Light Diffusion Sheet Recess Geometry for Thin Backlight Uniformity
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Solution Overview
Problem
In direct-lit backlights, reducing the distance between light sources and the light diffusion sheet or the thickness of the sheet leads to difficulty in sufficiently diffusing light, resulting in degradation of in-plane luminance uniformity.
Innovation Solution
A light diffusion sheet with a flat light incident surface and internal haze of 1.5% or less, featuring recesses on the emission surface in the form of inverted polygonal pyramids, enhances uniformity by diffusing straight-traveled light without internal diffusion, canceling light source images, and allowing for thinner designs with fewer sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the distance from light sources to the light diffusion sheet or the thickness of the sheet is reduced, then the thickness of the display is reduced, but the light diffusion capability is insufficient leading to degradation of in-plane luminance uniformity
Solution Approach 1:
The light diffusion sheet is divided into two distinct surfaces: a light incident surface with a flat shape and a light emission surface with an uneven shape comprising a plurality of recesses. This segmentation allows each surface to perform its specific function optimally - the flat incident surface ensures uniform light entry while the uneven emission surface provides effective light diffusion, resolving the contradiction between thinness and diffusion capability
Solution Approach 2:
Different surfaces of the light diffusion sheet are given different local qualities - the light incident surface has a flat shape with specific roughness characteristics while the light emission surface has an uneven shape with recesses. This local differentiation enables the thin sheet to maintain both structural integrity and effective light diffusion functionality
2Manufacturing precision
If a light diffusion sheet with embossed light incident surface and inverted pyramidal recesses is used, then light diffusion is enhanced, but internal haze increases reducing light transmission efficiency
Solution Approach 1:
The invention extracts the light diffusion function from the light incident surface and relocates it to the light emission surface. By making the incident surface flat and removing diffusion elements from it, light transmission efficiency is improved while the emission surface's recesses provide the necessary diffusion capability
Solution Approach 2:
Instead of placing diffusion structures on the light incident surface as in conventional designs, the invention inverts this approach by placing the diffusion structures (recesses) on the light emission surface. This inversion allows light to pass through the sheet efficiently while achieving diffusion at the exit surface
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 achieves enhanced in-plane luminance uniformity, enabling further reduction of thickness and number of light sources in liquid crystal displays.
Implementation Method 1
A light diffusion sheet diffuses light incident from a light incident surface by utilizing diffusion caused by an uneven shape on a light emission surface
Data Source
AI summary
A light diffusion sheet 43 includes: a first surface 21a as a light emission surface; and a second surface 21b as a light incident surface. The first surface 21a includes a plurality of recesses 22 each having an approximately inverted polygonal pyramid shape. The second surface 21b has an arithmetic mean roughness of 3.0 μm or less. The light diffusion sheet 43 has an internal haze of 1.5% or less.