Linear LED illumination device with improved color mixing

Abstract

A linear multi-color LED illumination device that produces uniform color throughout the output light beam without the use of excessively large optics or optical losses is disclosed herein. Embodiments for improving color mixing in the linear illumination device include, but are not limited to, a shallow dome encapsulating a plurality of emission LEDs within an emitter module, a unique arrangement of a plurality of such emitter modules in a linear light form factor, and special reflectors designed to improve color mixing between the plurality of emitter modules. In addition to improved color mixing, the illumination device includes a light detector and optical feedback for maintaining precise and uniform color over time and/or with changes in temperature. The light detector is encapsulated within the shallow dome along with the emission LEDs and is positioned to capture the greatest amount of light reflected by the dome from the LED having the shortest emission wavelength.

What is claimed is: 
     
       1. An illumination device, comprising:
 a plurality of emitter modules spaced apart from each other and arranged in a line, wherein each emitter module comprises an array of at least two different colors of light emitting diodes (LEDs), which are mounted on a substrate and encapsulated within a shallow dome, and wherein a flattened shape of the shallow dome allows a greater portion of light emitted by the array of LEDs to emanate sideways from the emitter module than a hemispherical shaped dome; and 
 a reflector comprising a plurality of louvers, wherein each louver is centered upon and suspended a spaced distance above a different one of the emitter modules to focus a majority of light emitted by that emitter module into an output beam, and wherein each louver is configured to reflect the portion of the light that emanates sideways from adjacent emitter modules to improve color mixing in the output beam. 
 
     
     
       2. The illumination device as recited in  claim 1 , wherein a radius of the shallow dome in a plane of the array of LEDs is 20-30% larger than a radius of a curvature of the shallow dome, so that the portion of the light that emanates sideways from the emitter module exits the shallow dome at small angles relative to a plane of the LED array. 
     
     
       3. The illumination device as recited in  claim 2 , wherein approximately 40% of the light emitted by the array of LEDs exits the shallow dome at approximately 0 to 30 degrees relative to the plane of the LED array. 
     
     
       4. The illumination device as recited in  claim 1 , wherein a top diameter of each louver is substantially larger than a bottom diameter of the louver. 
     
     
       5. The illumination device as recited in  claim 4 , wherein the plurality of louvers each comprise a substantially circular shape with sloping sidewalls. 
     
     
       6. The illumination device as recited in  claim 4 , wherein the plurality of louvers each comprise sidewalls with a substantially parabolic shape. 
     
     
       7. The illumination device as recited in  claim 4 , wherein the louvers are configured to focus the majority of the light emitted by the emitter modules into the output beam by configuring the bottom diameter of the louvers to be substantially larger than a diameter of the emitter modules. 
     
     
       8. The illumination device as recited in  claim 4 , wherein the sloping sidewalls of the louvers include a plurality of planar facets, which are configured to randomize a direction of light reflected from the planar facets. 
     
     
       9. The illumination device as recited in  claim 4 , wherein the louvers are suspended approximately 5 mm to approximately 10 mm above the emitter modules to allow the portion of the light that emanates sideways from the emitter modules to mix underneath the louvers. 
     
     
       10. The illumination device as recited in  claim 1 , wherein the plurality of emitter modules comprise at least a first emitter module, a second emitter module, and a third emitter module, and wherein:
 the second emitter module is spaced equally distant between the first and third emitter modules; 
 the second emitter module is rotated X degrees relative to the first emitter module; 
 the third emitter module is rotated 2X degrees relative to the first emitter module; and 
 wherein X is a rotational angle equal to 360 degrees divided by an integer N, where N is greater than or equal to 3. 
 
     
     
       11. The illumination device as recited in  claim 1 , wherein the array of LEDs comprises at least four LEDs, which are mounted on the substrate close together and arranged in a square pattern near a center of the shallow dome. 
     
     
       12. The illumination device as recited in  claim 11 , wherein the array of LEDs comprises a red LED, a green LED, a blue LED and a white LED. 
     
     
       13. The illumination device as recited in  claim 1 , further comprising:
 an emitter housing, wherein the plurality of emitter modules and the reflector reside within the emitter housing; and 
 an exit lens mounted above the reflector and attached to sidewalls of the emitter housing. 
 
     
     
       14. The illumination device as recited in  claim 13 , wherein an internal surface of the exit lens comprises a flat roughened surface that scatters light rays passing through the exit lens, and wherein an external surface of the exit lens comprises an array of lenslets that randomizes the scattered light rays. 
     
     
       15. An illumination device, comprising:
 an emitter module comprising:
 at least two light emitting diodes (LEDs) mounted on a substrate; and 
 a dome that encapsulates the at least two LEDs; 
 wherein a radius of the dome in a plane of the LEDs is greater than a radius of curvature of the dome; and 
   a reflector comprising a louver that is suspended a distance above the emitter module.   
     
     
       16. The illumination device of claim 15, further comprising a plurality of emitter modules including the emitter module, wherein the plurality of emitter modules are spaced apart from each other and arranged in a line. 
     
     
       17. The illumination device of claim 15, wherein the at least two LEDs comprise a two by two array of LEDs. 
     
     
       18. The illumination device of claim 15, wherein the distance of the louver above the emitter module is within a range of approximately 5 mm to approximately 10 mm. 
     
     
       19. The illumination device of claim 18, wherein the louver comprises sloped sidewalls, and wherein the sloped sidewalls include a plurality of planar facets. 
     
     
       20. The illumination device of claim 15, wherein the radius of the dome in the plane of the LEDs is greater than the radius of curvature of the dome by 20-30%. 
     
     
       21. The illumination device of claim 20, wherein approximately 40% of light emitted by the at least two LEDs exits the dome at approximately 0 to 30 degrees relative to the plane of the LEDs. 
     
     
       22. The illumination device of claim 16, wherein the plurality of emitter modules comprise at least a first emitter module, a second emitter module, and a third emitter module, and wherein:
 the second emitter module is between the first emitter module and third emitter module;   the second emitter module is rotated X degrees relative to the first emitter module;   the third emitter module is rotated 2X degrees relative to the first emitter module; and   X is a rotational angle.   
     
     
       23. The illumination device of claim 15, wherein the louver comprises sloped sidewalls, and wherein the sloped sidewalls include a plurality of planar facets. 
     
     
       24. The illumination device of claim 15, wherein a top diameter of the louver is larger than a bottom diameter of the louver. 
     
     
       25. The illumination device of claim 24, wherein the louver comprises a substantially circular shape. 
     
     
       26. The illumination device of claim 24, wherein the louver comprises a substantially parabolic shape. 
     
     
       27. The illumination device of claim 24, wherein the bottom diameter of the louver is larger than a diameter of the emitter module. 
     
     
       28. The illumination device of claim 24, wherein the louver comprises sloped sidewalls, and wherein the sloped sidewalls include a plurality of planar facets. 
     
     
       29. The illumination device of claim 15, further comprising an exit lens mounted above the reflector, wherein an internal surface of the exit lens comprises a flat roughened surface that scatters light rays passing through the exit lens, and wherein an external surface of the exit lens comprises an array of lenslets that randomizes the scattered light rays. 
     
     
       30. The illumination device of claim 29, further comprising a plurality of emitter modules including the emitter module. 
     
     
       31. The illumination device of claim 30, wherein the plurality of emitter modules are spaced apart from each other and arranged in a line, wherein the plurality of emitter modules comprise at least a first emitter module, a second emitter module, and a third emitter module, and wherein:
 the second emitter module is between the first emitter module and third emitter module;   the second emitter module is rotated X degrees relative to the first emitter module;   the third emitter module is rotated 2X degrees relative to the first emitter module; and   X is a rotational angle.   
     
     
       32. The illumination device of claim 31, wherein the distance of the louver above the emitter module is within a range of approximately 5 mm to approximately 10 mm. 
     
     
       33. The illumination device of claim 32, wherein the radius of the dome in the plane of the LEDs is greater than the radius of curvature of the dome by 20-30%. 
     
     
       34. The illumination device of claim 33, wherein a top diameter of the louver is larger than a bottom diameter of the louver. 
     
     
       35. The illumination device of claim 34, wherein the bottom diameter of the louver is larger than a diameter of the emitter module.