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. A 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 housing;   a plurality of light-emitting diode (LED) arrays;   an emitter board that includes the plurality of LED arrays operatively coupled to and disposed at least partially within the emitter housing;   a plurality of reflectors, each of the plurality of reflectors optically associated with a respective one of the plurality of LED arrays;   a hinge assembly operatively coupled to the emitter housing, the hinge assembly including:
 a semicircular rack operatively coupled to the emitter housing, the semicircular rack having a center of rotation about a central axis; 
 a mounting bracket having an aperture to permit the passage of one or more conductors, the aperture disposed coaxial with the central axis; and 
 a pinion to engage the semicircular rack to cause the semicircular rack to rotate about the central axis, the pinion having a center of rotation about a second axis offset from and parallel to the central axis.  
   
     
     
       16. The illumination device of  claim 15  wherein each of the plurality of LED arrays comprises a plurality of LEDs.  
     
     
       17. The illumination device of  claim 16  wherein each of the plurality of LED arrays includes a two-by-two array that contains four LEDs, wherein the four LEDs include one red LED, one blue LED, one green LED, and one white LED.  
     
     
       18. The illumination device of  claim 17  wherein each of the plurality of LED arrays is rotated at an angle from about 30 degrees to about 120 degrees with respect to at least one neighboring LED array.  
     
     
       19. The illumination device of  claim 15 , further comprising a plurality of optical structures, each of the plurality of optical structures disposed proximate a respective one of the plurality of LED arrays.  
     
     
       20. The illumination device of  claim 19  wherein each of the plurality of optical structures comprises a dome-shaped optical structure that encapsulates the respective LED array and a photodetector associated with the respective LED array such that the photodetector receives at least a portion of the light internally reflected from a surface of the dome-shaped optical structure.  
     
     
       21. The illumination device of  claim 20  wherein each of the plurality of dome-shaped optical structures is disposed proximate the emitter board.  
     
     
       22. The illumination device of  claim 21  wherein each of the plurality of dome-shaped optical structures defines a circular area in a plane of the respective LED array, the circular area having a first diameter, wherein the first diameter is at least 1.5 times to 4 times larger than a largest dimension of the LED array.  
     
     
       23. The illumination device of  claim 22  wherein each of the plurality of dome-shaped optical structures comprises an optical structure formed such that a radius of the dome-shaped structure in the plane of the respective LED array is between 20% and 30% greater than a radius of curvature of the dome-shaped structure.  
     
     
       24. The illumination device of  claim 15  further comprising:
 a power supply board; 
 wherein the emitter board further comprises one or more driver circuits operatively coupled to the power supply board, each of the one or more driver circuits operatively coupled to at least one of the plurality of LED arrays.  
 
     
     
       25. The illumination device of  claim 15  further comprising an exit lens detachably attachable to the emitter housing.  
     
     
       26. The illumination device of  claim 25  wherein the exit lens comprises a light diffusion layer disposed on at least a portion of an internal surface of the exit lens.  
     
     
       27. The illumination device of  claim 26  wherein the exit lens further comprises a plurality of lenslets disposed on at least a portion of an external surface of the exit lens.  
     
     
       28. The illumination device of  claim 27  wherein each of the plurality of lenslets comprises a polygonal, dome-shaped lenslet.  
     
     
       29. The illumination device of  claim 15  wherein the plurality of reflectors comprises a plurality of 60×60-degree reflectors, each forming a 60-degree angle with respect to a plane of the respective LED array.  
     
     
       30. The illumination device of  claim 29  wherein each of the plurality of reflectors further comprises a plurality of louvers having a circular shape with sloping sidewalls operatively coupled to the respective reflector, wherein the sloping sidewalls form a circular area having a first diameter proximate the LED array and a circular area having a second diameter distal from the LED array, the second diameter greater than the first diameter.  
     
     
       31. The illumination device of  claim 30  wherein the sloping sidewalls of the louvers comprise a sidewall forming a 60-degree angle with respect to the plane of the respective LED array.  
     
     
       32. The illumination device of  claim 30  wherein the sloping sidewalls of each of the plurality of louvers include a plurality of planar facets.  
     
     
       33. The illumination device of  claim 15  wherein the plurality of reflectors comprises a plurality of 30×60-degree reflectors.  
     
     
       34. The illumination device of  claim 33  wherein each of the plurality of reflectors further comprises a plurality of louvers having an elliptical shape with sloping sidewalls operatively coupled to the respective reflector, wherein the sloping sidewalls form an elliptical area having a first major axis proximate the LED array and an elliptical area having a second major axis distal from the LED array, the second major axis greater than the first major axis.  
     
     
       35. An illumination device, comprising:
 an emitter housing;   a plurality of light-emitting diode (LED) arrays;   an emitter board that includes the plurality of LED arrays operatively coupled to and disposed at least partially within the emitter housing, each of the plurality of LED arrays rotated in a plane of the LED array an angle of from about 30 degrees to about 120 degrees with respect to at least one neighboring LED array;   a hinge assembly having a first axis of rotation about which the emitter housing rotates, the hinge assembly having a central aperture to permit the passage of at least one conductor therethrough; and   a rack-and-pinion assembly operatively coupled to the hinge assembly, the rack-and-pinion assembly including a curved rack physically coupled to the emitter housing and a rotatable pinion to engage the curved rack, the rotatable pinion having a second axis of rotation that is offset from and parallel to the central axis of rotation.