Curved Light Extraction Block for OLED Panels
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Solution Overview
Problem
Current OLED lighting panels suffer from low light extraction efficiency due to waveguiding losses, with existing light extraction techniques like Shiang and D'Andrade not optimizing geometry for maximum efficiency or spreading light away from the surface normal, and being less effective for large area light sources.
Innovation Solution
The use of a light extraction block with a three-dimensional, substantially curved surface, featuring a radius of curvature greater than the maximum height of the block, and index matching with the OLED panel to enhance light extraction and spread illumination away from the surface normal, utilizing materials like glass, acrylic, or high refractive index plastics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a traditional hemispherical light extraction block is used, then light extraction efficiency is improved, but the volume required is large and it is less effective for large area light sources
Solution Approach 1:
The patent applies spheroidality by using a curved surface (hemispherical or portion of hemispherical) on the light extraction block. This curved geometry optimizes light extraction by reducing total internal reflection at the interface, allowing more light to escape from the OLED stack. The curvature is specifically designed with a radius of curvature greater than the maximum height of the block, creating an optimized optical path for light extraction.
Solution Approach 2:
The patent transitions from a traditional hemispherical design to a planar or substantially planar light extraction block with a curved surface. This dimensional change maintains the beneficial light extraction properties of curvature while reducing the overall volume requirement. The curved surface is applied to a flattened geometry, optimizing light extraction for large area sources without requiring the full hemispherical volume.
2Illumination intensity
If sharply angled sides with reflective coating are used (Shiang design), then light is directed towards the front surface, but light extraction efficiency is not optimized and illumination away from surface normal is not enhanced
Solution Approach 1:
The patent replaces sharply angled planar surfaces with a curved surface (hemispherical or portion thereof). This curved geometry naturally directs light rays at optimized angles for extraction, eliminating the need for complex reflective coatings and sharp angles. The curvature provides inherent optical guidance that enhances light extraction efficiency without adding geometric complexity.
3Loss of energy
If a truncated square-pyramid luminaire is used (D'Andrade design), then light extraction is enhanced, but emission intensity and color are not uniform with viewing angle and strong color shift occurs
Solution Approach 1:
The patent uses a curved surface (hemispherical or portion of hemispherical) instead of a truncated pyramid geometry. This curved surface provides more uniform light extraction across different viewing angles by creating consistent optical paths. The curvature distributes light extraction more evenly, reducing the color shift and intensity variations that occur with angular viewing in pyramidal designs.
Solution Approach 2:
The patent achieves homogeneous light extraction properties across the surface by using a curved geometry with consistent radius of curvature. This homogeneity ensures uniform emission intensity and color characteristics with viewing angle, eliminating the strong color shifts associated with non-uniform pyramidal structures.
4Ease of manufacture
If a planar light extraction block is used, then manufacturing is simpler, but light extraction efficiency is limited due to waveguiding losses
Solution Approach 1:
The patent combines the simplicity of a planar block with the optical benefits of a curved surface. The light extraction block maintains a substantially planar overall shape for ease of manufacturing, but incorporates a curved surface (hemispherical or portion thereof) at the light-emitting interface. This hybrid approach provides improved light extraction efficiency through curvature while maintaining manufacturing simplicity through the planar form factor.
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 significantly improves light extraction efficiency for large area OLED light sources, achieving greater than 90% light extraction efficacy compared to traditional hemispherical designs, while maintaining uniform emission intensity and minimizing color shift with viewing angle.
Implementation Method 1
The only outcoupled modes are those with angle to the surface normal less than the critical angle θC, where θC=sin−1(nair/norg)≈36° for norg=1.7. Substrate modes are emitted through the edges of the substrate
Implementation Method 2
A light extraction block may be optically connected to the OLED substrate emissive surface... the at least one three-dimensional light emitting surface includes a substantially curved surface
Data Source
AI summary
Light extraction blocks, and OLED lighting panels using light extraction blocks, are described, in which the light extraction blocks include various curved shapes that provide improved light extraction properties compared to parallel emissive surface, and a thinner form factor and better light extraction than a hemisphere. Lighting systems described herein may include a light source with an OLED panel. A light extraction block with a three-dimensional light emitting surface may be optically coupled to the light source. The three-dimensional light emitting surface of the block may includes a substantially curved surface, with further characteristics related to the curvature of the surface at given points. A first radius of curvature corresponding to a maximum principal curvature k1 at a point p on the substantially curved surface may be greater than a maximum height of the light extraction block. A maximum height of the light extraction block may be less than 50% of a maximum width of the light extraction block. Surfaces with cross sections made up of line segments and inflection points may also be fit to approximated curves for calculating the radius of curvature.