Planar Illumination Device Yellow Light Absorption
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Solution Overview
Problem
Planar illumination devices using white LEDs experience uneven color due to light rays being tinged with yellow, especially as the configuration becomes thinner, leading to reduced illumination performance and increased visibility of color discrepancies.
Innovation Solution
Incorporating a second coverlay film on the circuit substrate that absorbs light rays inclined with respect to the optical axis, specifically formed into an outline shape aligned with the circuit substrate, to reduce the emission of yellow-tinted light and improve luminance while allowing light rays parallel to the axis to pass through, thereby minimizing uneven color and enabling a thinner design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a white LED is used as a point light source, then the planar illumination device achieves high luminance and energy efficiency, but light rays emitted at angles to the optical axis become tinged with yellow, causing uneven color distribution
Solution Approach 1:
A second coverlay film is introduced as an intermediary element between the LED and the light guide plate. This coverlay film selectively absorbs yellow-tinted light rays that are emitted at angles to the optical axis, while allowing blue light rays (which are less tinged with yellow) to pass through. This mediator resolves the contradiction by filtering out the harmful yellow component without significantly reducing the overall luminance output.
Solution Approach 2:
The second coverlay film is specifically designed with optical properties that target yellow light absorption. By using a material that absorbs yellow wavelengths, the system transforms the spectral composition of the emitted light, reducing the yellow tint in angled rays while preserving the blue component. This color-selective absorption directly addresses the uneven color distribution problem.
2Length of moving object
If the configuration is made thinner to reduce device size, then the planar illumination device achieves compact form factor and lower profile, but uneven color becomes more conspicuous and illumination performance deteriorates
Solution Approach 1:
The second coverlay film serves as a compact intermediary layer that can be integrated into the thin-profile structure without significantly increasing overall device thickness. By placing this filtering layer strategically in the light path, the system maintains its compact form factor while effectively correcting the color uniformity issue that becomes more pronounced in thinner configurations.
3Area of stationary object
If light rays emitted at angles to the optical axis are allowed to pass through, then the planar illumination device achieves wide light distribution and improved illumination coverage, but yellow-tinted light increases and causes color non-uniformity
Solution Approach 1:
The second coverlay film applies a localized filtering function to different regions of the light output. It selectively targets and absorbs yellow-tinted rays in specific angular ranges while allowing other light rays to pass through. This local quality adjustment maintains wide illumination coverage by preserving overall light distribution while correcting color uniformity in the problematic angular regions.
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 absorption of yellow-tinted light by the second coverlay film reduces the occurrence of uneven color and enhances the luminance of the light emitting surface, allowing for a more efficient and thinner planar illumination device configuration.
Implementation Method 1
a second coverlay film and a second conductive layer stacked in sequence on a second surface of the base film, the second coverlay film including a light absorber
Data Source
AI summary
A planar illumination device includes: a light guide plate; a point light source disposed to face a light incident surface of the light guide plate; and a circuit substrate on which the point light source is mounted. The circuit substrate includes: a base film; a first conductive layer and a first coverlay film stacked in sequence on a first surface of the base film, the first conductive layer including a pair of lands to which a pair of electrode terminals of the point light source are electrically connected; and a second conductive layer and a second coverlay film stacked in sequence on a second surface of the base film the second coverlay film including a light absorber. The second coverlay film is exposed between the lands and in front of a light emitting surface of the point light source in a light emitting direction.