Planar Illumination Device with Polygonal Light Guide Plate
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Solution Overview
Problem
Existing backlights for handheld devices using LEDs suffer from irregular color distribution and luminance variations, leading to increased thickness and weight, and reduced luminous efficiency due to the placement and spacing of point light sources.
Innovation Solution
A directly-beneath type planar illumination device with a color-mixing structure using a polygonal light guide plate and strategically placed LED chips emitting primary colors, combined with reflection and diffusion sheets to ensure even color mixing and luminance distribution, while maintaining low power consumption and thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If LED chips are placed close together to mix colors, then color mixing efficiency improves, but temperature increases and luminous efficiency decreases
Solution Approach 1:
The backlight unit is divided into multiple independently controllable LED chip groups (red, green, blue) that can be controlled separately. This allows color mixing to be achieved through spatial arrangement and independent control rather than close physical proximity, reducing heat accumulation while maintaining color mixing efficiency.
Solution Approach 2:
The patent transitions from one-dimensional linear arrangement of LEDs to two-dimensional matrix arrangement on the light guide plate. This dimensional change allows for better heat dissipation distribution and more effective color mixing through optical paths without requiring LEDs to be in close contact.
2Stability of the object's composition
If distance between LED chips and display panel is increased to improve color mixing, then color uniformity improves, but backlight thickness increases
Solution Approach 1:
A light guide plate with specific optical properties is introduced as an intermediary between the LED chips and the display panel. The light guide plate diffuses and redirects light from the LEDs, achieving uniform color distribution across the display surface without requiring increased distance, thus maintaining thin profile.
Solution Approach 2:
The patent changes the optical parameters of the light guide plate (refractive index, thickness, surface structure) to optimize light diffusion and color mixing. By adjusting these parameters, uniform color distribution is achieved while keeping the backlight thickness minimal.
3Stability of the object's composition
If characteristic variations among LEDs are reduced to achieve even color distribution, then color uniformity improves, but manufacturing complexity increases
Solution Approach 1:
Different LED chip groups (red, green, blue) are positioned at specific locations on the light guide plate where their light can be optimally mixed. The patent applies local quality by assigning specific functions to specific positions, allowing tolerance for individual LED variations while achieving overall uniformity through strategic placement.
Solution Approach 2:
The patent adjusts manufacturing parameters such as LED chip placement positions, light guide plate optical properties, and driving current ratios to compensate for LED characteristic variations. This allows production of uniform color output without requiring extremely tight control over individual LED specifications.
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 even color and luminance distribution, reduces device thickness and weight, and maintains high luminous efficiency, enabling a compact, high-brightness, and high-quality liquid crystal display device.
Implementation Method 1
The LEDs are attached on the side surface of a transparent plate (light guide plate) made of acryl plate or the like
Implementation Method 2
While being propagated in the light guide plate, the light emitted from the LED changes its course to the surface of the light guide plate
Implementation Method 3
The backlight using LEDs is characterized by good color reproducibility and generally employs the side edge type using a light guide plate in view of reducing a thickness, weight and power consumption
Data Source
AI summary
A planar illumination device is provided that can achieve even distributions of mixed colors and luminance, downsizing and weight saving without lowering the luminous efficiency of LED chips. In addition, a liquid crystal display device using the planar illumination device as a backlight is provided.A polygonal flat plate-like light guide plate GLB is combined with a plurality of LED chips D1, D2, D3 emitting light with different colors from each other to constitute a color mixing unit DUT. A plurality of the color mixing units are arranged on printed circuit boards RFB having a reflection function to constitute a planar illumination device. The planer illumination device is installed on the back of a liquid crystal display panel, thus constituting a liquid crystal display device.