bond. The Shore D Hardness of the base layer  120   b  may be at least 60 HD. Hence, the overall LED filament  10   a  will have enough hardness, rigidity and deflection. The electrical conductivity of the connection among the LED chips  102 ,  104  and the conductive electrodes  110 ,  112  can be maintained even though the LED filament  10   a  is bent. 
     In accordance with the embodiment of  FIG. 10 , the hardness of the cured base layer  120   b  is better to be sufficient to carry the LED chips  102 ,  104  and the conductive electrodes  110 ,  112  and to support for the wire bonding process. However, the top layer  120   a  is not required to have the same hardness as the base layer  120   b . Accordingly, the adjustment of ratio of the phosphors  124  to the adhesive  122  is more flexible. Alternatively, the light conversion coating  120  may comprise inorganic oxide nanoparticles  224  (not shown in  FIG. 10 ). 
     Next, please refer to  FIGS. 11A to 11D  which illustrate a manufacturing method of an LED filament according to a third embodiment. The manufacturing method for an Led filament  10   a  comprises: 
     S 202 : dispose conductive foil  130  on a light conversion sub-layer (base layer  120   b ), referring to  FIG. 11A ; 
     S 204 : dispose a plurality of LED chips  102 ,  104  and a plurality of conductive electrodes  110 , 112  on the conductive foil  130 , referring to  FIG. 11B ; 
     S 22 : electrically connect the LED chips  102 ,  104  with the conductive electrodes  110 ,  112 , referring to  FIG. 11C ; and 
     S 24 : coat a light conversion sub-layer (top layer  120   a ) on the surfaces of the LED chips  102 ,  104  and the conductive electrode  110 ,  112  where are not in contact with the base layer  120   b . The light conversion coating  120  (including the base layer  120   b  and the top layer  120   a ) coats on at least two sides of the LED chips  102 ,  104  and the conductive electrodes  110 ,  112 . The light conversion coating  120  exposes a portion of at least two of the plurality of conductive electrodes  110 ,  112 . The light conversion coating  120  comprises adhesive  122  and phosphors  124 . 
     Please refer to  FIG. 11A , the light conversion coating of S 202  is called as the base layer  120   b . The conductive foil  130  may have a plurality of openings  132 . The width of each of the openings  132  may be lesser than the length of the LED chips  102 ,  104  and each of the openings  132  is aligned with the portion of the LED chips  102 ,  104  which emits light. Therefore, light emitted from LED may pass through the openings  132  without any shielding or blocking. 
     The conductive foil  130  may be, but not limited to, a copper foil coated with silver. The openings  132  may be formed by punching or stamping on a copper foil. 
     Before S 202 , the method may comprise a pre-step: dispose the base layer  120   b  on a carrier (like  180  of  FIG. 10 ) or on a work table. 
     In S 204 , please refer to  FIG. 11B . The LED chips  102 ,  104  and the conductive electrodes  110 ,  112  are disposed on the conductive foil  130 . As above-mentioned, the light emitting portions of the LED chips  102 ,  104  are better to align with the openings  132 . 
     Please refer to  FIG. 11C . The electrical connection of S 22  may be accomplished by wire bonding process like that shown in  FIG. 1 . As shown in  FIG. 11C , the LED chips  102 ,  104  and the conductive electrodes  110 ,  112  are electrically connected together in series. 
     Next, please refer to  FIG. 11D . Like the embodiment of  FIG. 10 , the light conversion sub-layer may be referred to top layer  120   a . The top layer  120   a  fills out the gaps among the LED chips  102 ,  104  and the conductive electrodes  110 ,  112  including the gaps under the LED chips  102 ,  104  and the openings  132 . 
     Regarding the disposition of the top layer  120   a , there are a few method to proceed with. The first one is to coat a mixture of the adhesive  122  and the phosphors  124  on the LED chips  102 ,  104  and the conductive electrodes  110 ,  112 . The second one is to firstly coat a layer of adhesive  122  on the LED chips  102 ,  104  and the conductive electrodes  110 ,  112 , and secondly coat a layer of phosphors  124  on the layer of the adhesive  122  (two disposition steps). Thereafter, cure the layer of adhesive  122  and the layer of phosphors  124 . The third one is to repeat the above two disposition steps until a required thickness is reached. Thereafter, a curing process is proceeded with. In comparison with the three methods, the uniformity of the light conversion coating  120  done by the third method might be better. Additionally, the disposition (coat) of the adhesive  122  or the phosphors  124  may be done by spraying. 
     After S 24 , a cut process may be proceeded with, referring to  FIG. 11E . Cut LED filaments  100  are manufactured as shown in  FIG. 11E . 
     In accordance with the embodiment of  FIGS. 11A to 11E , the LED chips  102 ,  104  and the conductive electrodes  110 ,  112  are electrically connected together through conductive foil  130  and conductive wire  140 . The flexibility of the electrical connections is enhanced. Accordingly, when the LED filament  100  is bent, the electrical connections would not be easily broken. 
     Please refer to  FIGS. 12A and 12B  which illustrate a perspective view of LED light bulb applying the LED filaments according to a first and a second embodiments. The LED light bulb  10   a ,  10   b  comprises a bulb shell  12 , a bulb base  16  connected with the bulb shell  12 , at least two conductive supports  14   a ,  14   b  disposed in the bulb shell  12 , a driving circuit  18  electrically connected with both the conductive supports  14   a ,  14   b  and the bulb base  16 , and a single LED filament  100 . 
     The conductive supports  14   a ,  14   b  are used for electrically connecting with the conductive electrodes  110 ,  112  and for supporting the weight of the LED filament  100 . 
     The bulb base  16  is used to receive electrical power. The driving circuit  18  receives the power from the bulb base  16  and drives the LED filament  100  to emit light. Due that the LED filament  100  emits light like the way a point light source does, the LED bulb  10   a ,  10   b  may emit omnidirectional light. In this embodiment, the driving circuit  18  is disposed inside the LED light bulb. However, in some embodiments, the driving circuit  18  may be disposed outside the LED bulb. 
     The definition of the omnidirectional light depends upon the area the bulb is used and varies over time. The definition of the omnidirectional light may be, but not limited to, the following example. Page 24 of Eligibility Criteria version 1.0 of US Energy Star Program Requirements for Lamps (Light Bulbs) defines omnidirectional lamp in base-up position requires that light emitted from the zone of 135 degree to 180 degree should be at least 5% of total flux (Im), and 90% of the measured intensity values may vary by no more than 25% from the average of all measured values in all planes (luminous intensity (cd) is measured within each vertical plane at a 5 degree vertical angle increment (maximum) from 0 degree to 135 degree). JEL 801 of Japan regulates the flux from the zone within 120 degrees along the light axis should be not less than 70% of total flux of the bulb. 
     In the embodiment of  FIG. 12A , the LED light bulb  10   a  comprises two conductive supports  14   a ,  14   b . In an embodiment, the LED light bulb may comprise more than two conductive supports  14   a ,  14   b  depending upon the design. 
     The bulb shell  12  may be shell having better light transmittance and thermal conductivity; for example, but not limited to, glass or plastic shell. Considering a requirement of low color temperature light bulb on the market, the interior of the bulb shell  12  may be appropriately doped with a golden yellow material or a surface inside the bulb shell  12  may be plated a golden yellow thin film for appropriately absorbing a trace of blue light emitted by a part of the LED chips  102 ,  104 , so as to downgrade the color temperature performance of the LED bulb  10   a ,  10   b . A vacuum pump may swap the air as the nitrogen gas or a mixture of nitrogen gas and helium gas in an appropriate proportion in the interior of the bulb shell  12 , so as to improve the thermal conductivity of the gas inside the bulb shell  12  and also remove the water mist in the air. The air filled within the bulb shell  12  may be at least one selected from the group substantially consisting of helium (He), and hydrogen (H2). The volume ratio of Hydrogen to the overall volume of the bulb shell  12  is from 5% to 50%. The air pressure inside the bulb shell may be 0.4 to 1.0 atm (atmosphere). 
     According to the embodiments of  FIGS. 12A and 12B , each of the LED light bulbs  10   a ,  10   b  comprises a stem  19  in the bulb shell  12  and a heat dissipating element  17  between the bulb shell  12  and the bulb base  16 . The LED filament  100  is connected with the stem  19  through the conductive supports  14   a ,  14   b . The stem  19  may be used to swap the air inside the bulb shell  12  with nitrogen gas or a mixture of nitrogen gas and helium gas. The stem  19  may further provide heat conduction effect from the LED filament  100  to outside of the bulb shell  12 . The heat dissipating element  17  may be a hollow cylinder surrounding the opening of the bulb shell  12 , and the interior of the heat dissipating element  17  may be equipped with the driving circuit  18 . The material of the heat dissipating element  17  may be at least one selected from a metal, a ceramic, and a plastic with a good thermal conductivity effect. The heat dissipating element  17  and the stem  19  may be integrally formed in one piece to obtain better thermal conductivity in comparison with the traditional LED light bulb whose thermal resistance is increased due that the screw of the bulb base is glued with the heat dissipating element. 
     Referring to  FIG. 12A , the height of the heat dissipating element  17  is L 1  and the height from the bottom of the heat dissipating element  17  to the top of the bulb shell  12  is L 2 . The ratio of L 1  to L 2  is from 1/30 to 1/3. The lower the ratio, the higher the cutoff angle of illumination of the light bulb. In other words, the lower ratio increases the higher light-emission angle and the light from the bulb is closer to omnidirectional light. 
     Please referring to  FIG. 12B , the LED filament  100  is bent to form a portion of a contour and to form a wave shape. In order to appropriately support the LED filament  100 , the LED light bulb  10   b  further comprises a plurality of supporting arms  15  which are connected with and supports the LED filament  100 . The supporting arms  15  may be connected with the wave crest and wave trough of the waved shaped LED filament  100 . In this embodiment, the arc formed by the filament  100  is around 270 degrees. However, in other embodiment, the arc formed by the filament  100  may be approximately 360 degrees. Alternatively, one LED light bulb  10   b  may comprise two LED filaments  100  or more. For example, one LED light bulb  10   b  may comprise two LED filaments  100  and each of the LED filaments  100  is bent to form approximately 180 degrees arc (semicircle). Two semicircle LED filaments  100  are disposed together to form an approximately 360 circle. By the way of adjusting the arc formed by the LED filament  100 , the LED filament  100  may provide with omnidirectional light. Further, the structure of one-piece filament simplifies the manufacturing and assembly procedures and reduces the overall cost. 
     In some embodiment, the supporting arm  15  and the stem  19  may be coated with high reflective materials, for example, a material with white color. Taking heat dissipating characteristics into consideration, the high reflective materials may be a material having good absorption for heat radiation like graphene. Specifically, the supporting arm  15  and the stem  19  may be coated with a thin film of graphene. 
     Please refer to  FIG. 13A  and  FIG. 14A .  FIG. 13A  illustrates a perspective view of an LED light bulb according to a third embodiment of the present disclosure.  FIG. 14A  illustrates a cross-sectional view of an LED light bulb according to a fourth embodiment of the present disclosure. According to the third embodiment, the LED light bulb  10   c  comprises a bulb shell  12 , a bulb base  16  connected with the bulb shell  12 , two conductive supports  14   a ,  14   b  disposed in the bulb shell  12 , a driving circuit  18  electrically connected with both the conductive supports  14   a ,  14   b  and the bulb base  16 , a stem  19 , supporting arms  15  and a single LED filament  100 . The LED light bulb  10   d  of the fourth embodiment is similar to the third embodiment illustrated in  FIG. 13A  and comprises two LED filaments  100   a ,  100   b  arranged at the different vertical level in  FIG. 14A . The LED filaments  100   a ,  100   b  are bent to form a contour from the top view of  FIG. 14A . 
     The cross-sectional size of the LED filaments  100 ,  100   a ,  100   b  is small than that in the embodiments of  FIGS. 12A and 12B . The conductive electrodes  110 ,  112  of the LED filaments  100 ,  100   a ,  100   b  are electrically connected with the conductive supports  14   a ,  14   b  to receive the electrical power from the driving circuit  18 . The connection between the conductive supports  14   a ,  14   b  and the conductive electrodes  110 ,  112  may be a mechanical pressed connection or soldering connection. The mechanical connection may be formed by firstly passing the conductive supports  14   a ,  14   b  through the through holes  111 ,  113  (shown in  FIG. 1  and secondly bending the free end of the conductive supports  14   a ,  14   b  to grip the conductive electrodes  110 ,  112 . The soldering connection may be done by a soldering process with a silver-based alloy, a silver solder, a tin solder. 
     Similar to the first and second embodiments shown in  FIGS. 12A and 12B , each of the LED filaments  100 ,  100   a ,  100   b  is bent to form a contour from the top view of  FIGS. 13A and 14A . In the embodiments of  FIGS. 13A, 14A , each of the LED filaments  100 ,  100   a ,  100   b  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  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 ,  100   a ,  100   b . Please refer to  FIG. 13B  which illustrates an enlarged cross-sectional view of the dashed-line circle of  FIG. 13A . 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 ,  100   a ,  100   b . 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 ,  100   a ,  100   b . 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 ,  100   a ,  100   b . During manufacturing process, the LED filament  100 ,  100   a ,  100   b  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 ,  100   a ,  100   b  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 ,  100   a ,  100   b.    
     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 the stand  19   a , 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  10   c  are close to that of the traditional light bulb including illumination brightness. The illumination uniformity of LED light bulb  10   c  is better. 
     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 ,  100   a ,  100   b  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  10   c.    
     Since the inner shape (shape of through hole) of the clamping portion  15   a  fits the outer shape of the cross-section of the LED filament  100 , the orientation of the cross-section of the LED filament  100 , if necessary, may be properly adjusted. As shown in  FIG. 13B , the top layer  120   a  is fixed to face around ten o&#39;clock direction such that illumination surfaces of the LED filament  100  are facing substantially the same direction. 
     Please refer to  FIG. 14B  which illustrates the circuit board of the driving circuit of the LED light bulb from the top view of  FIG. 14A  according to the fourth embodiment of the present disclosure. The driving circuit  18  comprises a circuit board  18   a  which is fixed to the bulb base  16 . The conductive supports  14   a ,  14   b  are electrically connected with the circuit board  18   a  and passes through the stand  19   a  to be electrically connected with the conductive electrodes  110 ,  112  of the LED filament  100   a ,  100   b . The circuit board  18   a  comprises notches  18   b . The notches  18   b  are of hook shape. The size of the tip of the notches  18   b  is slightly smaller than that of the cross-section of the conductive supports  14   a ,  14   b  for fixing the conductive supports  14   a ,  14   b . The tip of the notches  18   b  is beneficial to the soldering between the circuit board  18   a  and the conductive supports  14   a ,  14   b.    
     In the embodiments of  FIGS. 13A and 14A , the length of the conductive supports  14   a ,  14   b  is better to meet the below equation to prevent two conductive supports  14   a ,  14   b  from short circuit or to prevent the conductive supports  14   a ,  14   b  from unable to reach the circuit board  18   a.  
 
 L=A +∞( ( B− 3.2) {circumflex over ( )}2+ H {circumflex over ( )}2)
 
     Wherein, referring to  FIG. 14A , 3.2 is the electricity safety spacing; L is the calculated length of the conductive supports  14   a ,  14   b  and its unit is mini-meter; A is the sum of the thickness of the circuit board  18   a  and the height of the portion of the conductive supports  14   a ,  14   b  exposed from the surface of the circuit board  18   a ; B is the horizontal distance between the two conductive supports  14   a ,  14   b ; and H is the height from the circuit board  18   a  to the point the conductive supports  14   a ,  14   b  enters the stem  19 . The actual length of the conductive supports  14   a ,  14   b  may be, but not limited to, between 0.5 L and 2 L, and more particularly between 0.75 L and 1.5 L. 
     In the embodiment of  FIG. 14A , the LED light bulb  10   d  has two LED filaments  100   a ,  100   b  disposed on different vertical levels. The conductive supports  14   a ,  14   b  for the upper LED filaments  100   a  has a length Z=L+Y. Y is the distance between the upper LED filament  100   a  and the lower LED filament  100   b.    
     While the instant disclosure related to an LED filament and LED light bulb has been described by way of examples and in terms of the preferred embodiments, it is to be understood that the instant disclosure needs not be limited to the disclosed embodiments. For anyone skilled in the art, various modifications and improvements within the spirit of the instant disclosure are covered under the scope of the instant disclosure. The covered scope of the instant disclosure is based on the appended claims.