Uneven Optical Sheet for Thin Direct-Backlight Luminance Uniformity
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Solution Overview
Problem
Existing technologies fail to sufficiently address non-uniformity of luminance between light sources and areas between light sources on the light emitting surface of direct backlights in liquid crystal displays, particularly in small to medium size displays, which are already reduced in thickness and cannot accommodate further thickness increases for High Dynamic Range (HDR) support.
Innovation Solution
An optical sheet with uneven surfaces is designed such that 30% or more of its minute regions have inclination angles of 30° or more, achieved by approximating these surfaces to flat surfaces and shifting them along an imaginary plane, promoting multiple reflections to enhance luminance uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a large quantity of diffusing agent is provided to the diffusion sheet to improve light diffusibility, then the luminance uniformity is improved, but the non-uniformity of luminance between light sources and areas between light sources cannot be sufficiently addressed
Solution Approach 1:
The patent applies local quality by creating specific uneven regions with predetermined projection areas on the optical sheet surface. These localized uneven portions with controlled inclination angles (30° or more) are strategically positioned to address luminance non-uniformity in specific areas between light sources, rather than uniformly treating the entire surface. This localized approach allows precise control over light reflection characteristics in critical regions.
Solution Approach 2:
The patent changes the surface geometry parameters by controlling the inclination angles of uneven portions to be 30° or more. This parameter change transforms the light reflection characteristics from diffuse scattering to more directional reflection, effectively addressing luminance non-uniformity. The specific inclination angle parameter is crucial for achieving the desired light redistribution effect.
2Illumination intensity
If the distance from light source to diffusion member is increased to erase light source image, then the luminance uniformity is improved, but the thickness of the display increases which is unacceptable for small to medium size displays
Solution Approach 1:
The patent applies preliminary anti-action by pre-forming specific uneven portions on the optical sheet surface before light incidence. These predetermined uneven regions with controlled inclination angles are designed in advance to counteract the luminance non-uniformity that would otherwise occur at short distances. The pre-configured surface geometry proactively compensates for the potential harmful effect of close light source positioning.
Solution Approach 2:
The patent utilizes surface curvature by creating uneven portions with specific inclination angles on the optical sheet. These curved or angled surface features modify the light path through reflection and refraction, enabling effective light diffusion and uniformity improvement without requiring increased distance from the light source. The surface curvature acts as an optical element to control light distribution.
3Illumination intensity
If techniques such as arranging lenses with recesses or positioning LED light sources in specific patterns are used, then the luminance uniformity is partially improved, but the non-uniformity between light sources and areas between light sources still cannot be sufficiently suppressed at reduced thickness
Solution Approach 1:
The patent applies local quality by creating specific uneven regions with predetermined projection areas on the optical sheet surface. These localized uneven portions with controlled inclination angles (30° or more) are strategically positioned to address luminance non-uniformity in specific areas between light sources, rather than uniformly treating the entire surface. This localized approach allows precise control over light reflection characteristics in critical regions.
Solution Approach 2:
The patent employs a composite approach by combining the optical sheet with specific surface unevenness features alongside the diffusion sheet containing diffusing agents. This composite structure integrates multiple light control mechanisms (reflection from uneven portions and diffusion from the diffusion sheet) to achieve superior luminance uniformity that neither component could achieve alone, particularly in suppressing non-uniformity between light sources and areas.
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 reduces non-uniformity of luminance between light sources and areas between sources, even at reduced distances, thereby improving luminance uniformity and supporting HDR in thinner liquid crystal displays.
Implementation Method 1
promoting multiple reflections to enhance luminance uniformity
Data Source
Figure 1
Figure 2~3
Figure 4A~4B
AI summary
An optical sheet 43 has at least one surface with unevenness. A total area of some of minute regions, which have surfaces inclined at inclination angles of 30° or more from an imaginary plane that is a flat surface appearing after imaginarily removing the unevenness, accounts for 30% or more of a total area of all the minute regions, for which the inclination angles are obtained by approximating the surfaces of the minute regions with the unevenness to flat surfaces, while two-dimensionally shifting the minute region with a predetermined projection area with respect to the imaginary plane at equal intervals along the imaginary plane to obtain the minute regions at respective points on the imaginary plane.