Light Guide Plate Prism Angles for Uniform Backlight
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Solution Overview
Problem
Edge-light-type backlight units for compact liquid-crystal display devices suffer from dark areas near LEDs due to light directivity and reduced effectiveness of reflecting prisms at larger radiation angles, leading to uneven backlight luminance.
Innovation Solution
A light guide plate with reflecting prisms having first and second slant surfaces, where the inclination angles of the second slant surfaces near the incident surface are increased and those further away are decreased, allowing a larger portion of reflected light to be emitted from the area near the incident surface, and a reflective film on the second side surface enhances light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If reflecting prisms with uniform slant surfaces are used in the light guide plate, then light is reflected effectively at small radiation angles, but dark areas appear near the incident surface where light directivity causes reduced emission
Solution Approach 1:
The patent applies local quality by making the slant surfaces of reflecting prisms non-uniform: prisms near the incident surface have larger slant angles while those farther away have smaller slant angles. This spatial variation in prism geometry compensates for the directivity effect of LEDs, ensuring uniform light emission across the entire light guide plate surface and eliminating dark areas near the incident surface.
2Length of moving object
If the light guide plate thickness is reduced to make compact display devices, then the overall size is decreased, but light propagation and reflection efficiency is compromised
Solution Approach 1:
The patent changes the geometric parameters of the reflecting prisms by introducing non-uniform slant angles that vary with position. This parameter variation optimizes light reflection efficiency throughout the light guide plate, maintaining effective light utilization even when the plate thickness is reduced for compact device design.
3Use of energy by moving object
If LEDs are positioned close to the light guide plate for efficient light coupling, then light entry efficiency is improved, but dark areas appear near the LED positions due to directivity effects
Solution Approach 1:
The patent addresses the directivity problem by implementing local quality variation in the prism slant angles. Prisms located near the incident surface where LED directivity causes dark areas have larger slant angles to redirect more light toward the emission surface, while prisms farther away have smaller angles. This creates uniform illumination across the entire surface while maintaining efficient light coupling from the LEDs.
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
This configuration significantly reduces dark areas and enhances backlight luminance by effectively redirecting and emitting light from the light guide plate's top surface near the incident surface, improving uniformity and overall light usage.
Implementation Method 1
Light emitted from the LEDs 3 enters the light guide plate 2 from the side surface 2a and propagates inside the light guide plate 2 while being repeatedly reflected on a bottom surface 2b and a top surface 2c of the light guide plate 2
Implementation Method 2
the incident angle of light from the LEDs 3 with respect to the top surface 2c serving as a light-emitting surface gradually decreases as the light propagates while being repeatedly reflected on the top surface 2c and the bottom surface 2b. When the incident angle becomes smaller than a predetermined critical angle, the light is emitted from the light-emitting surface to the outside
Data Source
AI summary
A light guide plate includes a top surface serving as a light-emitting surface, a bottom surface serving as a reflecting surface, and a periphery having a first side surface serving as an incident surface and a second side surface opposite the first side surface. The bottom surface is provided with reflecting prisms successively arranged in a direction from the first to second side surface. Each reflecting prism has a first slant surface and a second slant surface succeeding to the first slant surface. The first slant surface extends toward the top surface in a direction from the first side surface toward the second side surface and the second slant surface extends away from the top surface in the same direction. The second slant surface is formed such that a large part of light reflected back from the second side surface toward the first side surface is emitted from an area of the top surface near the first side surface.