LED Light Extraction via Refractive Index Gradients
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Solution Overview
Problem
Light emitting diodes (LEDs) suffer from reduced external quantum efficiency due to total internal reflection and Fresnel losses, as photons are refracted and reflected within the device rather than escaping, leading to a significant loss of light output.
Innovation Solution
The implementation of light enhancement features such as reflectors, shaping, and texturing on the exterior surfaces of LEDs to maximize the probability of photons exiting the device in desired directions, including lenticular surfaces, beveled cuts, and random roughening, which help redirect trapped light and enhance light output efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If light is emitted from the active region through multiple layers with different refractive indexes, then light generation occurs in all directions, but total internal reflection causes significant loss of light output
Solution Approach 1:
The patent applies parameter changes by modifying the refractive index profile through multiple dielectric layers with varying refractive indexes (n1, n2, n3) to control light propagation angles and reduce total internal reflection losses at interfaces
Solution Approach 2:
The patent introduces intermediary dielectric layers between the active region and external environment to mediate light transmission, using layers with progressively changing refractive indexes to facilitate gradual light extraction and reduce reflection losses
2Ease of operation
If light crosses an interface from higher to lower refractive index medium, then light bends away from normal, but at angles greater than critical angle total internal reflection occurs
Solution Approach 1:
The patent changes the refractive index parameters of successive dielectric layers to create a gradient that modifies the critical angle conditions, allowing light to escape at wider angular ranges by reducing the refractive index step discontinuities
Solution Approach 2:
The patent adds dimensional complexity by introducing multiple intermediate layers between the high-index active region and low-index external medium, creating a stepped transition that expands the angular acceptance cone for light extraction
3Illumination intensity
If there is a difference in refractive indexes between two materials at an interface, then Fresnel reflection occurs, but this reduces the percentage of light emitted to air
Solution Approach 1:
The patent systematically changes the refractive index parameter across multiple interfaces by using dielectric layers with progressively varying indexes, thereby reducing the magnitude of Fresnel reflection at each interface through smaller index steps
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The use of these light enhancement features significantly increases the external quantum efficiency of LEDs by reducing internal reflections and enhancing light output, resulting in improved light transmission and emission efficiency.
Implementation Method 1
a certain percentage will be totally internally reflected, never escape the diode
Implementation Method 2
Snell's law dictates that the photons will be refracted as they pass from one material to the next
Implementation Method 3
One of the exterior surfaces has a light enhancement feature selected from the group consisting of a reflector, shaping, and texturing
Data Source
AI summary
A light emitting diode is disclosed that includes an active region and a plurality of exterior surfaces. A light enhancement feature is present on at least portions of one of the exterior surfaces of the diode, with the light enhancement feature being selected from the group consisting of shaping and texturing. A light enhancement feature is present on at least portions of each of the other exterior surfaces of the diode, with these light enhancement features being selected from the group consisting of shaping, texturing, and reflectors.