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 light uniformly.
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 light diffusion sheet is divided into multiple functional regions: a light incident surface with first凹凸 structures for initial light diffusion, a light emission surface with second凹凸 structures for enhanced diffusion, and an intermediate layer with third凹凸 structures. This segmentation allows each surface to contribute to light diffusion at different stages, achieving sufficient uniformity even when the overall sheet thickness is reduced.
Solution Approach 2:
The invention transitions from single-surface diffusion to multi-surface diffusion by adding凹凸 structures on both the light incident surface and light emission surface, as well as intermediate structures. This dimensional expansion from one-sided to multi-sided light interaction enables effective light diffusion in a thinner profile.
2Length of stationary object
If the thickness of the light diffusion sheet is reduced, then the overall device thickness is reduced, but the light diffusion effectiveness decreases
Solution Approach 1:
Different surfaces of the light diffusion sheet are given different local qualities: the light incident surface has first凹凸 structures optimized for receiving and initial diffusing light, the intermediate layer has third凹凸 structures for further diffusion, and the light emission surface has second凹凸 structures for final diffusion. This localized optimization of diffusion characteristics at different depths compensates for the reduced overall thickness.
Solution Approach 2:
The first凹凸 structures on the light incident surface perform preliminary light diffusion before light enters the intermediate layer and reaches the emission surface. This preliminary action ensures that light is already partially diffused before traversing the thinner sheet, maintaining diffusion effectiveness despite reduced thickness.
3Length of moving object
If light sources are disposed immediately under the display screen, then the distance to the light diffusion sheet is reduced enabling thickness reduction, but in-plane luminance uniformity deteriorates
Solution Approach 1:
The light diffusion path is segmented into multiple stages with凹凸 structures distributed across the light incident surface, intermediate layer, and light emission surface. This segmentation allows light to be progressively diffused over a longer effective path length, compensating for the reduced physical distance between light sources and the diffusion sheet.
Solution Approach 2:
The multiple surfaces with凹凸 structures create dynamic light diffusion pathways, where light undergoes multiple refraction and reflection events as it passes through different layers. This dynamic multi-stage diffusion process enhances uniformity even when the overall distance from light sources is reduced.
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 improved 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
Figure 1~2
Figure 3~4
Figure 5
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.