Emitter module for an LED illumination device
An illumination device comprises one or more emitter modules having improved thermal and electrical characteristics. According to one embodiment, each emitter module comprises a plurality of light emitting diodes (LEDs) configured for producing illumination for the illumination device, one or more photodetectors configured for detecting the illumination produced by the plurality of LEDs, a substrate upon which the plurality of LEDs and the one or more photodetectors are mounted, wherein the substrate is configured to provide a relatively high thermal impedance in the lateral direction, and a relatively low thermal impedance in the vertical direction, and a primary optics structure coupled to the substrate for encapsulating the plurality of LEDs and the one or more photodetectors within the primary optics structure.
1. An illumination device comprising:
a substrate having an upper surface and a lower surface transversely opposed across a thickness of the substrate from the upper surface,
wherein the substrate includes one or more materials having a transverse thermal conductivity measured across the thickness of the substrate and an in-plane thermal conductivity measured orthogonal to the transverse thermal conductivity, and
wherein the transverse thermal conductivity is greater than the in-plane thermal conductivity;
a plurality of light-emitting diodes (LEDs) disposed on the upper surface of the substrate;
a plurality of photodetectors disposed on the upper surface of the substrate,
a heat sink disposed proximate at least a portion of the lower surface of the substrate, at least a portion of the heat sink transversely opposed across the thickness of the substrate from the plurality of LEDs and the plurality of photodetectors; and
control circuitry to periodically:
reduce a drive current provided to each of the plurality of LEDs to a non-operative level;
apply a non-operative drive current to at least some of the plurality of photodetectors;
determine a forward voltage across each of the plurality of LEDs, and
determine a drive current for each of the plurality of LEDs to provide at least one of: a defined chromaticity or a defined luminous output.
2. The illumination device of claim 1 wherein the substrate comprises a plurality of vias through a layer of the substrate having the in-plane conductivity, each of the plurality of vias filled with a thermally conductive material having the transverse thermal conductivity.
3. The illumination device of claim 2 wherein each of at least some of the plurality of vias are disposed proximate one of the plurality of LEDs.
4. The illumination device of claim 2 wherein each of at least some of the plurality of vias is disposed proximate one of the plurality of photodetectors.
5. The illumination device of claim 1 further comprising:
a primary optics structure at least partially encapsulating at least a portion of the plurality of LEDs.
6. The illumination device of claim 5 wherein the primary optics structure at least partially encapsulates at least a portion of the plurality of photodetectors.
7. The illumination device of claim 5 wherein the primary optics structure comprises a dome-shaped structure.
8. The illumination device of claim 5 , wherein the plurality of LEDs comprises at least four LEDs, which are mounted on the upper surface of the substrate close together and arranged in an array near a center of the primary optics structure.
9. The illumination device of claim 1 , wherein the plurality of LEDs comprises a red LED, a green LED, a blue LED, and a white or yellow LED.
10. The illumination device of claim 9 , wherein the plurality of photodetectors comprises one or more of a red LED, an orange LED, or a yellow LED.
11. The illumination device of claim 1 , wherein the plurality of LEDs comprises a chain of red LEDs, a chain of green LEDs, a chain of blue LEDs, and a chain of white or yellow LEDs, and wherein each chain comprises two to four LEDs of a same color.
12. The illumination device of claim 11 , wherein the plurality of photodetectors comprises one or more red LEDs and one or more green LEDs.
13. The illumination device of claim 1 , wherein a thickness of the heat sink ranges between about 1 mm and about 10 mm.
14. The illumination device of claim 1 , wherein the heat sink is formed from a material having a thermal conductivity that ranges between about 200 W/(mK) and about 400 W/(mK).
15. The illumination device of claim 1 , wherein the heat sink is formed from a copper, copper-alloy, aluminum, or aluminum alloy material.
16. The illumination device of claim 1 , further comprising:
memory circuitry to store a data structure that includes LED emitter forward voltage data, LED chromaticity data, and LED luminous flux data as a function of photodetector forward voltage.
17. The illumination device of claim 16 wherein to determine a forward voltage across each of the plurality of LEDs, the control circuitry to further:
determine a forward voltage across each of the plurality of LEDs using the measured photodetector forward voltage and the stored data structure.