Phosphor-Converted Backlight for Wide-Gamut Display Brightness
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Solution Overview
Problem
Existing color image display devices face challenges in achieving high color purity and brightness due to inadequate emission from backlights, particularly with yellow-emitting phosphors, which lead to reduced color reproducibility and increased brightness at the expense of NTSC ratio, and the complexity of combining red, green, and blue LEDs for improved color reproduction.
Innovation Solution
A semiconductor light emitting device with specific phosphors, such as a green emitting phosphor with an emission peak in the 515-550 nm range and a red emitting phosphor with a narrow emission peak in the 610-650 nm range, combined with a blue or deep blue light source, to enhance light use efficiency and NTSC ratio without compromising brightness, allowing for broad color reproducibility and easy white balance adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If yellow-emitting phosphors are used in the backlight, then brightness is increased, but NTSC ratio and color reproducibility deteriorate
Solution Approach 1:
The patent segments the backlight emission into multiple wavelength regions by using a blue LED combined with multiple phosphors (yellow, orange, red) instead of a single yellow phosphor. This segmentation allows the color filter to extract pure red, green, and blue wavelengths, achieving high NTSC ratio while maintaining brightness through the combined phosphor emissions.
2Manufacturing precision
If the color filter is adjusted to increase NTSC ratio for vivid color reproduction, then color purity is improved, but screen brightness deteriorates
Solution Approach 1:
The patent changes the spectral parameters of the backlight by selecting specific phosphors with defined emission characteristics (yellow phosphor with 560-580nm peak, orange phosphor with 590-610nm peak, red phosphor with 620-650nm peak). This parameter optimization allows the color filter to achieve high NTSC ratio while the backlight provides sufficient brightness through its broad spectral coverage.
3Manufacturing precision
If red, green, and blue LEDs are combined to improve color reproduction, then color reproducibility is enhanced, but device complexity and mounting difficulty increase
Solution Approach 1:
The patent merges multiple phosphors (yellow, orange, red) onto a single blue LED chip, creating an integrated light source that provides broad spectral coverage. This combining approach achieves high color reproducibility equivalent to multiple LED combinations but with simpler mounting, as only one LED chip needs to be installed rather than three separate RGB LEDs.
4Device complexity
If a single blue LED with multiple phosphors is used, then device complexity is reduced and mounting is simplified, but achieving high NTSC ratio and brightness simultaneously becomes challenging
Solution Approach 1:
The patent uses a composite phosphor system combining yellow, orange, and red phosphors with the blue LED. This composite material approach creates a backlight with optimized spectral characteristics that simultaneously achieves high NTSC ratio, sufficient brightness, and simplified mounting, as the multiple phosphors work together to provide the necessary spectral coverage for vivid color reproduction.
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 enables high luminance and emission efficiency with improved durability, allowing for deep red and green reproduction without sacrificing image brightness, thus achieving broad color reproducibility and simplifying the mounting process by using a single chip for red, green, and blue emissions.
Implementation Method 1
A semiconductor light emitting device with specific phosphors, such as a green emitting phosphor with an emission peak in the 515-550 nm range and a red emitting phosphor with a narrow emission peak in the 610-650 nm range, combined with a blue or deep blue light source
Data Source
AI summary
To provide a semiconductor light emitting device which is capable of accomplishing a broad color reproducibility for an entire image without losing brightness of the entire image. A light source provided on a backlight for a color image display device has a semiconductor light emitting device comprising a solid light emitting device to emit light in a blue or deep blue region or in an ultraviolet region and phosphors, in combination. The phosphors comprise a green emitting phosphor and a red emitting phosphor. The green emitting phosphor and the red emitting phosphor are ones, of which the rate of change of the emission peak intensity at 100° C. to the emission intensity at 25° C., when the wavelength of the excitation light is 400 nm or 455 nm, is at most 40%.