Planar Lighting Device With Variable Thickness Light Guide Plate
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Solution Overview
Problem
Current planar lighting devices for large-size liquid crystal televisions face challenges in achieving a thin, high-light-use-efficiency design with minimal luminance unevenness, as existing solutions either compromise on thickness, increase weight, or elevate processing costs due to complex shapes and materials.
Innovation Solution
A planar lighting device featuring a light guide plate with a two-layer structure and micro-lens film, where the light guide plate has scattering particles dispersed at varying concentrations and a micro-lens film with spherical micro-ball lenses to optimize light distribution and reduce return light, achieving a bell-shaped brightness distribution and improved front luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional underneath type backlight unit is used to ensure uniform light distribution, then light amount distribution is uniform, but the thickness becomes about 30 mm which is too large
Solution Approach 1:
The patent changes the thickness parameter of the light guide plate from uniform to variable, creating a wedge shape where thickness decreases from the light source side toward the exit surface. This parameter change allows the light guide plate to achieve uniform light distribution while reducing overall thickness to approximately 5mm, resolving the contradiction between uniform illumination and thin profile.
2Length of moving object
If a light guide plate with complex shape is used to reduce thickness, then thickness is reduced, but processing costs increase due to complex shapes
Solution Approach 1:
The wedge-shaped light guide plate employs a simple linear thickness variation that can be manufactured using conventional molding techniques. This straightforward geometric parameter change avoids complex multi-cavity molds or assembly steps, keeping processing costs low while achieving the desired thin profile.
3Stability of the object's composition
If scattering particles are uniformly dispersed in the light guide plate, then light scattering is consistent, but luminance unevenness and visible bright lines occur
Solution Approach 1:
The patent applies local quality by concentrating scattering particles in specific regions: a first scattering region near the light source with higher particle density to control initial light distribution, and a second scattering region near the exit surface with lower particle density to prevent excessive scattering. This localized differentiation eliminates visible bright lines while maintaining overall luminance uniformity.
4Length of moving object
If the light guide plate thickness is reduced, then thickness is reduced, but light use efficiency decreases
Solution Approach 1:
The wedge-shaped thickness profile optimizes light extraction efficiency by controlling the optical path length. Light enters at the thicker end where it can travel through the high-refractive-index material and exit at the thinner end, maximizing the opportunity for light extraction while minimizing reflections and losses. This parameter optimization maintains high light use efficiency despite the reduced overall 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 solution enables a thin, efficient lighting device with reduced luminance unevenness and increased light use efficiency, enhancing the brightness distribution and preventing visible bright lines, while minimizing material and processing costs.
Implementation Method 1
scattering particles for scattering light which are dispersed in a transparent resin
Implementation Method 2
an optical member unit including a micro-lens film in which a plurality of spherical micro-ball lenses are formed
Data Source
AI summary
There is provided a planar lighting device which can emit light with high light use efficiency and small luminance unevenness. This object is achieved by having a light guide plate including two or more layers overlapping in a direction perpendicular to a light exit surface and having different particle concentrations of the scattering particles, thicknesses of the layers in the direction perpendicular to the light exit surface varying so that a combined particle concentration has, in a direction perpendicular to a light incidence surface, a first local maximum value closer to the light incidence surface and a second local maximum value located farther from the light incidence surface than the first local maximum value and being larger than the first local maximum value; and a micro-lens film having a plurality of spherical micro-ball lenses formed on a film.