Light-Emitting Device with Localized Phosphor and White Reflector
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Solution Overview
Problem
Existing light-emitting devices with phosphor layers suffer from color unevenness and thermal issues due to large contact areas between the phosphor and light-reflecting members, leading to reliability and brightness problems.
Innovation Solution
A light-emitting device design featuring face-down mounted elements with a phosphor-containing film on a transparent plate covered by a low-melting-point glass layer, where the region above gaps between elements is not covered with phosphor, and a white reflector surrounds the elements and glass layer to enhance light extraction and reduce thermal expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a phosphor layer is provided to cover the light-emitting element and light-reflecting member, then luminance is improved through light reflection, but color unevenness occurs due to different emission chromaticity in regions directly above the light-reflecting member
Solution Approach 1:
The phosphor layer is selectively positioned to cover only the light-emitting element while leaving the light-reflecting member uncovered. This local differentiation ensures that regions with different light sources (LED vs reflected light) maintain their appropriate chromaticity characteristics, eliminating color unevenness while preserving luminance enhancement from the reflector.
2Illumination intensity
If the phosphor layer has large contact area with the light-reflecting member, then light extraction is improved, but thermal expansion and heat deterioration of the light-reflecting member occur due to heat from the phosphor layer
Solution Approach 1:
The phosphor layer is extracted from the region directly above the light-reflecting member, creating a clear separation between the phosphor-containing area and the reflector. This eliminates direct thermal contact between the heat-generating phosphor and the light-reflecting member, preventing thermal expansion and heat deterioration while maintaining effective light extraction in the phosphor-covered regions.
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 design achieves high reliability, brightness, and color evenness by minimizing phosphor layer thickness, reducing thermal stress, and improving light extraction efficiency.
Implementation Method 1
the contact area between the phosphor layer and the light-reflecting member is large and the thermal expansion or heat deterioration of the light-reflecting member is likely to occur due to heat released from the phosphor layer
Implementation Method 2
light emitted from the region has a large proportion of fluorescence and chromaticity is different from that in light emitted from other regions
Implementation Method 3
light laterally emitted from the light-emitting element is reflected by the light-reflecting member so as to improve luminance
Data Source
AI summary
A light-emitting device includes a plurality of light-emitting elements face-down mounted on a substrate, a plurality of structures each including a transparent plate, a phosphor-containing film provided on a lower surface of the transparent plate and a transparent covering layer provided on the lower surface of the transparent plate so as to cover lower and side surfaces of the phosphor-containing film, the structures being each provided on each of the plurality of light-emitting elements such that a lower surface of the transparent covering layer contacts a top surface of the plurality of light-emitting elements, and a white reflector to cover a side surface of the plurality of light-emitting elements and a side surfaces of the transparent covering layer. At least a portion of a region directly above a gap between the plurality of light-emitting elements is not covered with the phosphor-containing film.