Edge-Lit Backlight Color Uniformity via Segmented Light Sources
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Solution Overview
Problem
Lighting devices with edge light type backlight units exhibit color unevenness, with the edge regions being tinted more towards the primary light color due to fewer retroreflections, resulting in a bluish tint compared to the center region.
Innovation Solution
Incorporating inner and outer light sources with wavelength converting members, such as phosphors, to emit complementary color light rays, ensuring that the light exiting from the lighting device is less tinted towards the primary light color at the edge portions than at the center, by using quantum dot phosphors like green and red phosphors to convert blue light into yellow, green, and red light respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single light source line with LEDs is used to illuminate the light guide plate, then the structure is simple and compact, but color unevenness occurs where edge regions are tinted blue compared to the center region
Solution Approach 1:
The light source line is segmented into multiple independent light sources: inner light sources positioned at the center and outer light sources positioned at the edges. This segmentation allows different regions to emit different spectral compositions, with outer light sources providing complementary wavelengths to compensate for the blue tint in edge regions, thereby achieving color uniformity across the display surface.
Solution Approach 2:
Different regions of the light source line are assigned different optical characteristics. Outer light sources are configured to emit light with complementary color properties (yellow-green range) compared to the blue-rich light from inner sources. This local differentiation in spectral quality compensates for the wavelength conversion deficiency at light guide plate edges, achieving uniform color output across the entire surface.
2Loss of energy
If quantum dot phosphors are used in the wavelength converting member, then wavelength conversion efficiency is improved, but the edge regions still exhibit blue tint due to insufficient retroreflections
Solution Approach 1:
The lighting system is divided into multiple light source groups (inner and outer light sources) that can be independently controlled. This segmentation enables the outer light sources to specifically address the color deficiency at light guide plate edges by emitting complementary wavelengths, compensating for the insufficient retroreflections in those regions while maintaining high overall conversion efficiency.
Solution Approach 2:
The spectral parameters of light sources are changed across different positions. Outer light sources emit light with peak wavelengths in the yellow-green range (complementary to blue), while inner light sources emit blue-rich light. This spatial variation in spectral parameters compensates for the position-dependent retroreflection effects, achieving uniform color output despite varying conversion efficiencies across the light guide plate.
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 reduces color unevenness by ensuring that the light exiting from the edge portions of the lighting device is less tinted blue, matching the center's color uniformity, thereby improving the display's color consistency.
Implementation Method 1
The phosphor sheet contains quantum dot phosphors. In such a lighting device, some of primary light rays emitted by LEDs (e.g., blue light rays) which reach the phosphor sheet excite the quantum dot phosphors in the phosphor sheet and the rest of the light rays pass through the phosphor sheet. When the quantum dot phosphors are excited by the primary light rays, the quantum dot phosphors emit secondary light rays with wavelengths different from those of the primary light rays (e.g., green light rays and red light rays).
Implementation Method 2
A liquid crystal display device includes a liquid crystal panel and a lighting unit (a backlight unit) configured to supply light to the liquid crystal panel. As an example of such a backlight unit, an edge light type backlight unit (or a side light type backlight unit) has been known. In such a backlight unit, light emitting diodes (LEDs) are disposed along an end surface of a light guide plate.
Data Source
AI summary
A lighting device includes a light source line, a light guide plate, and a wavelength converting member. The light source line includes an inner light source and outer light sources. The inner light source is disposed in the middle and configured to emit primary light rays in a predefined wavelength range. The outer light sources are disposed outer than the inner light source and configured to emit primary light rays and complementary color light rays. The light guide plate includes a light entering surface and a light exiting surface. The wavelength converting member contains first phosphors configured to emit secondary light rays in a wavelength range different from the wavelength range when excited by the primary light rays. The wavelength converting member is disposed to cover the light exiting surface and configured to pass some of the primary light rays and to release planar light.