LED Encapsulant with Inert Particles for Light Extraction
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Solution Overview
Problem
High power LEDs used in camera flashes have a yellow-green off-state color due to YAG phosphor coatings, which is unattractive and not aesthetically compatible with camera appearances, and existing methods do not effectively enhance light extraction beyond current levels.
Innovation Solution
Incorporating sub-micron size particles of TiO2 or ZrO2 into the transparent encapsulant, such as silicone, which increases light extraction and changes the off-state color to white, improving brightness and color temperature uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If YAG phosphor coating is applied to the LED, then white light is emitted when the LED is on, but the off-state color becomes yellow-green which is unattractive
Solution Approach 1:
The patent applies composite materials by combining the transparent encapsulant with dispersed inert particles (TiO2, ZrO2, or other white pigments) to create a composite encapsulant material. This composite structure allows the encapsulant to perform multiple functions: maintaining optical transparency when the LED is on, and providing a white appearance when the LED is off, thereby eliminating the yellow-green color issue while preserving white light emission during operation.
2Illumination intensity
If inert particles are added to the encapsulant, then light extraction is increased and brightness is enhanced, but transmission through the encapsulant is reduced at higher percentages
Solution Approach 1:
The patent applies parameter changes by optimizing the concentration of inert particles in the encapsulant to a specific range (0.1% to 10% by weight, preferably 1% to 5%). At these optimized concentrations, the encapsulant achieves maximum light extraction enhancement and brightness improvement while maintaining adequate light transmission. This parameter optimization resolves the contradiction by finding the sweet spot where the beneficial scattering effect enhances extraction without excessive absorption or blocking of light.
3Loss of energy
If the encapsulant is made more transparent, then light transmission is improved, but the off-state color remains yellow-green
Solution Approach 1:
The patent resolves this contradiction by creating a composite encapsulant that combines the base transparent material (silicone or epoxy) with dispersed inert white pigment particles. The transparent base material ensures high light transmission when the LED is on, while the suspended inert particles provide a white appearance when the LED is off. The composite structure allows both properties to coexist: transparency for light transmission and white pigment dispersion for aesthetic off-state appearance.
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 addition of TiO2 or ZrO2 particles enhances light output by up to 6% and significantly reduces color temperature variation across the emission angle, making the LED appear whiter when off and more uniformly illuminated when on, improving photography and projection applications.
Implementation Method 1
granules of TiOx, ZrOx, or other white non-phosphor inert material are mixed with the substantially transparent encapsulant for LEDs... sub-micron size particles of the inert material, such as TiO2, in the encapsulant increase the brightness (lumens) of a GaN LED
Implementation Method 2
GaN LED dies that emit blue light covered by a layer of yttrium aluminum oxide garnet (YAG) phosphor that emits a yellow-green light when energized by the blue light
Implementation Method 3
A semiconductor LED, such as a GaN LED, has an index of refraction (e.g., n=2.2-3.0 for GaN) that is much higher than that of air (n=about 1). By encapsulating the LED in a transparent material, such as silicone (n=1.4-1.76), having an intermediate index of refraction, the light extraction is significantly increased.
Data Source
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AI summary
In one embodiment, sub-micron size granules (34) of TiO 2, ZrO 2, or other white colored non-phosphor inert granules are mixed with a silicone encapsulant (32) and applied over an LED (10). In one experiment, the granules increased the light output of a GaN LED more than 5% when the inert material was between about 2.5-5% by weight of the encapsulant. Generally, a percentage of the inert material greater than 5% begins to reduce the light output. If the LED has a yellowish YAG phosphor coating, the white granules in the encapsulant make the LED appear whiter when the LED is in an off state, which is a more pleasing color when the LED is used as a white light flash (42) in small cameras (40). The addition of the granules also reduces the variation of color temperature over the view angle and position over the LED, which is important for a camera flash and projection applications.