Wavelength-Converted LED With Non-Uniform Phosphor Thickness
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Solution Overview
Problem
Conventional light-emitting devices with wavelength converting materials suffer from color nonuniformity due to varying mixing ratios of primary and secondary light across the light extraction surface, especially at the edge and inner regions, leading to differences in light intensity and color across the emitting surface.
Innovation Solution
A light-emitting device configuration where the luminance of primary light emitted from the edge portion is set higher than that from the inner region, with a primary light intensity distribution control mechanism ensuring a uniform mixing ratio of primary and secondary light across the wavelength converting portion, achieved through specific semiconductor layer designs and electrode configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the wavelength converting portion is formed uniformly over the LED chip, then the light path length becomes uniform, but color nonuniformity still occurs due to differences in primary light intensity between edge and inner regions
Solution Approach 1:
The patent applies local quality by making the wavelength converting portion thicker at the edge portion compared to the inner region. This non-uniform thickness distribution compensates for the lower primary light intensity at the edges, ensuring that the product of light intensity and path length (which determines secondary light intensity) is uniform across the entire light extraction surface, thereby eliminating color nonuniformity.
Solution Approach 2:
The patent changes the physical parameter of the wavelength converting portion's thickness to solve the color nonuniformity problem. By increasing the thickness at the edge portion where primary light intensity is lower, the optical path length is extended to compensate for the reduced light intensity, thereby achieving uniform secondary light emission across different regions.
2Illumination intensity
If the edge portion of the wavelength converting portion is made thicker, then color nonuniformity is reduced, but the overall device thickness increases
Solution Approach 1:
The patent applies local quality by making the wavelength converting portion thicker at the edge portion compared to the inner region. This non-uniform thickness distribution compensates for the lower primary light intensity at the edges, ensuring that the product of light intensity and path length (which determines secondary light intensity) is uniform across the entire light extraction surface, thereby eliminating color nonuniformity.
3Illumination intensity
If inorganic fluorescent material particles are used, then scattering action occurs to suppress light color difference, but manufacturing complexity increases
Solution Approach 1:
The patent changes the physical parameter of the wavelength converting portion's thickness to solve the color nonuniformity problem. By increasing the thickness at the edge portion where primary light intensity is lower, the optical path length is extended to compensate for the reduced light intensity, thereby achieving uniform secondary light emission across different 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
This configuration eliminates color nonuniformity by ensuring uniform light emission across the light extraction surface, achieving consistent color irradiation on the irradiation surface while maintaining a thin LED form factor.
Implementation Method 1
a wavelength converting portion that includes a wavelength converting material that absorbs part of the primary light and emits secondary light
Implementation Method 2
a light-emitting element that is disposed on the base and that emits primary light
Data Source
Figure 1~2(b)
Figure 3(a)~3(c)
Figure 4(a)~4(b)
AI summary
A light-emitting device 1 includes a base 2 and a light-emitting element 3 that is disposed on the base 2. The light-emitting element 3 is made up of a plurality of semiconductor layers including a light-emitting layer, and at the same time, is covered with a wavelength converting portion 4 that includes a wavelength converting material. The light-emitting layer emits primary light, and the wavelength converting material absorbs part of the primary light and emits secondary light. The luminance of the primary light emitted from the edge portion of the light extraction surface of the light-emitting device 3 is higher than the luminance of the primary light emitted from the inner region located inside the edge portion, and the ratio of the primary light and the secondary light that are emitted from a light extraction surface 6 of the wavelength converting portion 4 is substantially uniform across the light extraction surface 6 of the wavelength converting portion 4. Thereby, a light color difference across the light extraction surface of the wavelength converting portion that covers the light-emitting element can be reduced further, and it is possible to irradiate an irradiation surface with light of uniform color.