Nonhomogeneous Phosphor Layers for LED Angular Color Stability
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Solution Overview
Problem
Large-sized luminophoric particles in light emitting devices are efficient for light conversion but have low light scattering efficiency, leading to high angular variation in Correlated Color Temperature (CCT), which affects the brightness and color consistency of white LEDs.
Innovation Solution
Implementing a layer of luminophoric particles with non-homogeneous sizes, where the equivalent particle diameter decreases with increasing distance from the solid state light emitting source, or using multiple layers with different particle diameters, to enhance light scattering efficiency and reduce angular variation in CCT.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If large-sized luminophoric particles are used, then light conversion efficiency is improved, but light scattering efficiency deteriorates
Solution Approach 1:
The luminophoric layer is segmented into multiple sub-layers, each containing luminophoric particles of different size ranges. This segmentation allows each sub-layer to optimize for specific particle sizes that balance light conversion and scattering efficiencies, resolving the contradiction between large particle benefits (conversion efficiency) and drawbacks (scattering efficiency).
Solution Approach 2:
Different regions of the luminophoric layer (proximal vs. distal sub-layers) are assigned different particle size distributions tailored to their specific functional requirements. The proximal layer uses larger particles for high conversion efficiency near the LED, while the distal layer uses smaller particles for optimal scattering, creating local quality variations that resolve the efficiency-scattering contradiction.
2Use of energy by moving object
If large-sized luminophoric particles are used, then light conversion efficiency is improved, but angular variation in CCT deteriorates
Solution Approach 1:
The luminophoric layer is divided into multiple sub-layers with different particle size distributions, where each sub-layer contributes differently to the overall angular CCT characteristics. This segmentation reduces the angular variation by distributing the optical functions across multiple layers with complementary particle sizes.
Solution Approach 2:
The invention uses a composite structure of multiple luminophoric particle populations with different size ranges within the same layer or across layers. This composite approach combines the advantages of different particle sizes to achieve both high conversion efficiency and stable CCT across viewing angles.
3Reliability
If non-homogeneous particle size distribution is implemented, then light scattering efficiency is improved, but device complexity increases
Solution Approach 1:
The complex particle size distribution is segmented into discrete size ranges assigned to different sub-layers, making the complexity manageable through systematic layering rather than requiring continuous or random size distributions throughout the entire luminophoric layer.
Solution Approach 2:
The invention systematically varies the particle size parameter across different sub-layers, creating a controlled gradient or stepped distribution. This parameter change approach manages complexity by using defined size ranges rather than uncontrolled variations, making the non-homogeneous distribution manufacturable and predictable.
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
This approach increases the brightness of white LEDs while minimizing angular variation in CCT, providing a more consistent and efficient light emission by combining large and small particulate-sized phosphors in distinct layers.
Implementation Method 1
a single blue-emitting LED (e.g., made of indium gallium nitride and/or gallium nitride) may be used in combination with a yellow phosphor, polymer or dye such as for example, cerium-doped yttrium aluminum garnet (which has the chemical formula Y3Al5O12:Ce, and is commonly referred to as 'YAG:Ce'), that 'down-converts' the wavelength of some of the blue light emitted by the LED, changing its color to yellow
Implementation Method 2
Large-sized luminophoric particles in light emitting devices are efficient for light conversion but have low light scattering efficiency
Data Source
AI summary
A light emitting device includes an LED and a layer of luminophoric particles, such as phosphor, that are non-homogeneous in size as a function of distance away from the LED. For example, a first layer of relatively large size phosphor particles may be provided between a second layer of relatively small size phosphor particles and the LED. The large particles can provide high brightness and the small particles can reduce angular color temperature variation in emitted light.