Abstract:
An exemplary embodiment of an illumination assembly includes a reflector housing having a plurality of cavities formed therein, an a plurality of light emitters mounted in the plurality of cavities. Each of the plurality of cavities contains a single one of the plurality of light emitters.

Description:
BACKGROUND 
       [0001]    Large display panels such as stadium displays may consist of numerous small light emitting illumination assemblies arranged in an array. A typical illumination assembly consists of one or more light emitters such as LED dies mounted in a plastic housing and having some type of mounting connectors, such as surface mount leads. The LED dies may be mounted in a cavity or reflector cup that directs or focuses light in a desired direction from the illumination assembly. In illumination assemblies having multiple light emitters mounted in a single reflector cup, there may be an irregular far field radiation pattern in the overall light from the light emitters. A light emitter mounted in the center of a reflector cup will reflect uniformly from the sides of the reflector cup. However, light emitters being offset from the center of the reflector cup may not reflect uniformly if they are not positioned symmetrically with respect to the sides of the reflector cup. For illumination assemblies having light emitters of different wavelengths, such as red, green and blue (RGB) LED dies, in a single reflector cup, the light emitted from the illumination assembly may not uniformly have the desired color. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0002]      FIG. 1  is a top perspective view of a prior art illumination assembly having multiple emitters in a single reflector cup. 
           [0003]      FIG. 2  is a top view of a prior art illumination assembly having multiple emitters arranged in a line in a single reflector cup. 
           [0004]      FIG. 3  is a top view of a prior art illumination assembly having multiple emitters arranged nonlinearly in a single reflector cup. 
           [0005]      FIG. 4  is an exemplary plot of the far field radiation patterns in a vertical direction of the prior art illumination assembly of  FIG. 2 . 
           [0006]      FIG. 5  is a top perspective view of an exemplary illumination assembly having multiple emitters in individual reflector cups. 
           [0007]      FIG. 6  is an exemplary plot of the far field radiation patterns in a vertical direction of the illumination assembly of  FIG. 5 . 
           [0008]      FIG. 7  is a top perspective view of an exemplary illumination assembly having multiple emitters with individual lenses. 
           [0009]      FIG. 8  is an exemplary plot of the far field radiation patterns in a vertical direction of the illumination assembly of  FIG. 7 . 
           [0010]      FIG. 9  is a top view of an exemplary illumination assembly having multiple emitters in individual oval reflector cups in a linear arrangement. 
           [0011]      FIG. 10  is a top view of an exemplary illumination assembly having multiple emitters in individual oval reflector cups in a nonlinear arrangement. 
           [0012]      FIG. 11  is a top view of an exemplary illumination assembly having multiple emitters in individual circular reflector cups. 
           [0013]      FIG. 12  is a top view of an exemplary illumination assembly having multiple emitters in individual square reflector cups. 
           [0014]      FIG. 13  is a top view of an exemplary illumination assembly having multiple emitters in individual rectangular reflector cups. 
           [0015]      FIG. 14  is a side cross-sectional view of an exemplary illumination assembly with encapsulant and a lens. 
           [0016]      FIG. 15  is an exemplary display having an array of illumination assemblies with multiple emitters. 
           [0017]      FIG. 16  is a flowchart of an exemplary operation for making an illumination assembly. 
       
    
    
     DESCRIPTION 
       [0018]    The drawings and description, in general, disclose an illumination assembly having multiple emitters and a method of fabricating an illumination assembly having multiple emitters. The illumination assembly has a reflector cup for each of the emitters, thereby closely matching the far field radiation pattern for each of the emitters. The far field radiation pattern may be directed toward the optical axis much more fully and uniformly than with illumination assemblies having multiple emitters located in a single cavity. The viewing angle may be widened or narrowed as desired in all directions away from the optical axis given the additional focusing control provided by placing each light emitter in its own reflector cup, and further by placing a lens adjacent each reflector cup. 
         [0019]    The term “far field” is used herein to refer to a region at a sufficient distance from the illumination assembly that light from the multiple emitters in the illumination assembly has been able to visually merge into a combined color. For example, light emitted from red, green and blue LEDs may visually combine to appear as white to a viewer in the far field. However, this combination may not be uniform if the multiple emitters are not properly reflected by the illumination assembly. The exemplary illumination assembly described herein uniformly reflects light from each of a number of light emitters in the assembly regardless of the physical layout or arrangement of the light emitters. 
         [0020]    Referring now to  FIGS. 1-4 , a prior art illumination assembly  10  will be described in which multiple light emitters  12 ,  14  and  16  are placed in a single reflector cup  20 . The light emitters  12 - 16  may be arranged in a line as illustrated in  FIG. 2  wherein the light emitters  12 - 16  are aligned along a vertical axis  22 . The light emitters  12 - 16  are thus all placed symmetrically in the reflector cup  20  along a horizontal axis  24 , but not along the vertical axis  22 . The far field radiation pattern in the vertical direction for this arrangement is shown in  FIG. 4 . The radiation patterns  26 ,  30  and  32  for the light emitters  12 ,  14  and  16 , respectively are mismatched and skewed across the vertical direction. Light emitters  34 ,  36  and  40  may also have a nonlinear arrangement, such as the triangular arrangement in the single reflector cup  42  of the prior art illumination assembly  44  of  FIG. 3 . The asymmetrical placement of the light emitters  34 - 40  in a single reflector cup  42  will have a similarly mismatched far field radiation pattern as the illumination assembly  10  of  FIGS. 1 and 2 . In a color illumination assembly in which the three light sources are of different colors that combine to form a white light or any other desired color, this mismatched far field radiation pattern skews the perceived color from the display. 
         [0021]    Referring now to  FIGS. 5 and 6 , an illumination assembly  50  having multiple light emitters  52 ,  54  and  56  and improved far field radiation patterns will be described. Each light emitter  52 ,  54  and  56  is placed in its own reflector cup  60 ,  62  and  64 , respectively, enabling the far field radiation pattern from the emitters  52 - 56  to be matched or otherwise tailored as desired. In this exemplary embodiment, the reflector cups  60 - 64  are identically shaped so that the far field radiation patterns  66 ,  70  and  72  are substantially matched in the vertical direction  74  as illustrated in  FIG. 6 . Alternatively, each reflector cup  60 - 64  may be uniquely shaped to tailor the far field radiation patterns as desired. 
         [0022]    The light emitters  52 - 56  and reflector cups  60 - 64  may be numbered, shaped and positioned as desired. For example, in the embodiment illustrated in  FIG. 5 , three light emitters  52 - 56  and associated oval reflector cups  60 - 64  are positioned on a top surface  76  of the illumination assembly  50 , opposite electrical connections  78  on a bottom surface  80  of the illumination assembly  50 . Alternatively, the illumination assembly  50  may emit light from a side surface or end surface, etc as desired. As will also be described in more detail, the shape of the reflector cups  60 - 64  may be altered to shape the far field radiation pattern as desired. In this exemplary embodiment, oval reflector cups  60 - 64  are used to meet hypothetical requirements of a display employing an array of illumination assemblies (e.g.,  50 ), wherein a large viewing angle is needed in a horizontal direction  82 , but a large viewing angle is not needed in the vertical direction  74 . (Note that the terms horizontal and vertical directions are not absolute terms, and that the illumination assemblies may be mounted in a display in any desired orientation.) The long axis of the reflector cups  60 - 64  in the horizontal direction  82  allows light from the light emitters  52 - 56  to spread out over a wide angle, producing a large viewing angle in the horizontal direction  82 . In contrast, by using a narrower axis in the reflector cups  60 - 64  in the vertical direction  74 , the light in the vertical direction  74  is more narrowly directed, producing a narrower viewing angle in the vertical direction  74  and consequently increasing the brightness within that viewing angle. Regardless of the desired viewing angle, the use of an independent reflector cup (e.g.,  60 - 64 ) for each light emitter (e.g.,  52 - 56 ) enables the far field radiation patterns to be matched or otherwise tailored as desired. 
         [0023]    The light emitters  52 - 56  may comprise any suitable light source, such as light emitting diodes, in die form or packaged as desired, laser diodes, fluorescent sources, fiber optic waveguides leading to one or more remote light sources, etc. Any number and color of light emitters may be employed in an illumination assembly. In one exemplary embodiment, a multicolor illumination assembly may be formed by including a red, a green and a blue LED die (e.g.,  52 - 56 ) that visually combine to form a white or other desired overall color output from each individual illumination assembly. Alternatively, an overall white or other desired color light may be formed in a display using multiple monochromatic illumination assemblies. For example, an illumination assembly having one or more red light emitters may be combined with a second illumination assembly having one or more green light emitters and a third illumination assembly having one or more blue light emitters. Each illumination assembly may include a single light emitter, two light emitters, or three light emitters, etc. as desired. 
         [0024]    Referring now to  FIGS. 7 and 8 , an exemplary embodiment will be described in which lenses  84 ,  86  and  90  are placed adjacent each light emitter. For example, each lens  84 - 90  may be placed such that its individual optical axis is aligned to the center of the associated light emitter. The lenses  84 - 90  may have any desired type and shape. For example, the lenses  84 - 90  may be convex, concave, Fresnel lenses, etc or a combination of multiple types and shapes. The lenses  84 - 90  may have the same shape as the underlying reflector cup if desired, such as the oval lenses  84 - 90  illustrated in  FIG. 7  and corresponding with the oval reflector cups  60 - 64  of  FIG. 5 , or may have any other shape. The lenses  84 - 90  may be used to further shape the far field radiation pattern, for example, to a narrower far field radiation pattern  92  ( FIG. 8 ) with greater on-axis brightness than that  94  generated without a lens. 
         [0025]    The lenses  84 - 90  may be individually formed and attached elements, or may be formed as a single unit having multiple lensing regions. The lenses  84 - 90  may be fabricated using any suitable method, such as using a transfer-molding process. The lenses  84 - 90  may also be positioned and mounted adjacent the light emitters using any suitable method, such as by attaching them to the illumination assembly using an adhesive. 
         [0026]    Referring now to  FIGS. 9-13 , a variety of exemplary reflector cup configurations will be described. However, the illumination assembly having multiple emitters is not limited to any of the configurations to be discussed, and may be adapted as needed to produce the desired far field radiation pattern. Emitters (e.g.,  100 ,  102  and  104 ) may be arranged in a line as in the illumination assembly  106  of  FIG. 9 . Alternatively, emitters (e.g.,  110 ,  112  and  114 ) may be arranged nonlinearly as in the triangle formation in the illumination assembly  116  of  FIG. 10 . The reflector cups may have any desired shape to create the needed radiation pattern. For example, reflector cups  120 ,  122  and  124  may have an oval shape as in the illumination assembly  106  of  FIG. 9 . Reflector cups  130 ,  132  and  134  may have a circular shape as in the illumination assembly  136  of  FIG. 11 . Reflector cups  140 ,  142  and  144  may have a square shape as in the illumination assembly  146  of  FIG. 12 . Reflector cups  150 ,  152  and  154  may have a rectangular shape as in the illumination assembly  156  of  FIG. 13 . Reflector cups  160 ,  162  and  164  may also be filled with an encapsulant material  166 ,  170  and  172  such as silicone or epoxy as illustrated in  FIG. 14  to protect light emitters  174 ,  176  and  180  and to improve light extraction efficiency. As described above, lenses  182 ,  184  and  186  may be located above each light emitter  174 - 180  to further shape the radiation pattern. The reflector cups  160 - 164  may be coated with a reflective coating if desired, for example by adding a reflective aluminum coating using a sputter coating process. Any other suitable method and material may be used if desired to increase the reflectivity of the reflector cups  160 - 164 . 
         [0027]    An exemplary display  200  including an array of illumination assemblies (e.g.,  50 ) is illustrated in  FIG. 14 . For example, large stadium displays may be formed by a two dimensional array of illumination assemblies (e.g.,  50 ). The horizontal and vertical viewing angles of the display  200  may be controlled as described above by the shape of the reflector cups and by lenses as needed. The uniformity of the color produced by the display  200  is increased by the use of individual reflective cups for each of the multiple light emitters in each illumination assembly (e.g.,  50 ) as described above. 
         [0028]    An exemplary method of making an illumination assembly is summarized in the flow chart of  FIG. 16 . A reflector housing having a plurality of reflector cups is created  210 , and a light emitter is mounted  212  in each of the plurality of reflector cups. External connectors on the reflector housing, such as surface mount leads or through hole pins are connected  214  to the plurality of light emitters. Optionally, the reflector cups may be coated with a reflective coating, the reflector cups may be filled with an encapsulant material, and lenses may be attached over the reflector cups. 
         [0029]    The illumination assembly having multiple emitters, the display, and the method of making illumination assembly having multiple emitters described herein provide a multicolor light source having well matched far field radiation patterns for uniform colors, as well as controllable viewing angles and high on-axis brightness as allowed by the desired viewing angle. 
         [0030]    While illustrative embodiments have been described in detail herein, it is to be understood that the concepts disclosed herein may be otherwise variously embodied and employed, and that the appended claims are intended to be construed to include such variations, except as limited by the prior art.