Light Guide With In-Coupling Gratings for Even LCD Illumination
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Solution Overview
Problem
Existing display panel backlighting systems, such as those used in LCDs, suffer from significant light loss due to reflections and refractions, leading to increased power consumption and component aging, as a substantial portion of the light radiated by LEDs is not effectively utilized for illumination.
Innovation Solution
A light guide with in-coupling and out-coupling structures, including gratings and reflectors, is used to efficiently spread and direct backlight illumination, minimizing losses and enhancing light distribution across the display panel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a relatively thick planar light guide is used with multiple diffusion and prism foils, then even illumination of the LCD is achieved, but significant light loss occurs due to reflections and refractions
Solution Approach 1:
The light guide is divided into multiple functional sections: an input section with in-coupling structures to capture LED light, a middle section with minimal thickness for light propagation, and an output section with out-coupling structures to extract light toward the LCD. This segmentation allows each section to be optimized for its specific function, reducing overall light loss while maintaining even illumination.
Solution Approach 2:
Different regions of the light guide have different optical properties and thicknesses tailored to their specific functions. The input region has higher thickness and in-coupling structures for efficient light capture, the middle region has minimal thickness for low-loss transmission, and the output region has out-coupling structures for controlled light extraction. This local optimization reduces overall light loss while achieving even illumination.
2Illumination intensity
If multiple diffusion and prism foils are stacked, then light diffusion is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
Multiple optical functions (light diffusion, light direction, and light extraction) that were previously achieved through separate stacked foils are merged into an integrated light guide structure with embedded in-coupling and out-coupling structures. This consolidation reduces the number of separate components while maintaining the necessary optical functions, thereby reducing device complexity and manufacturing difficulty.
3Illumination intensity
If a thick light guide plate is used, then light scattering is sufficient, but illumination power loss increases due to multiple reflections and refractions
Solution Approach 1:
The light guide is segmented into functional sections with varying thicknesses. The input section has sufficient thickness for light scattering and coupling, while the middle and output sections have minimal thickness to reduce reflections and refractions. This segmentation maintains necessary light scattering where needed while minimizing power loss in light transport regions.
Solution Approach 2:
The light guide thickness and optical properties are locally optimized: thicker regions with higher scattering capability are placed only where needed for light capture and distribution, while thinner regions with lower loss characteristics are used for light transport. This local quality variation maintains sufficient light scattering while reducing overall illumination power loss.
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 reduces light loss, increasing the effective use of LED illumination, thereby decreasing power consumption and prolonging component lifespan by ensuring more even and efficient backlighting.
Implementation Method 1
The in-coupling grating may be diffractive grating. The diffractive grating may be concentric or radial with the backlight illumination source.
Implementation Method 2
The spreading reflector may comprise reflective material on the output surface.
Implementation Method 3
The in-coupling grating may be configured to form a diverging or negative Fresnel lens configured to laterally spread the received backlight illumination.
Implementation Method 4
The backlight in large screens such as computer monitors and television sets is typically produced by arranging light sources such as light emitting diodes (LEDs) around a relatively thick planar light guide made of clear plastics.
Data Source
AI summary
A rear illuminated light guide for an LCD screen with in-coupling gratings to receive backlight from an input surface and to spread received backlight laterally within the light guide. Out-coupling gratings receive laterally spread backlight and output at least some of the received laterally spread backlight through an output surface that is opposite to the input surface and towards the LCD screen. The input and output gratings have lateral offset.