Prismatic Film Light Guide for Uniform LCD Illumination
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Solution Overview
Problem
Conventional LCD backlights, especially those using LEDs, are costly and bulky due to the need for multiple LEDs or gaps to distribute light uniformly, and often require expensive high-index plastics and large molds for wedge-shaped light guides, while prismatic films are inefficient for uniform illumination across large screens.
Innovation Solution
A light guide system utilizing a pair of prismatic films with a low-index layer and a cover layer, where the prismatic films are coated with a low-index material and a high-index material, and optionally curved to ensure uniform illumination, allowing rays to undergo the same number of reflections regardless of injection angle, combined with folding prisms made of inexpensive low-index plastic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If many light-emitting diodes are used to fill the area of a panel, then uniform illumination is achieved, but device complexity and cost increase
Solution Approach 1:
The light guide is divided into two functional sections: a constant thickness section for initial light distribution and a wedge section for further spreading. This segmentation allows a single LED to illuminate the entire panel area uniformly without requiring multiple LEDs.
Solution Approach 2:
The invention transitions from a two-dimensional array of LEDs to a three-dimensional light guide structure with varying thickness. By utilizing the thickness dimension and creating a wedge shape, the system achieves area coverage that would otherwise require multiple light sources.
2Device complexity
If a wedge-shaped light guide is used to spread illumination, then fewer light sources are needed, but bands appear in the illumination pattern
Solution Approach 1:
The light guide is segmented into a constant thickness section and a wedge section. The constant thickness section ensures all rays undergo the same number of reflections, preventing band formation, while the wedge section spreads the illumination across the panel area.
Solution Approach 2:
One side of the wedge is curved according to a specific profile rather than being straight. This curvature compensates for the varying path lengths of rays at different angles, ensuring uniform illumination and eliminating bands in the illumination pattern.
3Volume of moving object
If high-index folding prisms are used to prevent protrusion, then compact design is achieved, but manufacturing cost increases
Solution Approach 1:
The invention replaces expensive high-index plastic folding prisms with a thin layer of low-index material (such as air or a thin polymer layer) between the prismatic films. This achieves the same optical function at a fraction of the material cost.
Solution Approach 2:
The invention changes the refractive index parameter from high-index material to low-index material (such as air with n≈1.0) in the folding section. This parameter change allows the use of inexpensive materials while maintaining the compact folded design.
4Area of stationary object
If wedge panels large enough to illuminate a big LCD are manufactured, then coverage area is achieved, but manufacturing time and material volume increase
Solution Approach 1:
The light guide is segmented into a thin constant thickness section and a wedge section. The thin constant thickness section can be manufactured quickly with minimal cooling time, while the wedge section provides the necessary area coverage.
Solution Approach 2:
The invention uses a thin constant thickness section (on the order of micrometers) that can be manufactured rapidly using thin-film techniques. This thin film approach dramatically reduces manufacturing time and material volume compared to solid wedge panels.
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 solution provides a lightweight, inexpensive, and efficient backlight that distributes light uniformly across an LCD, reducing material usage and manufacturing costs while maintaining uniform illumination, even with a single LED source.
Implementation Method 1
They are almost perfect reflectors for light incident in a plane perpendicular to the film and containing the axis of a prism
Implementation Method 2
Light can be guided between two spaced sheets of prismatic film with parallel axes provided that the component of wave vector perpendicular to the prism axes is not large
Data Source
Figure 1~2
Figure 3~5
Figure 6
AI summary
A selectively light-reflecting sheet (30) includes a prismatic film (1) with parallel prisms (10) on its face, a low- index film (3) on the prisms and a layer (5) on the low-index film, this layer having a substantially flat surface. This results in a low effective index, which means that light incident at steeper angles on the prismatic film (1) will pass through it. This "leaky" effect can be used in conjunction with a reflector sheet (20) in a tapered-waveguide arrangement to construct a lightweight backlight.