Backlight Unit Symmetric Brightness via Segmented Diffraction
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Solution Overview
Problem
Existing liquid crystal display devices with backlight units suffer from asymmetric brightness values when viewed from different angles, leading to uneven image brightness regardless of the viewing direction.
Innovation Solution
A backlight unit configuration featuring a light guide plate, first and second light sources, and corresponding diffraction elements with periodic structures of 440 to 520 nm, including a cholesteric liquid crystal layer, to symmetrically distribute light emission and adjust brightness independently, ensuring consistent brightness across polar angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single diffraction element is used in the backlight unit, then the device complexity is reduced, but the brightness values become asymmetric when viewed from different angles
Solution Approach 1:
The single diffraction element is segmented into two separate diffraction elements with different periodic structures. The first diffraction element has a periodic structure with period P1, and the second diffraction element has a periodic structure with period P2. This segmentation allows each element to diffract light at different angles, achieving symmetric brightness distribution when viewed from opposite directions while maintaining relatively simple device structure
Solution Approach 2:
Two diffraction elements with asymmetric periodic structures (different periods P1 and P2) are used to compensate for the inherent asymmetry in light diffusion. By carefully designing the different periodic structures, the system achieves symmetric brightness values when viewed from opposite angles, effectively resolving the brightness asymmetry problem
2Object-affected harmful factors
If the viewing angle is narrowed to prevent peeping, then security is improved, but visibility from oblique directions deteriorates
Solution Approach 1:
The backlight unit dynamically adjusts the viewing angle characteristics by switching between two diffraction elements with different periodic structures. When security is prioritized, the system can emphasize narrower viewing angles; when oblique visibility is needed, it can switch to configurations that provide wider viewing angles, thus adaptively balancing security and usability
Solution Approach 2:
The system changes the optical parameters by selecting different diffraction elements with different periodic structures (P1 and P2). This allows the viewing angle characteristics to be adjusted according to different usage scenarios, enabling the display to provide both peeping prevention and good oblique visibility as needed
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 enables symmetric brightness values on both sides of the polar angle, providing an image with uniform brightness regardless of the viewing direction, thereby enhancing the usability of liquid crystal display devices.
Implementation Method 1
diffraction elements with periodic structures of 440 to 520 nm, including a cholesteric liquid crystal layer
Implementation Method 2
including a cholesteric liquid crystal layer
Implementation Method 3
a reflective hologram layer that is provided on an upper surface or a lower surface of the light guide plate
Implementation Method 4
a reflector that is disposed below the light guide plate
Data Source
AI summary
Provided are a backlight unit and a liquid crystal display device including the backlight unit, the backlight unit being capable of switching between viewing angles in the liquid crystal display device and having a configuration in which the brightness values of emitted light on the “+” side and the “−” side at a polar angle with respect to the normal line are symmetric to each other. The backlight unit includes: a light guide plate; a first light source that guides light into the light guide plate from a long side or a short side of the light guide plate; a second light source that guides light into the light guide plate from a side of the light guide plate different from that of the first light source; a first diffraction element that is provided on one main surface of the light guide plate and diffracts only light emitted from one of the first light source or the second light source; a second diffraction element that is provided on another main surface of the light guide plate and diffracts only light emitted from another one of the first light source or the second light source; and a reflection plate that is provided on a surface of the light guide plate opposite to a light emission surface.