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. A light-emitting diode (LED) illumination device, comprising:
 a mounting bracket for attaching the illumination device to a surface;   a swing arm extending from the mounting bracket, a first end of the swing arm engaging the mounting bracket and an opposite second end of the swing arm having an opening for receiving a power cable to power the illumination device;   an end cap rotatably coupled to the second end of the swing arm adjacent to the opening of the swing arm, the end cap and the swing arm cooperating to define a rotational axis, wherein the rotational axis is shared by an axis defined by a route of the power cable, and wherein the end cap has a plurality of teeth disposed a radial distance from the rotational axis and arranged in a semi-circle; and   a hinge element extending from an intermediate location on the swing arm in a position between the first and second ends, a portion of the hinge element engaging the teeth to provide a resistance to secure the illumination device in a rotational position with respect to the mounting bracket around the rotational axis.   
     
     
       16. The illumination device of  claim 15 , wherein the hinge element provides sufficient resistance to secure the illumination device in substantially any rotational position within a 180 degree range of motion. 
     
     
       17. The illumination device of  claim 15 , wherein the hinge element and the end cap form a rack and pinion gear assembly. 
     
     
       18. The illumination device of  claim 15 , wherein the hinge element is a position holding gear. 
     
     
       19. The illumination device of  claim 18 , wherein the hinge element further comprises a torque element that provides a substantially consistent amount of torque to the position holding gear. 
     
     
       20. The illumination device of  claim 19 , wherein the torque element provides the substantially consistent amount of torque to the position holding gear when the position holding gear is stationary. 
     
     
       21. The illumination device of  claim 19 , wherein the torque element provides the substantially consistent amount of torque when the hinge element is rotated. 
     
     
       22. The illumination device of  claim 15 , wherein the hinge element comprises a pivotable, toothed rotatable gear, wherein the teeth on the hinge element engage the teeth on the end cap. 
     
     
       23. The illumination device of  claim 15 , wherein the hinge element further comprises a torque element that facilitates rotational adjustment the illumination device, while still providing the necessary resistance to hold the illumination device in a desired rotational position. 
     
     
       24. The illumination device of  claim 23 , wherein the torque element exhibits a high static energy and a low kinetic energy. 
     
     
       25. The illumination device of  claim 15 , further comprising a strain relief member disposed in the opening to reduce strain applied to the power cable in response to rotational movement about the rotational axis. 
     
     
       26. A light-emitting diode (LED) illumination device, comprising:
 a mounting bracket for attaching the illumination device to a surface;   a swing arm extending from the mounting bracket, a first end of the swing arm engaging the mounting bracket and an opposite second end of the swing arm having an opening for receiving a power cable to power the illumination device;   an end cap rotatably coupled to the second end of the swing arm adjacent to the opening of the swing arm, the end cap and the swing arm cooperating to define a rotational axis, wherein the rotational axis is shared by an axis defined by a route of the power cable, and wherein the end cap has a plurality of teeth arranged radially at distance from the rotational axis;   a pivotable, toothed, hinge element extending from an intermediate location on the swing arm between the first and second ends, wherein the teeth on the hinge element engage the teeth on the end cap to provide a resistance to secure the illumination device in a rotational position with respect to the mounting bracket around the rotational axis;   a housing physically coupled to the end cap; and   a printed circuit board disposed at least partially within the housing, the printed circuit board including a plurality of LEDs.   
     
     
       27. The illumination device of  claim 26 , wherein the plurality of LEDs comprise a plurality of LED arrays disposed on a front surface of the printed circuit board. 
     
     
       28. The illumination device of  claim 27 , wherein each of the plurality of LED arrays comprise a 2×2 LED array. 
     
     
       29. The illumination device of  claim 28 , wherein the 2×2 LED array comprises four LEDs, each having a different output spectrum. 
     
     
       30. The illumination device of  claim 29 , wherein each of the plurality of 2×2 LED arrays is rotated by an angle with respect to a neighboring 2×2 LED array. 
     
     
       31. The illumination device of  claim 28 , wherein each of the 2×2 LED arrays comprise a red LED, a green LED, a blue LED, and a phosphor coated blue LED. 
     
     
       32. The illumination device of  claim 31 , further comprising a dome-shaped optical element disposed on each respective one of the plurality of LED arrays. 
     
     
       33. The illumination device of  claim 32 , wherein each of the LED arrays include a floating louver assembly disposed a distance from the dome-shaped optical element. 
     
     
       34. The illumination device of  claim 26 , wherein the hinge element provides sufficient resistance to secure the illumination device in substantially any rotational position within a 180 degree range of motion. 
     
     
       35. illumination device of  claim 26 , wherein the hinge element further comprises a position holding gear and a torque element that provides a substantially consistent amount of torque to the position holding gear.