Chromaticity Rank Determination for Light Emitting Devices
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Solution Overview
Problem
White LEDs of the same chromaticity rank can have varying light emission spectra, leading to significant chromaticity variations after passing through a color filter in liquid crystal display devices, which can result in chromaticity being outside a predetermined range.
Innovation Solution
A method for determining the chromaticity rank of a light emitting device by selecting a combination of blue, green, and red light emitting elements or fluorescent members with specific peak wavelengths and ratios, ensuring the chromaticity of the light emitted falls within a predetermined range on the 1931 CIE Chromaticity Diagram, thereby reducing chromaticity variations after passing through a color filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If white LEDs of the same chromaticity rank are selected based on conventional chromaticity diagrams, then the chromaticity point appears to be within the desired range, but the light emission spectra vary significantly causing chromaticity variations after passing through color filters to fall outside the predetermined range
Solution Approach 1:
The patent changes the parameters used for chromaticity ranking from conventional CIE chromaticity coordinates (x, y) to a new parameter system based on spectral characteristics. Specifically, it uses the peak wavelengths of blue (447-452 nm), green (520-541 nm), and red (630-632 nm) light emitting elements, along with their luminance ratios, to define chromaticity ranks. This parameter transformation ensures that LEDs with the same chromaticity rank have consistent spectral characteristics that maintain uniform chromaticity after passing through color filters.
2Adaptability or versatility
If a wide range of blue LED peak wavelengths (440-455 nm) is used to achieve desired white LED chromaticity, then chromaticity points overlap on the chromaticity diagram, but the resulting light emission spectra cause significant chromaticity variations after color filter transmission
Solution Approach 1:
The patent applies local quality by specifying precise wavelength ranges for each color component: blue light emitting elements with peak wavelengths of 447-452 nm, green light emitting elements with peak wavelengths of 520-541 nm, and red light emitting elements or fluorescent members with peak wavelengths of 630-632 nm. By controlling the spectral characteristics of each individual component rather than relying on overall chromaticity, the patent ensures uniform chromaticity output after color filter transmission while maintaining manufacturing precision.
3Ease of manufacture
If conventional chromaticity ranking methods are used without considering spectral characteristics, then the selection process is simple, but the chromaticity of light after passing through color filters varies significantly and may fall outside predetermined ranges
Solution Approach 1:
The patent implements preliminary action by pre-defining chromaticity ranks based on spectral characteristics before the actual LED selection process. The method establishes specific wavelength ranges and luminance ratio requirements for blue, green, and red components in advance. During manufacturing, LEDs are simply categorized into predefined chromaticity ranks by measuring their spectral parameters, which simplifies the selection process while ensuring accurate chromaticity control after color filter transmission.
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 approach ensures that the chromaticity of the light emitted from the light emitting device remains within a predetermined range, reducing the need for color filter adjustments and maintaining uniform luminance and color reproducibility.
Implementation Method 1
a blue LED die and a wavelength conversion member (fluorescent material), which absorbs blue light from the blue LED die and converts the wavelength of the light into a different wavelength
Implementation Method 2
a fluorescent material that is adapted to emit yellow fluorescent light upon excitation by respective blue LED die
Data Source
AI summary
A method of determining a chromaticity rank of a light emitting device includes selecting the light emitting device having a chromaticity rank in a region surrounded by four defining points on a 1931 CIE Chromaticity Diagram. A ratio of a distance in a y-direction between, of the four defining points, two defining points furthest from each other in the y-direction to a distance in an x-direction between, of the four defining points, two defining points furthest from each other in the x-direction is 0.5 or less A peak light emission wavelength of the blue light emitting element is in a range of 447 to 452 nm, a peak light emission wavelength of the green light emitting element is in a range of 520 to 541 nm, and a peak light emission wavelength of the red light emitting element is in a range of 630 to 632 nm.