LED Encapsulant with Inert Particles for Light Extraction and Off-State Color
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Solution Overview
Problem
High power LEDs used in camera flashes emit a yellow-green color when off due to YAG phosphor coatings, which is unattractive and does not match the camera's appearance, and existing encapsulants do not effectively enhance light extraction.
Innovation Solution
Incorporating sub-micron size particles of TiOx or ZrOx into the transparent encapsulant, such as silicone, increases light extraction and changes the off-state color from yellow-green 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 LED appears yellow-green when off, which is unattractive and does not match the camera appearance
Solution Approach 1:
The patent applies composite materials by combining transparent encapsulant material with white pigment particles (such as TiO2, ZnO, or BaSO4) to create a new encapsulant composition. This composite encapsulant maintains the optical transparency needed for white light emission when the LED is on, while the white pigment particles reflect and scatter ambient light when the LED is off, masking the yellow-green phosphor color and making the LED appear white or neutral in the off state.
2Illumination intensity
If transparent encapsulant is used to protect the LED, then light extraction is improved, but further enhancement of light extraction is limited
Solution Approach 1:
The patent changes the optical parameters of the encapsulant by adding white pigment particles with high refractive indices and specific scattering properties. This modifies the light extraction mechanism by introducing additional scattering centers that increase the optical path length and probability of light escaping from the LED, thereby enhancing light extraction efficiency beyond what a plain transparent encapsulant can achieve.
3Object-generated harmful factors
If white pigment particles are added to the encapsulant, then the off-state color becomes white and light extraction is enhanced, but excessive particle concentration may reduce light transmission
Solution Approach 1:
The patent optimizes the concentration parameter of white pigment particles in the encapsulant to achieve the desired balance. By controlling the particle concentration within a specific range, the encapsulant provides sufficient white coloration in the off state while maintaining adequate light transmission and extraction when the LED is on. This parameter optimization prevents excessive scattering that would reduce light transmission.
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 in the encapsulant enhances light output by over 5% and reduces color temperature variation, making the LED appear whiter when off and providing more uniform illumination, suitable for photography 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
Since the inert material (e.g., TiO2 or ZrO2) is white, the appearance of the LED with a YAG phosphor coating appears much whiter when the LED is off
Data Source
AI summary
In one embodiment, sub-micron size granules of TiO2, ZrO2, or other white colored non-phosphor inert granules are mixed with a silicone encapsulant and applied over an LED. 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 in small cameras. 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.