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, thereby canceling light source images and improving luminance uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the distance from light sources to the light diffusion sheet and/or the thickness of the light diffusion 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 patent changes the geometric parameters of the recesses (depth, width, shape) and the surface roughness parameter of the light incident surface to optimize light diffusion. By controlling the arithmetic mean roughness to be 3.0 μm or less and designing specific recess dimensions, the sheet achieves effective light diffusion even at reduced thickness, resolving the contradiction between thinness and luminance uniformity.
Solution Approach 2:
The patent employs curved surfaces in the form of inverted pyramidal recesses with specific curvature characteristics. These curved geometric features on the light emission surface effectively scatter and diffuse light, enabling sufficient diffusion capability in a thinner sheet structure, thus resolving the contradiction between reduced thickness and maintained luminance uniformity.
2Illumination intensity
If a light diffusion sheet with internal haze is used to diffuse light, then light diffusion is enhanced, but the straight-traveled high-luminance light is lost and in-plane luminance uniformity degrades
Solution Approach 1:
The patent segments the light diffusion function into two distinct surfaces: a flat light incident surface that preserves straight-traveled light, and a structured light emission surface with inverted pyramidal recesses that provides controlled diffusion. This segmentation allows the sheet to maintain both high luminance from direct light and uniformity from structured diffusion, resolving the contradiction between diffusion capability and luminance uniformity.
Solution Approach 2:
The patent applies different surface qualities at different locations: the light incident surface maintains a flat, smooth quality (arithmetic mean roughness 3.0 μm or less) to preserve direct light transmission, while the light emission surface features inverted pyramidal recesses for localized diffusion. This local differentiation resolves the contradiction by ensuring straight-traveled light is maintained where needed while providing diffusion where required.
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, allowing for further reduction in thickness and number of light sources, while maintaining high luminance.
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
Implementation Method 2
light incident from the second surface reaches the first surface as an uneven surface substantially without being diffused in the sheet
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.