Privacy Display with Switchable Liquid Crystal Retarder
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Solution Overview
Problem
Existing privacy displays face challenges in controlling illumination to maintain visual security while ensuring high image contrast for on-axis viewers and reducing visibility for off-axis snoopers, especially under varying ambient light conditions, due to high losses in head-on illumination and potential Moiré artefacts from micro-louvre optical films.
Innovation Solution
A display apparatus with a selectively operable luminance-privacy and contrast-privacy optical arrangement, controlled by an ambient light sensor, which adjusts the luminance and contrast of the image to maintain visual security by using a switchable liquid crystal retarder and passive compensation retarders between polarisers, and a directional waveguide to direct light effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If micro-louvre optical films are used to provide privacy function, then off-axis visibility is reduced, but head-on illumination losses increase and Moiré artefacts occur
Solution Approach 1:
The patent employs switchable optical arrangements including liquid crystal layers and electrochromic layers that can dynamically change their optical properties based on applied voltage. This allows the display to switch between transparent and opaque states, or adjust privacy levels dynamically, resolving the contradiction by enabling selective control of light transmission rather than fixed micro-louvre structures that cause permanent illumination losses
Solution Approach 2:
The patent changes the optical parameters of the display by using liquid crystal layers with different refractive indices and electrochromic layers with variable absorption coefficients. By adjusting these parameters through voltage control, the system can achieve both high head-on illumination efficiency and effective off-axis privacy protection without the fixed geometric constraints of micro-louvres
2Object-affected harmful factors
If micro-louvre optical films are used to provide privacy function, then off-axis visibility is reduced, but Moiré artefacts are caused due to beating with pixels
Solution Approach 1:
The patent replaces the mechanical micro-louvre structure with electro-optical materials (liquid crystal and electrochromic layers) that control light through electrical fields rather than physical geometric structures. This substitution eliminates the periodic micro-structure that causes Moiré interference with display pixels while maintaining the privacy function through controlled light absorption and refraction
3Object-affected harmful factors
If contrast-privacy arrangement is operated in low ambient light, then visual security is improved, but image contrast for on-axis viewer is reduced
Solution Approach 1:
The patent uses an ambient light sensor to dynamically control the operation of the contrast-privacy arrangement. In low ambient light conditions, the system automatically disables or reduces the operation of contrast-reducing optical elements, while in high ambient light conditions, the system activates these elements to enhance visual security. This dynamic adaptation resolves the contradiction by matching privacy enhancement to actual environmental conditions
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 ensures high contrast for on-axis viewers in high ambient illuminance environments while maintaining desirable visual security for off-axis snoopers, minimizing contrast reduction to enhance image visibility for head-on users as ambient light levels change.
Implementation Method 1
a layer of liquid crystal material and electrodes arranged to apply a voltage for switching the layer of liquid crystal material
Implementation Method 2
The first and second optical arrangements may each comprise a liquid crystal layer
Implementation Method 3
Display backlights in general employ waveguides and edge emitting sources
Implementation Method 4
The display device having a selectively operable luminance-privacy optical arrangement arranged on operation to reduce the luminance of the image to an off-axis viewer
Data Source
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AI summary
A privacy display comprises a luminance-privacy arrangement and a contrast-privacy arrangement. In a privacy mode of operation, ambient light levels are detected and a visual security level is calculated. At and above a visual security level threshold the luminance-privacy arrangement is operable and below the threshold both the luminance-privacy and contrast-privacy arrangements are operable. Image quality for on-axis users is optimised and high levels of visual security are achieved for off-axis snoopers over a wide range of display illuminance conditions.