LED module with uniform phosphor illumination
The generally Lambertian LED die emission is modified by an optical structure formed over the LED die that reduces the light emission along a normal axis and enhances the light emission at an angle with respect to the normal axis, producing a certain light emission profile. A phosphor layer is provided overlying the optical structure, such as in a reflective light-mixing chamber. The light emission profile results in more uniform flux from the LED die impinging across the surface of the phosphor. Some of the LED light passes through the phosphor and some of the light is converted to light of a different wavelength. The light emission profile results in more uniform color and temperature across the phosphor. The light emission profile may be created by a lens, a patterned layer over the LED die, a semi-reflective layer over the LED die, an optical sheet, or other technique.
1. A light emitting device comprising:
first light emitting diode (LED) semiconductor layers, the first LED semiconductor layers having a top light emitting surface, the first LED semiconductor layers generating light having a first peak wavelength;
a first wavelength conversion layer overlying and spaced away from the top light emitting surface of the first LED semiconductor layers;
a first optical structure between the first LED semiconductor layers and the wavelength conversion layer and spaced from the wavelength conversion layer by a first gap, the first optical structure reducing a light emission of the first LED semiconductor layers along a normal center axis with respect to the top light emitting surface and enhancing the light emission at an angle with respect to the normal center axis, producing a first light emission profile,
wherein a peak intensity of light emitted from the first optical structure at an angle with respect to the center axis is greater than the peak intensity of light emitted from the first optical structure along the center axis,
wherein the first optical structure is attached to the top light emitting surface and has dimensions limited to an area of the top light emitting surface,
wherein light, having the first light emission profile, generated by the combination of the first LED semiconductor layers and the first optical structure, impinges on the first wavelength conversion layer, and
wherein some of the light passes through the first wavelength conversion layer and some of the light is converted to light of a wavelength different from the first peak wavelength.
2. The light emitting device of claim 1 wherein the first optical structure comprises a semi-reflective layer formed over the first LED semiconductor layers.
3. The light emitting device of claim 2 wherein the semi-reflective layer is a patterned reflective layer.
4. The light emitting device of claim 1 wherein the first optical structure comprises a transparent layer formed over the first LED semiconductor layers, wherein the transparent layer contains features that reflect and refract light from the first LED semiconductor layers to create the first light emission profile.
5. The light emitting device of claim 4 wherein the transparent layer has a conical indentation over a center portion of the LED semiconductor layers.
6. The light emitting device of claim 1 wherein the first optical structure comprises an optical layer, having an optical structure with a pattern, separated from the first LED semiconductor layers by a second gap.
7. The light emitting device of claim 1 further comprising a solid transparent layer between the first LED semiconductor layers and the first optical structure.
8. The light emitting device of claim 1 further comprising a reflective light-mixing chamber containing the first LED semiconductor layers, first optical structure, and first wavelength conversion layer, wherein the light-mixing chamber comprises a reflective base and at least one reflective side wall.
9. The light emitting device of claim 1 wherein the first wavelength conversion layer is a substantially flat layer.
10. The light emitting device of claim 1 wherein the first wavelength conversion layer comprises a phosphor layer.
11. The light emitting device of claim 1 further comprising:
at least second LED semiconductor layers;
a second optical structure overlying the second LED semiconductor layers; and
a reflective light-mixing chamber containing the first LED semiconductor layers, first optical structure, first wavelength conversion layer, second LED semiconductor layers, and second optical structure, wherein the light-mixing chamber comprises a reflective base and at least one reflective side wall,
for mixing the light from the first LED semiconductor layers and the second LED semiconductor layers, wherein the second optical structure improves uniformity of light impinging across the first wavelength conversion layer.
12. The light emitting device of claim 11 wherein the first wavelength conversion layer overlies both the first LED semiconductor layers and the second LED semiconductor layers.
13. The light emitting device of claim 11 wherein the second LED semiconductor layers generate light having a second peak wavelength different from the first peak wavelength.
14. The light emitting device of claim 11 wherein the first optical structure and the second optical structure are portions of a single sheet.
15. The light emitting device of claim 11 wherein the second optical structure is substantially identical to the first optical structure so that the second LED semiconductor layers in combination with the second optical structure produces a second light emission profile substantially identical to the first light emission profile, wherein the light having the first light emission profile and the light having the second light emission profile are mixed in the chamber.