Optical Sheet Ultrafine Grooves Backlight Hot Spot Control
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Solution Overview
Problem
Liquid crystal display devices with edge-lit backlight units using LEDs suffer from hot spots due to the diffusion of highly directive light rays, leading to uneven luminance, which worsens with thinner units, higher luminance LEDs, fewer LEDs, and larger screens.
Innovation Solution
An optical sheet with ultrafine grooves oriented in specific directions on at least one resin layer is used to inhibit hot spots by diffusing light rays, with an average groove density of 10 to 10,000/mm and an arithmetic average roughness of 0.01 to 5 μm, potentially forming a diffraction grating to manage light distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional light diffusion sheets are used to diffuse light from LEDs, then light diffusion is achieved, but hot spots are created causing non-uniform luminance
Solution Approach 1:
The optical sheet is divided into multiple resin layers with different structures. The first resin layer contains ultrafine grooves for primary light diffusion, while the second resin layer has a different refractive index for secondary diffusion. This segmentation allows progressive control of light distribution to eliminate hot spots while maintaining luminance uniformity.
Solution Approach 2:
The ultrafine grooves are formed only in specific regions where hot spots occur, rather than uniformly across the entire optical sheet. This localized treatment targets the problematic areas while preserving light transmission in other regions, achieving hot spot inhibition without compromising overall luminance uniformity.
2Ease of manufacture
If the number of LEDs is reduced to lower cost, then manufacturing cost decreases, but hot spots become more conspicuous
Solution Approach 1:
The invention changes the optical parameters of the light diffusion sheet by introducing ultrafine grooves with specific dimensions (width of 1-10 μm, depth of 1-10 μm) and controlling the groove density (10-1000 grooves per 10 mm). These parameter changes enhance the light diffusion capability, allowing fewer LEDs to be used while maintaining luminance uniformity and preventing hot spots.
3Illumination intensity
If high-luminance LEDs are used to increase brightness, then illumination intensity increases, but hot spots are created
Solution Approach 1:
The ultrafine grooves act as an intermediary structure between the high-luminance LEDs and the display panel. These grooves diffuse the concentrated light from the LEDs before it reaches the display, converting the highly directional light into more uniform illumination and preventing hot spots while maintaining high brightness.
4Length of moving object
If the thickness of the backlight unit is reduced to make the display thinner, then device thinness is improved, but hot spots become more conspicuous
Solution Approach 1:
Instead of increasing the thickness of the optical sheet to diffuse light, the invention uses ultrafine grooves with vertical depth components. The grooves extend into the thickness direction of the optical sheet, creating three-dimensional light diffusion paths that effectively scatter light without significantly increasing the overall backlight unit thickness.
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 optical sheet effectively prevents the creation of hot spots by diffusing light uniformly across the display, improving luminance uniformity and reducing iridescent unevenness, even with highly directive LEDs.
Implementation Method 1
the rays of light passing through regions defined by the ultrafine grooves are transmitted in the width direction of the ultrafine grooves
Implementation Method 2
potentially forming a diffraction grating to manage light distribution
Implementation Method 3
an optical sheet with ultrafine grooves oriented in specific directions on at least one resin layer is used to inhibit hot spots by diffusing light rays
Data Source
AI summary
An optical sheet for a backlight unit for guiding toward a front face side rays of light emitted by an LED light source. The optical sheet includes one or more resin layers. Ultrafine grooves oriented in specific directions are provided on a front face side or a back face side of at least one resin layer of the one or more resin layers. An average number of the ultrafine grooves per unit length in a direction perpendicular to an average orientation of the ultrafine grooves is preferably no less than 10/mm and no greater than 10,000/mm. A face of the at least one resin layer provided with the ultrafine grooves preferably has an arithmetic average roughness (Ra) in a direction perpendicular to an orientation of the ultrafine grooves being no less than 0.01 μm and no greater than 5 μm. Ultrafine grooves preferably constitute a diffraction grating.