Front-lit semi-retro-reflective display with convex protrusions
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Solution Overview
Problem
Conventional front-lit, semi-retro-reflective displays suffer from inefficient light reflection, with about half of the light being lost due to Lambertian reflectance, limiting perceived brightness and requiring improved luminance to exitance ratios for broader adoption.
Innovation Solution
A front-lit display with a transparent, selectively emissive light directionality system that uses a directional front light and a semi-retro-reflective electronic paper surface with convex protrusions and light extractor elements to redirect light in a perpendicular direction, maintaining a non-Lambertian output and enhancing luminance to exitance ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional Lambertian reflection is used in front-lit displays, then the display structure is simple and easy to manufacture, but about 50% of the light is reflected away from the viewer, limiting perceived brightness and luminance to exitance ratio
Solution Approach 1:
The patent applies spherical microlenses (convex protrusions) on the front surface of the display to redirect reflected light. These curved optical elements focus and redirect light rays that would otherwise be scattered in Lambertian reflection, concentrating them back toward the viewer's direction and improving perceived brightness while reducing light loss.
Solution Approach 2:
The patent changes the optical parameters of the front surface by introducing microlenses with specific curvature radii and spacing. This transforms the reflection pattern from Lambertian (diffuse) to a more directional pattern, altering the light distribution parameters to favor viewer-direction reflection and improve luminance to exitance ratio.
2Illumination intensity
If conventional Lambertian reflection is used, then manufacturing is simpler, but the luminance to exitance ratio is limited to approximately 1/p
Solution Approach 1:
The patent introduces spherical microlenses on the front surface to control light reflection direction. These curved optical structures redirect reflected light preferentially toward the viewer, increasing the luminance to exitance ratio from 1/p to approximately 2/p, while maintaining a relatively simple overall display structure.
Solution Approach 2:
The front surface is segmented into multiple discrete microlenses (convex protrusions) rather than being a continuous flat surface. This segmentation allows each microlens to independently control light reflection in its local area, collectively achieving improved directional reflection across the entire display surface.
3Ease of operation
If light is radiated equally in all directions (Lambertian), then the light distribution is uniform, but a large portion of reflected light is not reflected back to the viewer
Solution Approach 1:
The spherical microlenses on the front surface act as optical redirectors that take incident light and reflected light and redirect them back toward the viewer's direction. This curved optical structure improves the viewing experience by ensuring more light returns to the viewer while reducing the portion of light lost to other directions.
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 solution significantly increases the perceived brightness of the display by effectively doubling the luminance to exitance ratio, allowing for a brighter and more efficient reflective display experience.
Implementation Method 1
a front sheet having a plurality of partially embedded high refractive index transparent convex protrusions... light being substantially reflected back to the viewer in a semi-retro-reflective manner
Implementation Method 2
light extractor elements to redirect light in a perpendicular direction
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
The disclosure generally relates to a front-lit display having transparent and selectively emissive light directionality. The disclosed semi-retro-reflective, semi-specular and specular displays include directional front light systems that reflect light in a manner to preserve the non-Lambertian characteristic of the light output. This leads to brighter displays with a higher degree of luminance as compared to conventional microencapsulated electrophoretic displays with substantially Lambertian reflectance where much of the light is not reflected back towards the viewer.