Prism Sheet Light Diffusion for Vehicle LCD Contrast
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Solution Overview
Problem
Liquid crystal display devices with backlights and prism sheets experience a decrease in both front and oblique contrast ratios due to side lobes caused by the prism sheets, leading to light leakage in black display states, especially when viewed from oblique angles, which is problematic for vehicle-mounted displays.
Innovation Solution
A liquid crystal display device configuration that includes a first polarizer, a liquid crystal panel, a second polarizer, a biaxial retarder with its slow axis parallel to the second polarizer, and a prism sheet with prisms arranged in multiple columns, where the prism sheet has a light diffusion property curve with no side lobes or side lobes having a ratio of local maximum to local minimum luminance of 1.35 or less, and optionally a diffuser sheet with a haze of 12% to 85% to reduce light leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a prism sheet is added to the backlight to focus light to the front, then the front contrast ratio is improved, but side lobes are generated that cause light leakage in oblique directions and decrease the oblique contrast ratio
Solution Approach 1:
A polarizer louver is introduced as an intermediary element between the prism sheet and the liquid crystal panel. This polarizer louver selectively blocks the side lobe light components that cause oblique light leakage while allowing the main light components to pass through, thereby resolving the contradiction between improving front contrast ratio and preventing oblique light leakage
Solution Approach 2:
The invention changes the optical parameters of the system by introducing a polarizer louver with specific polarization characteristics. By controlling the polarization state of light and using the polarizer louver to block specific polarization components, the system achieves reduced oblique light leakage while maintaining front contrast ratio
2Object-affected harmful factors
If a polarizer louver is applied to reduce light leakage in oblique direction, then the oblique contrast ratio is improved, but the front contrast ratio decreases
Solution Approach 1:
The invention optimizes the parameters of the polarizer louver, including its polarization angle, thickness, and material properties, to achieve a balance where oblique light leakage is reduced without significantly compromising front contrast ratio. By carefully controlling these parameters, both front and oblique contrast ratios can be maintained at acceptable levels
3Illumination intensity
If the prism sheet focuses large-polar-angle light to the front, then front visibility is improved, but the light is emitted at larger polar angles as side lobe light causing oblique viewing degradation
Solution Approach 1:
The polarizer louver acts as a mediator that selectively filters side lobe light components while allowing main light components to pass. By positioning the polarizer louver between the prism sheet and the liquid crystal panel, it intercepts the side lobe light before it enters the liquid crystal panel, preventing oblique viewing degradation while preserving front luminance
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 effectively reduces or prevents the decrease in both front and oblique contrast ratios, enhancing display visibility and compliance with OEM standards by minimizing light leakage in black states and maintaining high contrast ratios.
Implementation Method 1
a prism sheet disposed closer to the viewing surface side than the light source is with an aim of focusing light from the light source to the front
Implementation Method 2
applying voltage to a liquid crystal layer containing a liquid crystal composition sealed between a pair of substrates to change the alignment state of liquid crystal molecules
Implementation Method 3
a first polarizer having a first transmission axis; a liquid crystal panel; a second polarizer having a second transmission axis; a biaxial retarder having a slow axis parallel to the second transmission axis; a third polarizer having a third transmission axis parallel to the second transmission axis
Data Source
AI summary
Provided is a liquid crystal display device sequentially including: a first polarizer; a liquid crystal panel; a second polarizer; a biaxial retarder; a third polarizer; and a backlight including a light source and a prism sheet disposed closer to the viewing surface side than the light source is. The prism sheet includes prisms arranged in multiple columns on a surface close to the viewing surface side. The liquid crystal display has a light diffusion property curve having no side lobe or having a side lobe satisfying a ratio of a local maximum luminance to a local minimum luminance of 1.35 or less, the light diffusion property curve being obtained by plotting a luminance in a white display state in a direction perpendicular to ridge lines of the prisms against a polar angle.