Planar Waveguide Display for Ambient Light Discrimination
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Solution Overview
Problem
Existing projection screens are not effective in high ambient light environments, such as those with direct sunlight, as they either suffer from image saturation or reduced brightness, and previous attempts to mitigate this have compromised the ability to produce high brightness images.
Innovation Solution
A display system utilizing a planar waveguide with collocated optic fibers that discriminates between incident light angles, guiding light within the acceptance range while reflecting ambient light outside this range, thereby preventing image saturation and maintaining high brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the projection screen material is darkened to reduce reflected light, then ambient light saturation is reduced, but the capability to produce high brightness images is lowered
Solution Approach 1:
The projection screen is designed with spatially varying optical properties: it has high reflectivity for light incident from the projector (within the acceptance cone) and low reflectivity for ambient light (outside the acceptance cone). This local differentiation of optical characteristics allows the screen to selectively enhance desired light while rejecting unwanted ambient light, resolving the contradiction between brightness and saturation resistance
Solution Approach 2:
The screen material's reflectivity parameter is made angle-dependent through the use of microstructured surfaces or specific material properties. The reflectivity varies based on the incidence angle of light, being high for angles within the acceptance cone (projector light) and low for angles outside it (ambient light). This parameter change enables the screen to maintain high brightness for projected images while resisting saturation from ambient light
2Illumination intensity
If the projection screen is designed for diffuse reflection to maximize apparent brightness, then image brightness is improved, but black levels become brighter and saturation occurs in high ambient light
Solution Approach 1:
Instead of uniform diffuse reflection, the screen employs localized directional reflection characteristics. The microstructured surface creates regions that preferentially reflect light from specific directions (projector) while absorbing or transmitting light from other directions (ambient sources). This local quality differentiation maintains apparent brightness for projected images while preventing saturation from ambient light
Solution Approach 2:
The screen's reflection pattern is made asymmetric with respect to light source direction. It exhibits strong reflection symmetry for light incident from the projector's direction but asymmetric suppression for ambient light coming from various other angles. This asymmetry in optical response allows the screen to enhance projected image brightness while selectively rejecting ambient light that would cause saturation
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 system effectively discriminates against ambient light, ensuring clear image projection in high ambient light conditions without compromising image brightness or contrast, making it suitable for day and night digital signage applications.
Implementation Method 1
the planar waveguide is adapted to guide incident light within the incidence angle acceptance range
Implementation Method 2
the incident ambient light reflects off the front surface of the projection screen, therefore preventing the ambient light (sunlight) from saturating the projection surface material
Data Source
AI summary
A display system for ambient light discrimination comprising: a planar waveguide comprising a plurality of collocated optic fibers wherein, the planar waveguide is adapted to guide incident light within the incidence angle acceptance range and wherein the planar waveguide is adapted to guide light along a bias trajectory, wherein, in use, the display system is adapted for discriminating against incident light outside an incidence angle acceptance range.