Abstract:
A lighting apparatus is described. One embodiment of the lighting apparatus includes a substrate and a lighting element. The lighting element is coupled to the substrate to emit light through a light exit plane. The light exit plane is substantially perpendicular to the substrate. By providing a lighting device with a substrate oriented perpendicular to the light exit plane of the lighting device, the lighting device can enable better mixing of the light from different LEDs. The lighting apparatus facilitates light mixing, generally, to minimize or eliminate dark spots on the diffusion panel. The lighting device also facilitates color mixing to produce relatively consistent white light on the diffusion panel.

Description:
BACKGROUND OF THE INVENTION 
   Most liquid crystal display (LCD) panels use backlighting to provide a bright image to the viewer. Backlighting is typically provided by diffusing white light from a fluorescent light source or several light emitting diode (LED) sources. To provide evenly distributed backlighting, LCD panels have a diffusion panel that receives the light along one edge of the panel and diffuses the light throughout the face of the diffusion panel. The white light may be directly generated by the fluorescent light source or the LEDs. However, colored LEDs emitting such colors as red, green, and blue (RGB) are also used in some applications. Where colored LEDs are used, the different colors are mixed to create the white light. 
   In applications that use LEDs, several LEDs typically are mounted on a single substrate. The LEDs and substrate are referred to as an LED device. One type of LED device is referred to as an LED array. Some LED arrays have individual lenses for each of the LEDs. Other LED arrays have multiple LEDs encapsulated together between reflector walls. Whether the LEDs have individual lenses or are encapsulated together, conventional LED devices cause dark spots, or zones, on an adjacent diffusion panel. For example, the LED devices with individual lenses may have dark spots between adjacent LEDs. LED devices with several LEDs encapsulated together may have dark spots between adjacent LED devices. 
   In view of this, what is needed is an LED device to provide a better light distribution to overcome the problems of dark spots on the diffusion panel. 
   SUMMARY OF THE INVENTION 
   A lighting apparatus is described. One embodiment of the lighting apparatus includes a substrate and a lighting element. The lighting element is coupled to the substrate to emit light through a light exit plane. The light exit plane is substantially perpendicular to the substrate. By providing a lighting device with a substrate oriented perpendicular to the light exit plane of the lighting device, the lighting device can enable better mixing of the light from different LEDs. 
   In one embodiment, the lighting apparatus facilitates light mixing, generally, to minimize or eliminate dark spots on the diffusion panel. In another embodiment, the lighting device facilitates color mixing to produce relatively consistent white light on the diffusion panel. The quality of light mixing results, at least in part, from to the increased path length of a substantial portion of the emitted light emitted, in contrast to LED devices that directly emit light. The path length refers to the distance from the LED chip to the exit surface of the lighting apparatus. Although embodiments of the lighting apparatus may directly emit some light rays, the light rays that impinge on the reflector surface have a relatively long path length. The longer path length allows for greater overlap of rays from different colored LEDs mounted on the same substrate. 
   A method for transmitting light into a light guide is also described. One embodiment of the method includes providing a lighting device with a substrate substantially perpendicular to a light exit plane, emitting light in a direction substantially parallel to the light exit plane, and reflecting the light off of a reflective surface to redirect the light toward the light exit plane. Other embodiments of the method also may include propagating the light through the light exit plane and a transmission interface into a light guide, propagating the light through an optical lens between the lighting device and the transmission interface of the light guide, propagating the light through a plurality of encapsulants within the lighting device, or propagating the light through a phosphor encapsulant. 
   A method for making a lighting device is also described. One embodiment of the method includes providing a light emitting diode (LED) chip coupled to a substrate, encapsulating the LED chip on the substrate with a first encapsulant, and providing a reflector to reflect the light from the LED chip to a light exit plane perpendicular to the substrate. Another embodiment of the method also includes providing a second encapsulant between the first encapsulant and the reflector, coupling a thermal coupler to the substrate to transfer heat away from the substrate, or coupling a heat sink to the thermal coupler to transfer the heat away from the thermal coupler and the substrate. 
   Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrated by way of example of the principles of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  depicts a conventional light system which uses LED devices having LEDs encapsulated in a common encapsulant. 
       FIG. 2  depicts a conventional light system which uses LED devices having individual LED lenses. 
       FIG. 3  depicts one embodiment of an indirect LED device for illuminating a light guide. 
       FIG. 4  depicts a cross-section of one embodiment of an indirect LED device. 
       FIG. 5  depicts another cross-section of the indirect LED device of  FIG. 4 . 
       FIG. 6  depicts a cross-section of another embodiment of an indirect LED device to facilitate heat dissipation. 
       FIG. 7A  depicts a production stage of one embodiment of an indirect LED device. 
       FIG. 7B  depicts the production stage of  FIG. 7A  using another embodiment of an indirect LED device. 
       FIG. 7C  depicts the production stage of  FIG. 7A  using another embodiment of an indirect LED device. 
       FIG. 8  depicts another production stage of the indirect LED device of  FIG. 7A . 
       FIG. 9  depicts another production stage of the indirect LED device of  FIG. 7A . 
       FIG. 10  depicts another production stage of the indirect LED device of  FIG. 7A . 
       FIG. 11  depicts an alternative embodiment of an indirect LED device. 
       FIG. 12A  depicts another embodiment of an indirect LED device. 
       FIG. 12B  depicts exemplary light ray paths using the re-entrant reflector block of the indirect LED device of  FIG. 12A . 
       FIG. 13  depicts another embodiment of an indirect LED device having an optical lens. 
       FIG. 14  depicts another embodiment of an indirect LED device having a phosphor lens. 
       FIG. 15  depicts another embodiment of an indirect LED device to illustrate heat dissipation from the indirect LED device. 
       FIG. 16  is a process flow diagram of an indirect lighting method which may be used in conjunction with an indirect LED device. 
       FIG. 17  is a process flow diagram of a manufacturing method which may be used to manufacture an indirect LED device. 
   

   Throughout the description, similar reference numbers may be used to identify similar elements. 
   DETAILED DESCRIPTION 
     FIG. 1  depicts a conventional light system  10  which uses LED devices  15  having LEDs encapsulated in a common encapsulant. Each LED device  15  has reflector walls, or sidewalls (i.e., the structural walls separating the LED dice, or chips, on adjacent LED devices), at both ends of the LED device. The separation distance between LEDs of adjacent LED devices is called pitch  20 . The pitch  20  between the LED devices  15  at least partially determines the light pattern within the light guide plate  25 . One example of a light guide plate  25  is a diffusion panel such as may be used in a liquid crystal display (LCD) panel. 
   The use of LED devices  15  with sidewalls to illuminate a light guide plate  25  results in dark spots  30  on the light guide plate  25 . The dark spots  30  are due to the pitch  20  of the sidewalls of the LED devices  15  because the sidewalls block and prevent the light from mixing and passing through the transmission interface  35  (i.e., the edge through which the light enters) of the light guide plate  25 . Where colored LEDs are used to produce white light, color variations also are visible by the user because the individual colors do not adequately mix with other colors. Ideally, the diffusion panel  25  would evenly diffuse the light from the LEDs throughout the surface of the diffusion panel  25  to provide an evenly distributed, white backlight for an LCD panel. However, the dark spots  30  and/or color variations resulting from the pitch  20  of the LED devices  15  may be visible to the user. 
     FIG. 2  depicts a conventional light system  40  which uses LED devices  15  having individual LED lenses. LED devices  15  using an LED array  45  of LEDs with individual lenses can also cause dark spots  30  in the light guide plate  25 . In particular, the dark spots  30  may appear between the individual LEDs. To reduce the appearance of dark spots  30  on an LCD panel, the LCD panel may be oversized so that the dark spots  30  are within a “black out” area not visible to the viewer. However, oversizing the LCD panel increases the cost and size of the LCD panel. Alternatively, the effective area of the LCD panel may be reduced, but reducing the effective area of the LCD panel would result in non-standard display ratios (i.e., display ratios other than 4:3, 16:9, etc.). Other conventional LCD panels address the issue by increasing the distance between the diffusion panel  25  and the LEDs, thus allowing the light to mix before propagating into the light guide plate  25 . However, increasing the mounting distance in this manner also increases the cost and size of the LCD panel. 
     FIG. 3  depicts one embodiment of an indirect LED device  100  for illuminating a light guide. The illustrated LED device  100  includes a substrate  102  and several LED chips  104  (also referred to as LEDs or LED dice) mounted to the substrate  102 . In one embodiment, the substrate  102  is a metal-coated plastic substrate. Other exemplary substrates  102  include a rigid printed circuit board (PCB), a flexible PCB, a metal core PCB, and a taped leadframe. However, the substrate  102  may be another type of substrate in other embodiments. The LEDs  104  may include one or more types of LEDs. In one embodiment, the LEDs  104  include red, green, and blue (RGB) LEDs. In another embodiment, the LEDs  104  may include white, cyan or other colors of LEDs. In another embodiment, the LEDs  104  may include “blue-converted” white LEDs (e.g., blue LEDs in combination with a phosphor resin). In another embodiment, the LEDs  104  may generate other colors by partially converting the LED light emissions from a lower to a higher wavelength to form a resulting combination of unconverted and converted light. Exemplary colors rendered by the combination of unconverted and converted light include cyan, green, yellow, orange, pink, and other colors. Furthermore, the LEDs  104  may be top-emitting LEDs or another type of LEDs. 
   In one embodiment, a reflector block  106  is mounted to the substrate  102 . The reflector block  106  may be made from an aluminum core or another material that conducts heat. In another embodiment, the reflector block  106  may be fabricated from other materials. For example, the reflector block  106  may be plastic such as polycarbonate (PC), liquid crystal polymer (LCP), or another plastic material. The outer shape of the reflector block may be rectangular, curvilinear, polygonal, or another shape. 
   The reflector block  106  includes a reflector surface  108  which, when oriented relative to the LEDs  104 , reflects light from the LEDs  104  toward an aperture to exit the LED device  100 . More details of how light potentially travels within and exits the LED device  100  are shown and described with reference to  FIGS. 4 and 5 . The contour of the reflector surface  108  may be linear, curvilinear, angular, or another geometry. In one embodiment, the contour of the reflector surface  108  is approximately parabolic, with a portion next to the substrate  102  being approximately perpendicular to the substrate  102 . This same portion may be approximately parallel to the light exit plane, which is also substantially perpendicular to the substrate  102 . (One example of a light exit plane is shown and described in more detail with reference to  FIGS. 4 and 5 .) In another embodiment, the contour of the reflector surface  108  facilitates propagation of approximately parallel light rays from the LED device  100 . Alternatively, the contour of the reflector surface  108  may facilitate diffusion of the light in one or more directions. 
   The reflector surface  108  may be implemented by applying a reflective coating to the reflector block  106 , or may be a finished surface of the reflector block  106  itself. In certain embodiments, the reflector surface  108  may affect the reflected light in various ways. For example, the reflector surface  108  may include a diffusant or may be finished in such a way to scatter the reflected light in multiple directions. In another embodiment, the reflector surface  108  may include a layer or coating of phosphor/resin mix to generate a “blue-converted” white light. 
   The illustrated LED device  100  also includes an encapsulant  110  to protect the LEDs  104  on the substrate  102 . One exemplary encapsulant  110  is silicone, although other translucent substances may be used to encapsulate the LEDs  104 . The encapsulant  110  (or multiple encapsulants  110 ) is generally used to fill the space between the substrate  102 , including the LEDs  104 , and the reflector block  106 . In one embodiment, the encapsulant  110  may contain diffusant particles to scatter the light from the LEDs  104 . Exemplary diffusant particles include nano-particles, silica, titania, and quartz, although other diffusant particles may be used. In another embodiment, the encapsulant  110  may include phosphor to generate “blue-converted” white light, which may be used exclusively or in combination with other colors of LEDs  104 . 
     FIG. 4  depicts a cross-section of one embodiment of an indirect LED device  100 . The LED device  100  is located adjacent to and oriented to propagate light into a light guide  120 . As an example, the LED  104  emits a light ray toward the reflector surface  108 , which reflects the light ray toward the light guide  120 . In this way, the light ray indirectly propagates (i.e., the light ray is reflected) into the light guide  120 . Indirectly reflecting the light from the LED  104  to the light guide  102  may have certain advantages compared to conventional lighting devices. For example, embodiments of the indirect LED device  100  provide better color mixing of different colors of lights. Other embodiments may reduce the profile of the aperture (e.g., the surface area of the encapsulant  110  through which the light propagates between the substrate  102  and the reflector block  106 ) of the LED device  100 . For example, in one embodiment, the profile of the aperture may be approximately three millimeters. Other embodiments which implement indirect reflection may reduce the cost of fabrication compared to conventional lighting devices. In another embodiment, the indirect LED device  100  may provide improved light collimation (i.e., the viewing angle) out of the aperture, as well as maximize light coupling efficiency to the light guide  120 . 
     FIG. 5  depicts another cross-section of the indirect LED device  100  of  FIG. 4 . The illustrated LED device  100  depicts how light from the LED  104  may propagate into the light guide  120  in a substantially parallel manner. In particular, the reflector surface  108  may have a contour to reflect the light so that the light travels substantially parallel to the substrate  102 , which is perpendicular to the light exit plane  124  (represented by the dashed line). The light exit plane  124  is the plane through which the light propagates as it exits the LED device  100 . In one embodiment, the light exit plane  124  may be substantially parallel to the transmission interface  122  of the light guide  120 . 
     FIG. 6  depicts a cross-section of another embodiment of an indirect LED device  130  to facilitate heat dissipation. The illustrated LED device  130  includes a substrate  102 , an LED  104 , and a reflector block  106 , as described above, although shown in a slightly different configuration. The LED device  130  also includes a heat sink  132  coupled to the substrate  102 . In one embodiment, the heat sink  132  conducts heat from the substrate  102  and dissipates the heat through convection or through conduction to another material. For example, the heat sink  132  may conduct heat to a metal plate, LCD packaging, or another heat dissipation material. Similarly, the reflector block  106  may be made of a material such as aluminum to facilitate heat dissipation. By dissipating heat from the LED device  130 , the life of the LED  104  and LED device  130  may be extended compared to conventional lighting devices. In another embodiment, the LED device  130  may be more efficient than conventional lighting devices. Although the heat sink  132  is shown coupled directly to the substrate  102 , other embodiments, of the LED device  130  may include interceding thermal pads, adhesives, or plates to conductively couple the substrate  102  to the heat sink  132 . Furthermore, the heat sink  132  (and/or thermal pads) may be at least partially wrapped around (i.e., on multiple sides) the exterior of the LED device  130 . Another example and additional description of heat dissipation are described below with reference to  FIG. 15 . 
     FIG. 7A  depicts a production stage of one embodiment of an indirect LED device  100 . In this production stage, the LED  104  is mounted to the substrate  102 . A bonding wire  142  is provided to bond the LED  104  to the substrate  102 . In one embodiment, the substrate  102  may be approximately three millimeters in length (from top to bottom as shown in  FIG. 7A ), although other sizes of substrates may be implemented. Alternatively, other production methods may be used to suit the type of LED  104  that is used. For example,  FIG. 7B  depicts the production stage of  FIG. 7A  using another embodiment of an indirect LED device  100 , namely, a 2-wire InGaN LED  104  on a sapphire substrate  102 . As another example,  FIG. 7C  depicts the production stage of  FIG. 7A  using another embodiment of an indirect LED device  100 , namely, a flip-chip LED  104 . 
     FIG. 8  depicts another production stage of the indirect LED device  100  of  FIG. 7A . In this production stage, a first encapsulant  144  is used to encapsulate the LED  104  and the bonding wire  142  on the substrate  102 . The first encapsulant  144  may include a phosphor, a diffusant, or another filler. Alternatively, the first encapsulant  144  may be free of fillers. 
     FIG. 9  depicts another production stage of the indirect LED device  100  of  FIG. 7A . In this production stage, the reflector block  106  is coupled to the substrate  102 . Although the reflector block  106  is shown coupled to the substrate  102  in a particular configuration, other configurations may be implemented. In one embodiment, the reflector block  106  is adhered to the substrate. The reflector surface  108  is oriented with respect to the LED  104  so that light from the LED  104  is reflected toward the light exit plane  124  of the LED device  100 . 
     FIG. 10  depicts another production stage of the indirect LED device  100  of  FIG. 7A . In this production stage, a second encapsulant  146  is disposed within the remaining space between the substrate  102  and the reflector block  106 . In one embodiment, the second encapsulant  146  encapsulates the first encapsulant  144  on the substrate  102 . The second encapsulant  146  may include no fillers or may include a phosphor, a diffusant, or another filler. 
   Although  FIGS. 7A-10  depict one example of how an LED device  100  may be manufactured, other manufacturing operations may be performed in addition to or instead of the production stages shown and described above. In particular, the operations implemented to manufacture an LED device  100  may be tailored to accommodate certain processes, materials, or other manufacturing considerations. 
     FIG. 11  depicts an alternative embodiment of an indirect LED device  150 . The illustrated LED device  150  includes a substrate  102  and an LED  104  mounted to the substrate  102 . The substrate  102  is substantially perpendicular to the light exit plane  124 . The reflector block  152  is also coupled to the substrate  102  and includes a reflector surface  154  that is curvilinear, but not necessarily parabolic. In another embodiment, the reflector surface  154  may be linear. 
     FIG. 12A  depicts another embodiment of an indirect LED device  160 . The illustrated LED device  160  includes a substrate  102  and an LED  104  mounted to the substrate  102 . The substrate  102  is substantially perpendicular to the light exit plane  124 . The reflector block  162  is also coupled to the substrate  102  and includes a reflector surface  164 . The reflector surface  164  is curvilinear and has a concave shape with a profile of a re-entrant curve. The LED device  160  has a lens formed from a first encapsulant  144 . In another embodiment, the LED device  160  also may include a second encapsulant  146 .  FIG. 12B  depicts exemplary light ray paths using the re-entrant reflector block  162  of the indirect LED device  160  of  FIG. 12A . In particular, some of the light rays impinge on the reflector surface  164  at several locations, while other light rays impinge at a single location, and other light rays propagate directly to the light exit plane  124 . The light rays that reflect multiple times may provide additional light mixing compared to the light rays that are reflected only once. 
     FIG. 13  depicts another embodiment of an indirect LED device  170  having an optical lens  172 . The optical lens  172  facilitates directing the light in a predetermined light distribution pattern as it propagates through the light exit plane  174  and out of the LED device  170 . The optical lens  172  also may be referred to as a micro lens. In one embodiment, the optical lens  172  is integrated with the second encapsulant  146 . In another embodiment, the optical lens  172  may be separate from, but coupled to, the second encapsulant  146 . Alternatively, the optical lens  170  may be coupled to the reflector block  106 , the substrate  102 , the light guide  120  (not shown), or another component of the lighting system. 
     FIG. 14  depicts another embodiment of an indirect LED device  180  having a phosphor lens  182 . The phosphor lens  182  may facilitate generating a “blue-converted” white light from a blue LED  104 . In one embodiment, the phosphor lens is coupled between the substrate  102  and the reflector surface  186  of the reflector block  184 . Alternatively, the phosphor lens  182  may be coupled to the LED device  180  at the reflector block  184 , the substrate  102 , or another component of the LED device  180 . 
     FIG. 15  depicts another embodiment of an indirect LED device  190  to illustrate heat dissipation from the indirect LED device  190 . The illustrated LED device  190  includes a substrate  192  and an LED  104  coupled to the substrate  192 . A first encapsulant  144  encapsulates the LED  104  on the substrate  192 . A reflector block  106  with a reflector surface  108  is coupled to a flexible and bendable substrate  192 , which wraps around an end of the reflector block  106 . In the absence of a second encapsulant  146 , an air gap exists between first encapsulant  144  and the reflector block  106 , although other embodiments may include a second encapsulant  146 . 
   In one embodiment, the flexible substrate  192  includes a top thermally and electrically conducting layer  193  (also referred to as a top electrode layer), an insulative middle core layer  194 , and a bottom thermally conducting layer  195 . The top electrode layer  193  provides the LED chip  104  with an electrical connection to one or more external terminals (not shown). One or more thermal vias  196  provide for heat dissipation from the top thermally conducting layer  193  through the middle core layer  194  to the bottom thermally conducting layer  195 . In one embodiment, a heat sink  197  is coupled to the exposed surface of the bottom thermally conducting layer  195  to facilitate heat dissipation. Heat is conducted away from the LED chip  104  through the top thermally conducting layer  193 , the thermal vias  196 , and the bottom thermally conducting layer  195 . A second top electrode layer  198  provides a second electrical connection to one or more external terminals (not shown) for the LED chip  104 . In one embodiment, the top layer  193 , the bottom layer  195 , and the second electrode layer  198  are copper (Cu), the middle core layer  194  is a polyimide material, and the thermal vias  196  are blind vias. Other embodiments of the LED device  190  may include other materials, as well as other structural variations. 
     FIG. 16  is a process flow diagram of an indirect lighting method  200  which may be used in conjunction with an indirect LED device  100 . At block  202 , an LED device  100  is provided. The LED device  100  includes a substrate  102  that is substantially perpendicular to the light exit plane  124  of the LED device  100 . At block  204 , the LED  104  emits light in a direction substantially parallel to the light exit plane  124 . In one embodiment, the LED  104  is a top-emitting LED to emit light away from and perpendicular to the substrate  102 . At block  206 , the reflective surface  108  reflects the light and redirects the light toward the light exit plane  124  of the LED device  100 . At block  208 , the light propagates through a transmission interface  122  of a light guide  120  and into the light guide  120 . 
     FIG. 17  is a process flow diagram of a manufacturing method  220  which may be used to manufacture an indirect LED device  100 . At block  222 , an LED chip  104  coupled to a substrate  102  is provided. At block  224 , the LED chip  104  is encapsulated on the substrate  102  with a first encapsulant  144 . At block  226 , a reflector  106  is provided to reflect light from the LED chip  104  to a light exit plane  124  which is perpendicular to the substrate  102 . The reflector  106  includes a reflector surface  108  to reflect the light. At block  228 , a second encapsulant  146  is provided between the first encapsulant  144  and the reflector  106 . 
   Although the operations of the method(s) herein are shown and described in a particular order, the order of the operations of each method may be altered so that certain operations may be performed in an inverse order or so that certain operations may be performed, at least in part, concurrently with other operations. In another embodiment, instructions or sub-operations of distinct operations may be implemented in an intermittent and/or alternating manner. 
   Although specific embodiments of the invention have been described and illustrated, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated. The scope of the invention is to be defined by the claims appended hereto and their equivalents.