Scattering Layer for LED Color Uniformity
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Solution Overview
Problem
Existing light source assemblies, particularly those using solid state lighting (SSL) devices with wavelength converters, face challenges in achieving uniform white light emission due to variations in color over position and angle, which affect color temperature and overall light quality.
Innovation Solution
A light source assembly is developed with a scattering layer applied to the wavelength converting element's light emitting surface, where the backscattering strength varies between 10% to 50%, reducing color variations by scattering light back into the element, thereby improving color uniformity and allowing for a thinner wavelength converting element without compromising conversion performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a wavelength converting element is used with an SSL device, then white light is generated, but color variations occur over position and angle
Solution Approach 1:
The patent applies a scattering layer with spatially varying properties to different regions of the wavelength converting element. The scattering layer has different scattering coefficients in different zones, allowing localized correction of color variations that occur at different positions on the LED surface. This enables each region to be optimized for its specific color characteristics.
Solution Approach 2:
The scattering layer acts as an intermediary between the wavelength converting element and the external environment. It mediates the light output by scattering photons back into the converting element, increasing the path length and probability of wavelength conversion, thereby reducing color variations without affecting the fundamental white light generation mechanism.
2Loss of substance
If the wavelength converting element is made thinner, then material costs are reduced, but conversion performance decreases
Solution Approach 1:
The scattering layer enables continuous wavelength conversion by scattering unconverted photons back into the wavelength converting element multiple times. This increases the effective path length and number of conversion opportunities, allowing thinner converting elements to achieve the same conversion performance as thicker ones would provide without the scattering layer.
Solution Approach 2:
The scattering layer creates periodic interaction between photons and the wavelength converting material through multiple scattering events. Light that passes through the thin converting element without conversion is scattered back for another opportunity to convert, creating repeated conversion cycles that compensate for the reduced thickness.
3Manufacturing precision
If color correction techniques are applied, then color uniformity improves, but device complexity increases
Solution Approach 1:
The scattering layer is integrated directly onto the surface of the wavelength converting element, merging the color correction function with the light conversion component. This eliminates the need for separate correction mechanisms or multiple discrete components, reducing overall device complexity while achieving color uniformity.
Solution Approach 2:
The scattering layer serves multiple functions simultaneously: it increases the effective path length for wavelength conversion, corrects color variations over position and angle, and can be applied as a thin coating that does not significantly increase device size. This multi-functionality reduces the need for additional dedicated components.
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 scattering layer enhances color uniformity in both near and far fields, making the light source more suitable for high-end applications, reduces material costs, and allows for customization and optimization of color correction, effectively addressing color variation issues in SSL devices.
Implementation Method 1
a scattering layer applied to a light emitting surface of the wavelength converting element. The scattering layer is adapted to scatter light back through the light emitting surface into the wavelength converting element
Implementation Method 2
adapted to convert some of the received light to a different wavelength
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A light source assembly (1, 11, 13) comprising: a solid state lighting device (3); a wavelength converting element (4) arranged to receive light emitted by the solid state lighting device (3) and adapted to convert some of the received light to a different wavelength; and a scattering layer (7, 12, 14) applied to a light emitting surface (6) of the wavelength converting element (4). The scattering layer (7, 12, 14) is adapted to scatter light back to the wavelength converting element (4), and a backscattering strength of the scattering layer (7, 12, 14) varies over said light emitting surface (6) so as to reduce variations in the color of the light emitted from the light emitting surface (6).