Wavelength-Converted LED with Dichroic Filter for LCD Backlight
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Solution Overview
Problem
Conventional phosphor-converted LEDs for LCD backlighting provide a poor color gamut due to a lack of red light in the spectrum, resulting in a gamut that is only 69% as large as the NTSC standard.
Innovation Solution
Incorporating yellow/green and red phosphors, along with a filter layer that recycles and refocuses absorbed light, to enhance the color gamut by transmitting specific wavelengths and reflecting others, thereby improving the spectrum's coverage of the color space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional phosphor-converted LEDs are used for LCD backlighting, then the device structure remains simple, but the color gamut is poor (only 69% of NTSC standard) due to lack of red light in the spectrum
Solution Approach 1:
The patent segments the backlight system into multiple functional layers: a blue LED light source, a yellow phosphor layer, a red phosphor layer, and a dichroic filter layer. Each layer performs a specific function in generating or modifying the spectrum, allowing the system to achieve broad color gamut coverage (79-87% of NTSC standard) while maintaining reasonable structural organization
Solution Approach 2:
The dichroic filter layer acts as an intermediary component that selectively transmits blue and yellow light wavelengths while reflecting red light wavelengths back toward the phosphor layers. This mediator enables the recycling of red light that would otherwise be lost, significantly improving the red component of the spectrum and overall color gamut
2Manufacturing precision
If yellow and red phosphors are added to improve color gamut, then the spectrum coverage increases, but the device complexity increases due to additional layers and components
Solution Approach 1:
The patent combines multiple phosphor materials (yellow phosphor with peak emission around 560-580nm and red phosphor with peak emission around 610-650nm) with the blue LED source in a single integrated backlight structure. This merging of multiple light-generating components into one unified system achieves broad spectrum coverage (79-87% of NTSC standard) without requiring separate lighting modules
Solution Approach 2:
The dichroic filter layer recycles red light wavelengths that are initially absorbed or lost by reflecting them back toward the red phosphor layer for re-emission. This recovery mechanism improves the efficiency of red light generation and enhances the overall color gamut without requiring additional red light sources
3Manufacturing precision
If a filter layer is added to recycle and refocus absorbed light, then the color gamut increases to 79% or 87% of NTSC standard, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent utilizes the optical parameter properties of dichroic filter materials that exhibit wavelength-selective transmission and reflection characteristics. By selecting materials with specific optical parameters (transmitting blue and yellow wavelengths while reflecting red wavelengths), the system achieves enhanced color gamut (79-87% of NTSC standard) through material property optimization rather than complex structural design
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 increases the color gamut from 69% to 79% or 87% of the NTSC standard, depending on the phosphor combinations and filter configurations, enhancing the display's ability to produce a wider range of colors.
Implementation Method 1
Each pixel location is adapted to transmit light of the desired color and absorb light of the other two colors
Implementation Method 2
a first filter layer disposed between the at least one light source and the liquid crystal layer. The first filter layer includes a plurality of red pixel locations, green pixel locations, and blue pixel locations
Implementation Method 3
The second filter layer is adapted to transmit the red, green, and blue light transmitted by the first filter layer, and reflect light at a wavelength that is absorbed by the first filter layer
Implementation Method 4
a second filter layer disposed between first filter layer and the light source. The second filter layer is adapted to transmit the red, green, and blue light transmitted by the first filter layer, and reflect light at a wavelength that is absorbed by the first filter layer
Implementation Method 5
Semiconductor light emitting devices such as light emitting diodes (LEDs) are among the most efficient light sources currently available
Implementation Method 6
a light source including a semiconductor light emitting device
Implementation Method 7
Incorporating yellow/green and red phosphors, along with a filter layer that recycles and refocuses absorbed light
Data Source
Figure 1~3
Figure 4~6
Figure 7~9
AI summary
A semiconductor light emitting device (34) comprises a light emitting layer disposed between an n-type region and a p-type region. The light emitting layer is adapted to emit first light having a first peak wavelength. A first wavelength converting material (38) is adapted to absorb the first light and emit second light having a second peak wavelength. A second wavelength converting material (36) is adapted to absorb either the first light or the second light and emit third light having a third peak wavelength. A filter (40) is adapted to reflect fourth light having a fourth peak wavelength. The fourth light is either a portion of the second light or a portion of the third light. The filter is configured to transmit light having a peak wavelength longer or shorter than the fourth peak wavelength. The filter is disposed over the light emitting device in the path of at least a portion of the first, second, and third light.