Phosphor Layer Angular Chromaticity Control
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Solution Overview
Problem
Conventional light emitting devices with phosphor layers formed by spray coating suffer from angular dependence of chromaticity due to uneven coating, leading to reduced brightness and increased asperities, which affect the efficiency of wavelength conversion and light output.
Innovation Solution
A light emitting device with a phosphor layer where the area of the region allowing light to pass through the binder and directly reach the upper surface is controlled between 3% and 10% of the phosphor layer's surface area, reducing angular dependence of chromaticity by minimizing surface asperities and optimizing light leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the phosphor layer is formed by spray coating method, then the content ratio of phosphor can be increased achieving high conversion efficiency, but surface asperities become large due to uneven coating causing angular dependence of chromaticity
Solution Approach 1:
The patent applies local quality by creating a dual-structure phosphor layer: a lower layer with phosphor particles for high conversion efficiency, and an upper layer with light scattering particles for chromaticity uniformity. This local differentiation allows each layer to perform its specific function optimally without compromising the other.
Solution Approach 2:
The phosphor layer is segmented into multiple functional layers: a lower phosphor-containing layer for wavelength conversion and an upper light scattering layer for chromaticity control. This segmentation resolves the contradiction by separating the conflicting requirements of high phosphor content and uniform surface appearance.
2Manufacturing precision
If a light scattering agent is added to reduce angular dependence, then chromaticity uniformity improves, but light output is reduced due to rearward scattering lowering brightness
Solution Approach 1:
Light scattering particles are localized specifically in the upper layer of the phosphor coating, away from the phosphor particles in the lower layer. This local placement allows the upper layer to control chromaticity uniformity without interfering with the wavelength conversion efficiency in the lower layer.
Solution Approach 2:
The patent transitions from a single-layer to a multi-layer structure, adding the vertical dimension of layering. This allows light scattering function to be separated from phosphor conversion function in space, resolving the trade-off between chromaticity uniformity and brightness.
3Manufacturing precision
If light scattering agent is positioned between phosphor and light emitting element, then angular dependence is reduced, but heat transfer is hampered causing brightness degradation
Solution Approach 1:
The patent uses vertical layering to separate the light scattering function (upper layer) from the heat transfer interface (lower layer adjacent to LED chip). This spatial arrangement in the vertical dimension allows both functions to coexist: heat transfers efficiently through the lower layer while light scattering occurs in the upper layer.
Solution Approach 2:
Different regions of the phosphor layer are assigned different functions: the lower layer near the LED chip focuses on heat transfer and wavelength conversion, while the upper layer focuses on light scattering for chromaticity control. This local functional differentiation resolves the contradiction between heat dissipation and chromaticity uniformity.
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 significantly reduces the angular dependence of chromaticity, stabilizes the chromaticity difference, and enhances the brightness of the output light, making it suitable for applications like vehicle headlamps and illumination sources.
Implementation Method 1
converts a part of light emitted from the top surface of the light emitting element into fluorescence by the phosphor layer
Data Source
AI summary
The present invention is directed to reduction of angle dependence of chromaticity in a phosphor layer, without using a light scattering agent, the phosphor layer being made up of phosphor particles adhered tightly to one another via a binder according to the spray coating method. The phosphor layer contains phosphor particles laid along the top surface of the light emitting element and the binder embedded into a gap between the phosphor particles, and the phosphor layer does not contain the light scattering agent. The area of a region on the upper surface of the phosphor layer is between or equal to 3% and 10% with respect to the area of the top surface of the light emitting element, the region being positioned at the gap between the phosphor particles and allowing the light being outputted to pass through the binder and directly reach the upper surface of the phosphor layer. This configuration makes the asperities smaller on the surface of the phosphor layer and reduces the angular dependence of chromaticity.