Patent Publication Number: US-11024779-B2

Title: LED device

Description:
RELATED APPLICATION 
     The present invention is a continuation application of U.S. patent application Ser. No. 15/892,344, which is a continuation-in-part application of U.S. patent application Ser. No. 15/868,801. 
    
    
     FIELD OF THE INVENTION 
     The present invention is related to a LED (light emitted diode) device and more particularly related to a LED device using multiple types of phosphor materials. 
     BACKGROUND 
     After years of hard working, LED products have been widely spread over the world. At beginning, the cost of LED products is too high, preventing LED products to be popular. Nowadays, LED product price has lowered to an acceptable level. 
     However, it is always important to further find every aspect to improve such devices, particularly for such worldwide products related to human daily life. Heat efficiency, color rendering index, and more characteristics need to consider when designing LED devices. 
     In the present invention, inventors look deeper into the LED basic structure and finds several inventive points to further improve LED device performance. 
     SUMMARY OF INVENTION 
     According to a first embodiment of the present invention, a LED device includes a LED module, a first fluorescent layer, a second fluorescent layer and a package housing. The LED module includes a first group of LED chips and a second group of LED chips mounted on a substrate for emitting an original light of an original spectrum. For example, the LED chips are mounted on the substrate using Surface Mounting Device (SMD), Chip Scale Packaging (CSP), flip chip packaging, chip on board (COB) or other packaging methods. 
     The first fluorescent layer faces to the first group of LED chips for converting the original light to a first output light of a first spectrum. The second fluorescent layer faces to the second group of LED chips for converting the original light to a second output light of a second spectrum. 
     The package housing has a shape for holding the substrate, the first fluorescent layer and the second fluorescent layer. The first spectrum is partially overlapped with an excitation spectrum of the second fluorescent layer. In other words, when the first output light is emitted into the second fluorescent layer, the first output light may be further converted to a light of the second spectrum. 
     In one embodiment, the package housing has a first container and a second container for placing the first fluorescent layer and the second fluorescent layer respectively. 
     In another embodiment, the package housing has more than two containers for placing the first fluorescent layers and the second fluorescent layer arranged in interleaved manner. With such arrangement, the mixed light may be more smooth. 
     In some embodiments, there is a separating component for preventing the first output light to emit into the second fluorescent layer. 
     In some embodiments, furthermore, the separating component has a reflecting surface for reflecting and guiding the first output light to a predetermined direction. Therefore, for light emitted onto the reflecting surface, the light is redirected to a desired direction, e.g. top of the LED device or to other directions as predetermined light distribution. 
     In some embodiments, the package housing has multiple side walls for reflecting and directing the first output light and the second output light to predetermined directions. 
     In some embodiments, furthermore, the side walls has a convex or a concave structure engaging the first fluorescent layer or the second fluorescent layer. With such arrangement, the first fluorescent layer and the second fluorescent layer may have better reliability on fixing to the substrate. 
     Such convex structure or concave structure provides position limiting effect when materials the fluorescent layers are attached on or into such structures. Particularly, when the fluorescent layers are in gel mode when installed, such fluorescent layer flow and fit the surface of the concave or convex structures, forming a well holding structure. 
     In some embodiment, the first fluorescent layer has a first convex surface on top of the first fluorescent layer, the second fluorescent layer has a second convex surface on top of the second fluorescent layer. 
     In such design, the first convex surface and the second convex surface form lens guiding the first output light and the second output light for mixing the first output light and the second output light. Light paths may be well optimized for different light devices by adjusting the curve ratio, e.g. to form a condensed beam or a diversified light. 
     Except convex surface, in some other embodiments, the first fluorescent layer may have a first concave surface on top of the first fluorescent layer, and the second fluorescent layer has a second concave surface on top of the second fluorescent layer. 
     In some embodiments, the first output light, the second light and the original light not absorbed by the first fluorescent layer and the second fluorescent layer form an overall output spectrum of a white light. 
     Specifically, in some embodiments, the first fluorescent layer and the second fluorescent layer both comprise red phosphor material for generating 640-650 nm output light. In some other embodiments, the first fluorescent layer and the second fluorescent layer both comprise red phosphor material for generating 628-635 nm output light. 
     Please be noted that red, blue or green phosphor refer to phosphor material for emitting red, blue or green light, instead of defining the color of the phosphor materials themselves. 
     In some embodiments, the original spectrum is substantially corresponding to a blue light, the first spectrum is substantially corresponding to a green light, and the second spectrum is substantially corresponding to a red light. 
     In some other embodiments, the original spectrum is substantially corresponding to a ultraviolet light, the first fluorescent layer comprises green phosphor material and blue phosphor material for generating a green light and a blue light, the second fluorescent layer comprises red phosphor material for generating a red light. 
     In some other embodiments, the original spectrum is substantially corresponding to a ultraviolet light, the first fluorescent layer comprises green phosphor material and red phosphor material for generating a green light and a red light, the second fluorescent layer comprises blue phosphor material for generating a blue light. 
     In some embodiments, the first fluorescent layer and the second fluorescent layer have phosphor material, and the phosphor material has larger density near bottom than top in the first fluorescent layer and the second fluorescent layer. This increases better light efficacy because the bottom part of the first and the second fluorescent layers are closer to the light source, thus increasing phosphor excitation efficiency. 
     In some embodiments, the second fluorescent layer has a larger area than the first fluorescent layer. 
     In some embodiments, the second group of LED chips have more LED chips than the first group of LED chips. 
     According to another embodiment of the present invention, a LED (light emitted diode) device is provided. The LED device has a LED module, a first fluorescent layer, a second fluorescent layer, and a package housing. 
     The LED module is mounted on a substrate for emitting a blue light. 
     The first fluorescent layer has a first side facing to the LED module for converting the blue light to a red light. 
     The second fluorescent layer has a first side attached to a second side of the first fluorescent layer for converting the blue light to a red light emitted from a second side of the second fluorescent layer. 
     The package housing holds the substrate and the first fluorescent layer. 
     With such design, the first fluorescent layer is between the second fluorescent layer and the LED module. In other words, a blue light emitted from the LED module firstly enters the first fluorescent layer, hitting certain phosphor material and generating corresponding red light. In addition, some part of the blue light further moves to the second fluorescent layer to hit other phosphor material to generate green light. With red light and green light, users may see a white light effect. 
     In some embodiments, the LED module has multiple LED chips emitting the blue light. The substrate has a first terminal area and a second terminal area for mounting the multiple LED chips. For example, multiple LED chips are mounted on conductive plates used as the terminal areas with surface mounting device (SMD) technology. 
     The first terminal area and the second terminal area are provided for respectively connected to a positive terminal and a negative terminal of a power source. The first terminal area may have different size as the second terminal area. For example, when there are more LED chips mounted on the first terminal area than on the second terminal area, the first terminal area may have a larger size than the second terminal area to provide better heat dissipation effect. 
     In some embodiments, the first fluorescent has red phosphor material contained in first silicone part, and the second fluorescent layer has green phosphor material contained in a second silicone part. Please be noted that other materials in addition to silica gel, like resin, may be used for containing phosphor powder. 
     In addition, a part of the green light may excite the red phosphor if the green light hits the red phosphor. In other words, if the blue light firstly enters the second fluorescent layer, the blue light may firstly be converted to green light. If such green light continues to move into the first fluorescent layer, part or all of the green light may be consumed and converted into red light. This may decrease the overall green light energy and decreases an overall CRI (color rendering index) of the LED device. 
     Therefore, it is beneficial to place the first fluorescent layer between the second fluorescent layer and the LED module, for improving green light output and deceasing undesired consumption of the green light output. 
     Inventors also find that there the volume ratio of phosphor material in the first fluorescent layer and the second fluorescent layer may be adjusted to further improve different characteristics of the LED device. 
     In some cases, a first volume ratio of the red phosphor to the first silicone part is larger than a second volume ratio of the green phosphor to the second silicone part. 
     In some other cases, a first volume ratio of the red phosphor to the first silicone part is smaller than a second volume ratio of the green phosphor to the second silicone part. 
     The provide different features and characteristics, suitable for making various LED products. 
     In some embodiments, a thickness of the first fluorescent layer is larger than a thickness of the second fluorescent layer. 
     In some other embodiments, a thickness of the first fluorescent layer is smaller than a thickness of the second fluorescent layer. 
     Such variations are found helpful for adjusting product characteristic of the LED device. 
     In addition, the first fluorescent layer may have better heat resisting feature than the second fluorescent layer, when the first fluorescent layer is placed closer to the LED module. In other words, designers may place phosphor material with less heat resisting characteristic as the second fluorescent layer. 
     In some embodiments, the package housing may have a bottom part fixed to the substrate and the package housing has a surrounding wall extended from the bottom part. The wall defines a containing space for holding the first fluorescent layer. 
     For example, the package housing has a hole for holding the substrate and four connecting walls forming a rectangular containing space. The first fluorescent layer and sometimes the second florescent layer are placed in the containing space. 
     There are several ways to design the second fluorescent layer. 
     In some embodiments, a second side of the second fluorescent layer has a curved surface. In other words, the top surface of the second fluorescent layer may have a curve surface. 
     Specifically, an angle of edges of the first side and the second side of the second fluorescent layer would be less than 60 degrees. Such design may increase overall product stability. 
     In some embodiments, the curve surface forms a convex lens, providing better optical characteristic for output light, by directing light to desired direction. 
     According to another embodiment of the present invention, a LED device includes a LED module, a first fluorescent layer, and a second fluorescent layer. 
     The LED module includes a plurality of LED components mounted on a substrate for emitting an original light of an original spectrum. 
     The first fluorescent layer surrounds the plurality of LED components for converting the original light to a first output light of a first spectrum. The second fluorescent layer is stacked on the first fluorescent layer for converting the original light not absorbed by the first fluorescent layer and entering the second fluorescent layer to a second output light of a second spectrum. In addition, the second spectrum is partially overlapped with an excitation spectrum of the second fluorescent layer. 
     In some embodiment, the LED device further includes a package housing for holding the substrate and the first fluorescent layer. The substrate has a plurality of electrode pads. The plurality of LED components are attached to the plurality of electrode pads and electrically connected with wires. The electrode pads are connected to an external power source to drive the LED components to emit the original light. 
     In some embodiments, the LED components are LED semiconductor chips mounted on the substrate using chip-on-board packaging. 
     In some other embodiments, the LED component is made with CSP (Chip Scale Package). In addition, the LED device may include a package housing with reflecting walls for reflecting the original light, the first output light, the second output light to predetermined directions. On designing the angle of the reflecting walls, the second output light is prevented to enter the first fluorescent layer to cause energy waste and total output of the second output light. 
     In some other embodiments, the substrate is an elongated strip. Such elongated strip with LED modules may be used for manufacturing various bulbs emulating the shape of traditional bulbs. In addition, when the substrate is transparent, e.g. glass material, the LED device may further have a third fluorescent layer attaching to a backside of the elongated strip for converting the original light passing through the elongated strip to a third output light of the first spectrum, and a fourth fluorescent layer stacked on the third fluorescent layer for converting the original light not absorbed by the third fluorescent layer and entering the fourth fluorescent layer to a fourth output light of the second spectrum. 
     In some other embodiments, the substrate is a flexible circuit board substrate. 
     In some embodiments, the LED device may further have a side wall fixed to the substrate. The side wall has a convex structure or a concave structure engaging the second fluorescent layer. Such convex structure and concave structure may also be used for fixing the first fluorescent layer. This is particularly helpful when the first fluorescent layer and the second fluorescent layer are heated to gel mode during manufacturing. It is difficult to control the surface temperature of the fluorescent layers to be attached together. With such structures, the fluorescent layers are fixed more reliably. 
     In some embodiments, the first fluorescent layer has a first convex surface on top of the first fluorescent layer, the second fluorescent layer has a second convex surface on top of the second fluorescent layer. The first convex surface and the second convex surface may forming one or more lens guiding the first output light and the second output light for mixing the first output light and the second output light. 
     In some other embodiments, the first fluorescent layer has a first concave surface on top of the first fluorescent layer, the second fluorescent layer has a second concave surface on top of the second fluorescent layer. 
     In some embodiments, there is a boundary surface between the first fluorescent layer and the second fluorescent layer, and the boundary surface is a convex surface facing to the LED module. 
     In some other embodiments, the boundary surface between the first fluorescent layer and the second fluorescent layer is a concave surface facing to the LED module. 
     In some embodiments, the first output light, the second light and the original light not absorbed by the first fluorescent layer and the second fluorescent layer form an overall output spectrum of a white light. 
     Furthermore, in some embodiments, the first fluorescent layer and the second fluorescent layer both include red phosphor material for generating 640-650 nm output light. 
     In some other embodiments, the first fluorescent layer and the second fluorescent layer both include red phosphor material for generating 628-635 nm output light. 
     In some embodiments, there is an intermediate part between the first fluorescent layer and the second fluorescent layer. The intermediate part includes mixed materials of the first fluorescent layer and the second fluorescent layer. The thickness of the intermediate part may be less than 10% of the total width of the first fluorescent layer and the second fluorescent layer. The intermediate part has a plurality of micro convex structures between the first fluorescent layer and the second fluorescent layer. Such convex structures may form a plurality of micro optical lens for better distribute light paths. 
     In another embodiment according to the present invention, a LED device includes a LED module, a first fluorescent layer and a second fluorescent layer. 
     The LED module includes a plurality of LED components mounted on a substrate for emitting an original light of an original spectrum. The first fluorescent layer surrounds the plurality of LED components for converting the original light to a first output light of a first spectrum. The second fluorescent layer is stacked on the first fluorescent layer for converting the original light not absorbed by the first fluorescent layer and entering the second fluorescent layer to generate a second output light of a second spectrum. 
     The second spectrum is partially overlapped with an excitation spectrum of the first fluorescent layer. In addition, there is an intermediate part between the first fluorescent layer and the second fluorescent layer. The intermediate part includes mixed materials of the first fluorescent layer and the second fluorescent layer. The intermediate part has a plurality of micro convex structures between the first fluorescent layer and the second fluorescent layer. 
     In some embodiments, the first fluorescent layer is a dome shape and the second fluorescent layer and the substrate surround the first fluorescent layer. 
     In some embodiments, the LED device further includes a package housing, wherein the package housing and the substrate form a container for storing the first fluorescent layer. 
     In some embodiments, he package housing has a surrounding side wall with larger peripheral size at top than at bottom, e.g. like an inverted pyramid. Such structure further prevents unnecessary waste of the second output light to be emitted into the first fluorescent layer. 
     In some embodiments, the package housing has a surrounding side wall with a reflecting surface facing to the first fluorescent layer. 
     In some embodiments, a heat dissipation material, like powder mixed with metal oxide or metal crystals, may bed mixed in the first fluorescent layer. 
     In some embodiments, the original spectrum is substantially corresponding to a ultraviolet light. The second fluorescent layer contains green phosphor material and blue phosphor material for generating a green light and a blue light, the first fluorescent layer contains red phosphor material for generating a red light. 
     In some embodiments, the LED device may further include a third fluorescent layer containing blue phosphor material for generating blue light spectrum. The second fluorescent layer may contain green phosphor material for generating a green light, and the first fluorescent layer may contain red phosphor material for generating a red light. 
     In some embodiments, the first fluorescent layer may contain red phosphor material and green phosphor material for generating a red light and a green light and the second fluorescent layer may contain blue phosphor material for generating a blue light. 
     In some other embodiments, area of the second side of the second fluorescent layer is smaller than area of the second side of the first fluorescent layer. In other words, when being looked over a top view, a part of the second side of the first fluorescent layer is exposed and uncovered by the second fluorescent layer. 
     In such case, there is an embodiment to place the second fluorescent in the middle place, which causes the second side of second fluorescent layer being surrounded by the second side of the first fluorescent layer from a top view. 
     In some embodiments, the package housing has a ladder wall for engaging with a peripheral part of the second fluorescent layer. In some manufacturing procedures, the first fluorescent layer and the second fluorescent layer are heated as gel mode to be filled into the package holding. When the package holding has a ladder wall, the first fluorescent layer may be filled in a first ladder while the second fluorescent layer may be filled to in a second ladder upper than the first ladder in the ladder wall. 
     In some embodiments, the second side of the second fluorescent layer forms a flat surface. 
     In some other embodiments, the second side of second florescent layer forms a curve surface for different optical characteristic requirement. 
     In some embodiments, the second side of the second fluorescent layer may have multiple convex part corresponding to multiple underlying LED chips of the LED module. It may be implemented by applying gel mode material of the second fluorescent layer to the package for several times respectively to underlying LED chips. Because LED chips usually have certain light emitting angle, it is helpful to maximize the light converting effect by placing more material of the second fluorescent layer on top of corresponding LED chips, particularly when phosphor material is critical cost in LED devices. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating a LED device embodiment. 
         FIG. 2  is a top view of  FIG. 1 . 
         FIG. 3 . Illustrates a first fluorescent layer installed in a LED device embodiment. 
         FIG. 4  illustrates a top view of  FIG. 3 . 
         FIG. 5  illustrates a first way to add a second fluorescent layer. 
         FIG. 6  illustrates a top view of  FIG. 5 . 
         FIG. 7  illustrates another way to add a second fluorescent layer. 
         FIG. 8  illustrates a top view of  FIG. 7 . 
         FIG. 9  illustrates another way to add a second fluorescent layer. 
         FIG. 10  illustrates LED chips in an embodiment. 
         FIG. 11  illustrates another side view of a LED device embodiment. 
         FIG. 12  illustrates a top view of a LED device embodiment. 
         FIG. 13  illustrates a optical characteristic diagram of an experimental result. 
         FIG. 14  illustrates another optical characteristic diagram of an experimental result. 
         FIG. 15A  is a diagram illustrating fluorescent layer shapes of an embodiment. 
         FIG. 15B  is a diagram illustrating fluorescent layer shapes of another embodiment. 
         FIG. 15C  is a diagram illustrating fluorescent layer shapes of another embodiment. 
         FIG. 16A  is a diagram illustrating fluorescent layer curve surfaces of an embodiment. 
         FIG. 16B  is a diagram illustrating fluorescent layer curve surfaces of another embodiment. 
         FIG. 17A  illustrates an auxiliary fixing structure for fixing the fluorescent layer in an embodiment. 
         FIG. 17B  illustrates an auxiliary fixing structure for fixing the fluorescent layer in another embodiment. 
         FIG. 18  illustrates an intermediate part between fluorescent layers. 
         FIG. 19A  illustrates another embodiment of a LED device. 
         FIG. 19B  illustrates another embodiment of a LED device. 
         FIG. 19C  illustrates another embodiment of a LED device. 
         FIG. 20A  illustrates another embodiment of a LED device. 
         FIG. 20B  illustrates another embodiment of a LED device. 
         FIG. 21A  illustrates another embodiment of a LED device. 
         FIG. 21B  illustrates another embodiment of a LED device. 
         FIG. 21C  illustrates another embodiment of a LED device. 
         FIG. 22A  illustrates another embodiment of a LED device. 
         FIG. 22B  illustrates another embodiment of a LED device. 
         FIG. 23A  illustrates another embodiment of a LED device. 
         FIG. 23B  illustrates another embodiment of a LED device. 
         FIG. 23C  illustrates another embodiment of a LED device. 
         FIG. 24  illustrates another embodiment of a LED device. 
         FIG. 25  illustrates another embodiment of a LED device. 
         FIG. 26  illustrates another LED device embodiment. 
         FIG. 27  illustrates another LED device embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     According to an embodiment of the present invention, a LED device includes a LED module, a first fluorescent layer, a second fluorescent layer and a package housing. The LED module includes a first group of LED chips and a second group of LED chips mounted on a substrate for emitting an original light of an original spectrum. For example, the LED chips are mounted on the substrate using Surface Mounting Device (SMD), Chip Scale Packaging (CSP), flip chip packaging, chip on board (COB) or other packaging methods. 
     The first fluorescent layer faces to the first group of LED chips for converting the original light to a first output light of a first spectrum. The second fluorescent layer faces to the second group of LED chips for converting the original light to a second output light of a second spectrum. 
     The package housing has a shape for holding the substrate, the first fluorescent layer and the second fluorescent layer. The first spectrum is partially overlapped with an excitation spectrum of the second fluorescent layer. In other words, when the first output light is emitted into the second fluorescent layer, the first output light may be further converted to a light of the second spectrum. 
     In one embodiment, the package housing has a first container and a second container for placing the first fluorescent layer and the second fluorescent layer respectively. 
     In another embodiment, the package housing has more than two containers for placing the first fluorescent layers and the second fluorescent layer arranged in interleaved manner. With such arrangement, the mixed light may be more smooth. 
     In some embodiments, there is a separating component for preventing the first output light to emit into the second fluorescent layer. 
     In some embodiments, furthermore, the separating component has a reflecting surface for reflecting and guiding the first output light to a predetermined direction. Therefore, for light emitted onto the reflecting surface, the light is redirected to a desired direction, e.g. top of the LED device or to other directions as predetermined light distribution. 
     In some embodiments, the package housing has multiple side walls for reflecting and directing the first output light and the second output light to predetermined directions. 
     In some embodiments, furthermore, the side walls has a convex or a concave structure engaging the first fluorescent layer or the second fluorescent layer. With such arrangement, the first fluorescent layer and the second fluorescent layer may have better reliability on fixing to the substrate. 
     Such convex structure or concave structure provides position limiting effect when materials the fluorescent layers are attached on or into such structures. Particularly, when the fluorescent layers are in gel mode when installed, such fluorescent layer flow and fit the surface of the concave or convex structures, forming a well holding structure. 
     In some embodiment, the first fluorescent layer has a first convex surface on top of the first fluorescent layer, the second fluorescent layer has a second convex surface on top of the second fluorescent layer. 
     In such design, the first convex surface and the second convex surface form lens guiding the first output light and the second output light for mixing the first output light and the second output light. Light paths may be well optimized for different light devices by adjusting the curve ratio, e.g. to form a condensed beam or a diversified light. 
     Except convex surface, in some other embodiments, the first fluorescent layer may have a first concave surface on top of the first fluorescent layer, and the second fluorescent layer has a second concave surface on top of the second fluorescent layer. 
     In some embodiments, the first output light, the second light and the original light not absorbed by the first fluorescent layer and the second fluorescent layer form an overall output spectrum of a white light. 
     Specifically, in some embodiments, the first fluorescent layer and the second fluorescent layer both comprise red phosphor material for generating 640-650 nm output light. In some other embodiments, the first fluorescent layer and the second fluorescent layer both comprise red phosphor material for generating 628-635 nm output light. 
     Please be noted that red, blue or green phosphor refer to phosphor material for emitting red, blue or green light, instead of defining the color of the phosphor materials themselves. 
     In some embodiments, the original spectrum is substantially corresponding to a blue light, the first spectrum is substantially corresponding to a green light, and the second spectrum is substantially corresponding to a red light. 
     In some other embodiments, the original spectrum is substantially corresponding to a ultraviolet light, the first fluorescent layer comprises green phosphor material and blue phosphor material for generating a green light and a blue light, the second fluorescent layer comprises red phosphor material for generating a red light. 
     In some other embodiments, the original spectrum is substantially corresponding to a ultraviolet light, the first fluorescent layer comprises green phosphor material and red phosphor material for generating a green light and a red light, the second fluorescent layer comprises blue phosphor material for generating a blue light. 
     In some embodiments, the first fluorescent layer and the second fluorescent layer have phosphor material, and the phosphor material has larger density near bottom than top in the first fluorescent layer and the second fluorescent layer. This increases better light efficacy because the bottom part of the first and the second fluorescent layers are closer to the light source, thus increasing phosphor excitation efficiency. 
     In some embodiments, the second fluorescent layer has a larger area than the first fluorescent layer. 
     In some embodiments, the second group of LED chips have more LED chips than the first group of LED chips. 
     According to another embodiment of the present invention, a LED device includes a LED module, a first fluorescent layer, and a second fluorescent layer. 
     The LED module includes a plurality of LED components mounted on a substrate for emitting an original light of an original spectrum. 
     The first fluorescent layer surrounds the plurality of LED components for converting the original light to a first output light of a first spectrum. The second fluorescent layer is stacked on the first fluorescent layer for converting the original light not absorbed by the first fluorescent layer and entering the second fluorescent layer to a second output light of a second spectrum. In addition, the second spectrum is partially overlapped with an excitation spectrum of the second fluorescent layer. 
     In some embodiment, the LED device further includes a package housing for holding the substrate and the first fluorescent layer. The substrate has a plurality of electrode pads. The plurality of LED components are attached to the plurality of electrode pads and electrically connected with wires. The electrode pads are connected to an external power source to drive the LED components to emit the original light. 
     In some embodiments, the LED components are LED semiconductor chips mounted on the substrate using chip-on-board packaging. 
     In some other embodiments, the LED component is made with CSP (Chip Scale Package). In addition, the LED device may include a package housing with reflecting walls for reflecting the original light, the first output light, the second output light to predetermined directions. On designing the angle of the reflecting walls, the second output light is prevented to enter the first fluorescent layer to cause energy waste and total output of the second output light. 
     In some other embodiments, the substrate is an elongated strip. Such elongated strip with LED modules may be used for manufacturing various bulbs emulating the shape of traditional bulbs. In addition, when the substrate is transparent, e.g. glass material, the LED device may further have a third fluorescent layer attaching to a backside of the elongated strip for converting the original light passing through the elongated strip to a third output light of the first spectrum, and a fourth fluorescent layer stacked on the third fluorescent layer for converting the original light not absorbed by the third fluorescent layer and entering the fourth fluorescent layer to a fourth output light of the second spectrum. 
     In some other embodiments, the substrate is a flexible circuit board substrate. 
     In some embodiments, the LED device may further have a side wall fixed to the substrate. The side wall has a convex structure or a concave structure engaging the second fluorescent layer. Such convex structure and concave structure may also be used for fixing the first fluorescent layer. This is particularly helpful when the first fluorescent layer and the second fluorescent layer are heated to gel mode during manufacturing. It is difficult to control the surface temperature of the fluorescent layers to be attached together. With such structures, the fluorescent layers are fixed more reliably. 
     In some embodiments, the first fluorescent layer has a first convex surface on top of the first fluorescent layer, the second fluorescent layer has a second convex surface on top of the second fluorescent layer. The first convex surface and the second convex surface may forming one or more lens guiding the first output light and the second output light for mixing the first output light and the second output light. 
     In some other embodiments, the first fluorescent layer has a first concave surface on top of the first fluorescent layer, the second fluorescent layer has a second concave surface on top of the second fluorescent layer. 
     In some embodiments, there is a boundary surface between the first fluorescent layer and the second fluorescent layer, and the boundary surface is a convex surface facing to the LED module. 
     In some other embodiments, the boundary surface between the first fluorescent layer and the second fluorescent layer is a concave surface facing to the LED module. 
     In some embodiments, the first output light, the second light and the original light not absorbed by the first fluorescent layer and the second fluorescent layer form an overall output spectrum of a white light. 
     Furthermore, in some embodiments, the first fluorescent layer and the second fluorescent layer both include red phosphor material for generating 640-650 nm output light. 
     In some other embodiments, the first fluorescent layer and the second fluorescent layer both include red phosphor material for generating 628-635 nm output light. 
     In some embodiments, there is an intermediate part between the first fluorescent layer and the second fluorescent layer. The intermediate part includes mixed materials of the first fluorescent layer and the second fluorescent layer. The thickness of the intermediate part may be less than 10% of the total width of the first fluorescent layer and the second fluorescent layer. The intermediate part has a plurality of micro convex structures between the first fluorescent layer and the second fluorescent layer. Such convex structures may form a plurality of micro optical lens for better distribute light paths. 
     The LED module includes a plurality of LED components mounted on a substrate for emitting an original light of an original spectrum. The first fluorescent layer surrounds the plurality of LED components for converting the original light to a first output light of a first spectrum. The second fluorescent layer is stacked on the first fluorescent layer for converting the original light not absorbed by the first fluorescent layer and entering the second fluorescent layer to generate a second output light of a second spectrum. 
     The second spectrum is partially overlapped with an excitation spectrum of the first fluorescent layer. In addition, there is an intermediate part between the first fluorescent layer and the second fluorescent layer. The intermediate part includes mixed materials of the first fluorescent layer and the second fluorescent layer. The intermediate part has a plurality of micro convex structures between the first fluorescent layer and the second fluorescent layer. 
     In some embodiments, the first fluorescent layer is a dome shape and the second fluorescent layer and the substrate surround the first fluorescent layer. 
     In some embodiments, the LED device further includes a package housing, wherein the package housing and the substrate form a container for storing the first fluorescent layer. 
     In some embodiments, he package housing has a surrounding side wall with larger peripheral size at top than at bottom, e.g. like an inverted pyramid. Such structure further prevents unnecessary waste of the second output light to be emitted into the first fluorescent layer. 
     In some embodiments, the package housing has a surrounding side wall with a reflecting surface facing to the first fluorescent layer. 
     In some embodiments, a heat dissipation material, like powder mixed with metal oxide or metal crystals, may bed mixed in the first fluorescent layer. 
     In some embodiments, the original spectrum is substantially corresponding to a ultraviolet light. The second fluorescent layer contains green phosphor material and blue phosphor material for generating a green light and a blue light, the first fluorescent layer contains red phosphor material for generating a red light. 
     In some embodiments, the LED device may further include a third fluorescent layer containing blue phosphor material for generating blue light spectrum. The second fluorescent layer may contain green phosphor material for generating a green light, and the first fluorescent layer may contain red phosphor material for generating a red light. 
     In some embodiments, the first fluorescent layer may contain red phosphor material and green phosphor material for generating a red light and a green light and the second fluorescent layer may contain blue phosphor material for generating a blue light. 
     According to another embodiment of the present invention, a LED (light emitted diode) device is provided. The LED device has a LED module, a first fluorescent layer, a second fluorescent layer, and a package housing. 
     The LED module is mounted on a substrate for emitting a blue light. 
     The first fluorescent layer has a first side facing to the LED module for converting the blue light to a red light. 
     The second fluorescent layer has a first side attached to a second side of the first fluorescent layer for converting the blue light to a red light emitted from a second side of the second fluorescent layer. 
     The package housing holds the substrate and the first fluorescent layer. 
     With such design, the first fluorescent layer is between the second fluorescent layer and the LED module. In other words, a blue light emitted from the LED module firstly enters the first fluorescent layer, hitting certain phosphor material and generating corresponding red light. In addition, some part of the blue light further moves to the second fluorescent layer to hit other phosphor material to generate green light. With red light and green light, users may see a white light effect. 
     In some embodiments, the LED module has multiple LED chips emitting the blue light. The substrate has a first terminal area and a second terminal area for mounting the multiple LED chips. For example, multiple LED chips are mounted on conductive plates used as the terminal areas with surface mounting device (SMD) technology. 
     The first terminal area and the second terminal area are provided for respectively connected to a positive terminal and a negative terminal of a power source. The first terminal area may have different size as the second terminal area. For example, when there are more LED chips mounted on the first terminal area than on the second terminal area, the first terminal area may have a larger size than the second terminal area to provide better heat dissipation effect. 
     In some embodiments, the first fluorescent has red phosphor material contained in first silicone part, and the second fluorescent layer has green phosphor material contained in a second silicone part. Please be noted that other materials in addition to silica gel, like resin, may be used for containing phosphor powder. 
     In addition, a part of the green light may excite the red phosphor if the green light hits the red phosphor. In other words, if the blue light firstly enters the second fluorescent layer, the blue light may firstly be converted to green light. If such green light continues to move into the first fluorescent layer, part or all of the green light may be consumed and converted into red light. This may decrease the overall green light energy and decreases an overall CRI (color rendering index) of the LED device. 
     Therefore, it is beneficial to place the first fluorescent layer between the second fluorescent layer and the LED module, for improving green light output and deceasing undesired consumption of the green light output. 
     Inventors also find that there the volume ratio of phosphor material in the first fluorescent layer and the second fluorescent layer may be adjusted to further improve different characteristics of the LED device. 
     In some cases, a first volume ratio of the red phosphor to the first silicone part is larger than a second volume ratio of the green phosphor to the second silicone part. 
     In some other cases, a first volume ratio of the red phosphor to the first silicone part is smaller than a second volume ratio of the green phosphor to the second silicone part. 
     The provide different features and characteristics, suitable for making various LED products. 
     In some embodiments, a thickness of the first fluorescent layer is larger than a thickness of the second fluorescent layer. 
     In some other embodiments, a thickness of the first fluorescent layer is smaller than a thickness of the second fluorescent layer. 
     Such variations are found helpful for adjusting product characteristic of the LED device. 
     In addition, the first fluorescent layer may have better heat resisting feature than the second fluorescent layer, when the first fluorescent layer is placed closer to the LED module. In other words, designers may place phosphor material with less heat resisting characteristic as the second fluorescent layer. 
     In some embodiments, the package housing may have a bottom part fixed to the substrate and the package housing has a surrounding wall extended from the bottom part. The wall defines a containing space for holding the first fluorescent layer. 
     For example, the package housing has a hole for holding the substrate and four connecting walls forming a rectangular containing space. The first fluorescent layer and sometimes the second florescent layer are placed in the containing space. 
     There are several ways to design the second fluorescent layer. 
     In some embodiments, a second side of the second fluorescent layer has a curved surface. In other words, the top surface of the second fluorescent layer may have a curve surface. 
     Specifically, an angle of edges of the first side and the second side of the second fluorescent layer would be less than 60 degrees. Such design may increase overall product stability. 
     In some embodiments, the curve surface forms a convex lens, providing better optical characteristic for output light, by directing light to desired direction. 
     In some other embodiments, area of the second side of the second fluorescent layer is smaller than area of the second side of the first fluorescent layer. In other words, when being looked over a top view, a part of the second side of the first fluorescent layer is exposed and uncovered by the second fluorescent layer. 
     In such case, there is an embodiment to place the second fluorescent in the middle place, which causes the second side of second fluorescent layer being surrounded by the second side of the first fluorescent layer from a top view. 
     In some embodiments, the package housing has a ladder wall for engaging with a peripheral part of the second fluorescent layer. In some manufacturing procedures, the first fluorescent layer and the second fluorescent layer are heated as gel mode to be filled into the package holding. When the package holding has a ladder wall, the first fluorescent layer may be filled in a first ladder while the second fluorescent layer may be filled to in a second ladder upper than the first ladder in the ladder wall. 
     In some embodiments, the second side of the second fluorescent layer forms a flat surface. 
     In some other embodiments, the second side of second florescent layer forms a curve surface for different optical characteristic requirement. 
     In some embodiments, the second side of the second fluorescent layer may have multiple convex part corresponding to multiple underlying LED chips of the LED module. It may be implemented by applying gel mode material of the second fluorescent layer to the package for several times respectively to underlying LED chips. Because LED chips usually have certain light emitting angle, it is helpful to maximize the light converting effect by placing more material of the second fluorescent layer on top of corresponding LED chips, particularly when phosphor material is critical cost in LED devices. 
     Please refer to  FIG. 1  to  FIG. 6 , illustrating a LED device embodiment. 
     The LED device has LED chips  1  and a bracket  2  for fixing the LED chips  1 . The LED bracket  2  contains a substrate  21  and four side walls  22  as a package housing. The substrate  21  and the side walls  22  form a containing space  23 . 
     A first terminal area  211  and a second terminal area  212  are disposed on the substrate. The LED chips  1  are placed in the containing space  23  and mounted on surface of the first terminal area  211  and the second terminal area  212 , e.g. via surface mounting device (SMD) technology. The LED chips  1  may be electrically connected in series or in other combination. The first terminal area  211  and the second terminal  212  are further electrically connected to a power source to supply electricity to the LED chips  1 . 
     A first fluorescent layer  31  is disposed for covering the LED chips  1 . A second fluorescent layer  32  is on top of the first fluorescent layer  31 . The wave length of emitted light of the first fluorescent layer  31  is longer than the wave length of emitted light of the second fluorescent layer  32  when a blue light or an ultraviolet light is respectively emitted into the first fluorescent layer  31  and the second fluorescent layer  32 . For example, the first fluorescent layer emits red light when blue light enters the first fluorescent layer  31 , and the second fluorescent layer emits green light when blue light enters the second fluorescent layer  32 . 
     In addition, the first fluorescent layer  31  may be made by mixing red phosphor in a silicone material, and the second fluorescent layer  32  may be made by mixing green phosphor in a silicone material. 
     The LED chips  1  may be LED chips emitting blue light of wavelengths within range 380 nm to 470 nm. The green light emitted from the second fluorescent layer  31  may be within range 500 nm to 560 nm. The red light emitted from the first fluorescent layer  32  may be within 600 nm to 670 nm. 
     Some blue light is not absorbed by either the first fluorescent layer  31  or the second fluorescent layer  32 . Therefore, in some embodiment, the overall output light includes blue light, red light and green light, which together form a white light. 
     With such design, green light is not consumed by red phosphor material and further improves CRI (color rendering index) and overall luminous efficacy. 
     Please be noted that the embodiment is only for explaining the inventive concept, instead of limiting the inventive scope. Other variations may be made by persons of ordinary skilled in the art based on disclosure of this specification. 
     The bracket  2  may be SMD bracket made of PCT material, a mixture of CHDM (1,4-Cyclohexanedimethanol) and DMT (Terephthalic acid dimethyl ester). 
     Please refer to  FIG. 5  and  FIG. 6 . In one embodiment, the first fluorescent layer  31  is disposed in the containing space  23 . The top surface of the second side of the first fluorescent layer  31  is aligned with the top surface of the side walls  22 . 
     The first side of the second fluorescent layer  32  is placed on top of the first fluorescent layer  31 . The size of the second side of the second fluorescent layer  32  is smaller than the size of the second side of the first fluorescent layer  31 . Therefore, part of the first fluorescent layer  31  is exposed and uncovered by the second fluorescent layer  32 . 
     Please refer to  FIG. 7  and  FIG. 8 , which illustrate another way to add the second fluorescent layer. 
     In this embodiment, the first fluorescent layer  31  is placed in the containing space  23 . The top surface of the first fluorescent layer  31  is aligned with the top surface of the side walls  22 . The second fluorescent layer  32  is placed upon the first fluorescent layer  31 . 
     In this embodiment, the second side of the second fluorescent layer  32  has a curve surface. The angle between the first side and the second side of the second fluorescent layer  32  is smaller than 60 degrees. 
     Please refer to  FIG. 9  to  FIG. 12 . 
     In this embodiment, the side walls  22  have a ladder structure  221  for dividing the containing space  23  to a first containing space  231  and a second containing space  232 . 
     The area of the second containing space  232  is larger than the area of the first containing space  231 . The first fluorescent layer  31  is placed in the first containing space  231  and the second fluorescent layer  32  is placed in the second containing space  232 . 
     Please refer to  FIG. 13  and  FIG. 14 , which illustrate experimental results of such design. 
       FIG. 13  illustrate a conventional LED optical characteristic, while  FIG. 14  illustrates optical characteristic of an example of the invention. It is clearly seen that the green light is well improved, which may increase overall CRI and luminous efficacy. Meanwhile, blue light is decreased to protect human eyes. 
     Please refer to  FIG. 15A ,  FIG. 15B  and  FIG. 15C , which illustrate three different way to arrange the fluorescent layers. 
     In  FIG. 15A , a first fluorescent layer  502  surrounds a LED module  503 . A second fluorescent layer  501  is stacked on the first fluorescent layer  502 . A package housing  504  is used for providing a container for the first fluorescent layer  502 . 
     In  FIG. 15B , similar to  FIG. 15A , a LED module  512  is surrounded by a second fluorescent layer  512 . A second fluorescent layer  511  is stacked on the first fluorescent layer  511 . 
     In  FIG. 15C , similar to  FIG. 15B , an additional exposure of the first fluorescent layer  515  is arranged, instead of covering the first fluorescent layer  512  completely. 
     The intermediate surface between the first fluorescent layer  502  and the second fluorescent layer  501  is a convex surface, which may be used as a lens for guiding light to desired direction. For example, to adjust light beam angle, or mixing light of different colors. 
     The top surfaces of the first fluorescent layer and the second fluorescent layer may be concave lens or concave lens, for different optical requirements. 
     Please refer to  FIG. 16A  and  FIG. 16B . 
     In  FIG. 16A , a LED module  614  is surrounded by a first fluorescent layer  612 . A second fluorescent layer  611  is stacked on the first fluorescent layer  612 . A package housing  613  provides a container for storing the first fluorescent layer  612 . 
     In  FIG. 16B , similarly, a LED module  624  is surrounded by a first fluorescent layer  622 . A second fluorescent layer  621  is stacked on the first fluorescent layer  622 . A package housing  623  provides a container for storing the first fluorescent layer  622 . 
     As mentioned before, the curve surface combination may have various configuration to optimize light paths in corresponding light apparatus designs. 
     Please refer to  FIG. 17A  and  FIG. 17B . 
     In  FIG. 17A  and  FIG. 17B , a convex structure  711  and a concave structure  712  are respectively disposed for fixing the top fluorescent layer more reliably. Usually, the fluorescent layers are inserted to the package housing in gel mode after being heated. 
     It is not easy to control cooling timing, while attachment between fluorescent layers depend on status between adjacent fluorescent layers. With such designs, fluorescent layers in gel or liquid mode may fill or hook the concave structure  712  or the convex structure to better fix the fluorescent layers more firmly. 
     Please refer to  FIG. 18 . 
     In  FIG. 18 , an intermediate part  811  exists between a first fluorescent layer  813  and a second fluorescent layer  814 . The intermediate part  811  contains materials of both the first fluorescent layer  813  and the second fluorescent layer  814 . For example, the first fluorescent layer  813  may contain red phosphor and the second fluorescent layer  814  may contain green phosphor. Both red and green phosphor exist in the intermediate part  811 , which makes the overall light transmission better fitting to design needs. 
     In addition, the intermediate surface  813  between the first fluorescent layer  813  and the second fluorescent layer  814  may have a plurality of micro convex structures, serving as micro optical lens for guiding light transmission to better fit design requirements. 
     The thickness of the intermediate part  811  is less than 10% of the total thickness of the first fluorescent layer  813  and the second fluorescent layer  814 . 
     Please refer to  FIG. 19A ,  FIG. 19B  and  FIG. 19C . 
     In  FIG. 19A , a LED device has three fluorescent layers. The first fluorescent layer  913  may contain red phosphor material. The second fluorescent layer  912  may contain green phosphor material and the third fluorescent layer  911  may contain blue phosphor material. 
     In  FIG. 19B , a LED device has a first fluorescent layer  922  containing red phosphor material. The second fluorescent layer  921  may contain both green phosphor and blue phosphor material. 
     In  FIG. 19C , a LED device has a first fluorescent layer  932  containing red phosphor and green phosphor material. The second fluorescent layer  931  contains blue phosphor material. 
     In the embodiments of  FIG. 19A ,  FIG. 19B  and  FIG. 19C , the LED module may be a ultraviolet LED emitting light with frequency between 200 nm to 380 nm. 
     Please refer to  FIG. 20A  and  FIG. 20B . 
     In  FIG. 20A , a LED device has a LED module  751  surrounded by an inverted U shape first fluorescent layer  752  that is further surrounded by a second fluorescent layer  753 . 
     In  FIG. 20B , a LED device has a LED module  761  surrounded by a dome shape first fluorescent layer  762  that is further surrounded by a second fluorescent layer  763 . 
     Please refer to  FIG. 21A , which illustrates a COB LED device, with LED chips  851  covered by a first fluorescent layer  853  and a second fluorescent layer  852 . 
     Please refer to  FIG. 21B , which illustrates a CSP LED device, with a LED die  861  surrounded by a first fluorescent layer  863  and a second fluorescent layer  862 . 
     Please refer to  FIG. 21C , which illustrates another CSP LED device, with a LED die  871  surrounded by a first fluorescent layer  872  and a second fluorescent layer  873 . 
     Please note that the different arrangement and shapes of the fluorescent layers, which teaches persons of ordinary skilled in the art to perform even other variations, which should be still regarded as within the inventive scope. 
     Please refer to  FIG. 22A , which illustrates a LED device with a strip substrate  953  having two surfaces covered by a fluorescent layers  951 ,  952 ,  953  and  954 . 
     Please refer to  FIG. 22B , which illustrates a LED device with a substrates  964  as a flexible circuit board substrate with fluorescent layers  962  and  963  covered thereon. 
     The several embodiments mentioned above may be applied with desired combination of previously mentioned fluorescent layer features. 
     Please refer to  FIG. 23A ,  FIG. 23B  and  FIG. 23C . 
     In addition to stack fluorescent layers, the fluorescent layers may be placed in the same level. 
     In  FIG. 23A , a packaging housing  651  defines two containers  6512  and  6511  for containing two fluorescent layers mentioned above. 
       FIG. 23B  further illustrates that the two containers  6611 ,  6612  may have different size in response to different luminous output of different colors. Corresponding numbers of LED chips may be provided for such design requirement, too. 
       FIG. 23C  show an interleaved arrangement of different color fluorescent layers. Other interleaved patterns may be used. 
     Please refer to  FIG. 24 , which illustrates a LED device having a first fluorescent layer  681  and a second fluorescent layer  682 . A separating component  683  is provided to prevent light from the second fluorescent layer  682  to emit back to the first fluorescent layer  681 . 
     Reflecting surfaces may even be provided to further optimize the overall output. 
     Please refer to  FIG. 25 , which illustrates a LED device with a package side wall  691  having a tilt angle. In such design, light from the top fluorescent layer may have less chance to emit back to the bottom fluorescent layer, causing better luminous efficacy and CRI as mentioned above. 
     Please refer to  FIG. 26 . 
     In  FIG. 26 , another LED device embodiment is illustrated in side view. The LED device has a LED chip  9704  mounted on a metal electrode plate with glue. Wires are also used to connect LED chips, if there are more than, or connect LED chips to electrodes. Red phosphor layer  9703  covers the LED chip  9704  with a curve surface shape. Green phosphor layer  9702  further covers the red phosphor layer  9703  with a curve surface shape. A package housing and the substrate defines a container for storing the red phosphor layer  9703  and the green phosphor layer  9702 . The package housing has a side wall having an angle  9701  between side wall surface to horizontal surface of the substrate. The angle  9701  is adjusted for further preventing green light emitted back to the red phosphor layer  9703 . Preferably, the angle  9701  is between 20 to 70 degrees, or 30 to 60 degrees, e.g. 53 degree. 
     The substrate may have heat conductive metal layer for better transmit heat to outside, increasing reliability of the LED chip  9704 . The package housing may be made of PCT material, PPA or EMC material. The wires may not be necessary for flip chip devices. 
     Please refer to  FIG. 27 . 
     In  FIG. 27 , an LED device has a LED chip  9804  mounted on a substrate. The LED chip is surrounded by a red phosphor layer  9803  that is surrounded and held by an inner wall  9801 . The inner wall prevents green light to enter the red phosphor layer  9803  to waste energy. 
     A green phosphor layer  9802  is surrounded by a package housing sidewall  9807 . The inner wall  9801  may be made of PCT, PPA, EMC or SMD bracket material. In such case, the red phosphor layer  9803  is formed by filling red phosphor into the inner wall  9801 . Alternatively, the red phosphor may be added first, the inner wall  9801  may than be inserted by adding an attaching outer wall with harden glue or other material. 
     With such design, CRI and luminous efficacy are well improved, which is difficult particularly in such crowded technology field. 
     In addition to the above-described embodiments, various modifications may be made, and as long as it is within the spirit of the same invention, the various designs that can be made by those skilled in the art are belong to the scope of the present invention.