Broadband dielectric reflectors for LED
A broadband, omnidirectional, multi-layer, dielectric reflector for an LED in a white light emitting device provides both near 100% reflectivity across the visible spectrum of light, and electrical insulation between the substrate and the electrical circuitry used to power and control the LED. When a sealant material, having a higher index of refraction than air, is used to protect the LED and the accompanying electrical circuitry, an aluminum reflector layer or substrate is provided to make up for the loss of reflectivity at certain angles of incidence.
1. A light emitting diode (LED) device comprising:
an LED for emitting light at a first wavelength;
a substrate comprising a layer of reflective metallic material having a coefficient of thermal conductivity greater than 200 W/mK to increase heat dissipation from the LED;
electrical circuitry for providing power to the LED from external sources disposed in between the substrate and the LED;
a wavelength conversion material covering the LED for converting light emitted at the first wavelength to light of at least a second wavelength, which combined with the light of the first wavelength forms a broadband light source; and
a multi-layer dielectric structure of alternating high and low index material layers in between the substrate and the electrical circuitry providing both electrical insulation for the electrical circuitry's connections and reflectivity for the broadband light source, wherein the multi-layer dielectric structure is between 2 μm and 20 μm thick, and
wherein the layer of reflective metallic material and the multi-layer dielectric structure provide over 95% average reflectivity for light at wavelengths between 400 nm and 680 nm over an angle of incidence range of 0° to 90°.
2. The device according to claim 1 , wherein the multi-layer dielectric structure is a broadband reflector reflecting at least 95% of light over a range of 400 nm to 680 nm.
3. The device according to claim 1 , wherein the first and second wavelengths combine to form white light.
4. The device according to claim 1 , wherein the wavelength conversion material comprises a plurality of different materials for converting the light emitted at the first wavelength to light at second and third wavelengths, which combine with the first wavelength to form white light.
5. The device according to claim 1 , wherein the multi-layer dielectric structure comprises a plurality of sections, each section for reflecting a different bandwidth, defined by a center wavelength, of from 75 nm to 125 nm each, each section comprising a plurality of alternating high and low index layers, each layer having an optical width approximately a quarter of the center wavelength.
6. The device according to claim 1 , wherein the multi-layer dielectric structure comprises a plurality of pairs of high and low index material layers, each pair for reflecting a different bandwidth of from 5 nm to 15 nm, defined by a center wavelength, each layer having an optical width approximately a quarter of the center wavelength.
7. The device according to claim 1 , further comprising a sealant material in which the wavelength conversion material is dispersed; wherein the sealant material is transparent to the first and second wavelengths of light.
8. The device according to claim 7 , wherein the transparent sealant material comprises one or more materials selected from the group consisting of silicone, epoxy, glass, plastic, and polymer.
9. The device according to claim 1 , wherein the substrate comprises a reflective metallic material.
10. The device according to claim 1 , wherein the substrate comprises aluminum.
11. The device according to claim 1 , wherein the multi-layer dielectric structure is between 3 μm and 8 μm thick.