Warm White LED Luminophoric Medium for High CRI
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Solution Overview
Problem
Conventional light emitting diodes (LEDs) have limited color rendering index (CRI) values, failing to accurately reproduce a wide range of colors, especially in white light applications, due to their narrow wavelength distribution and lack of contribution from various visible wavelengths.
Innovation Solution
Incorporating a recipient luminophoric medium with specific phosphors, such as LuAG:Ce, YAG:Ce, and (Ca1-xSrx)SiAlN3:Eu2+, that down-convert blue light emitted by LEDs to radiation in the green, yellow, and red color ranges, extending the full width half maximum emission bandwidth into the cyan range, thereby enhancing the CRI and achieving warm white light with a correlated color temperature between 2500K and 3300K.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional LEDs are used to generate white light, then the device structure is simple, but the color rendering index is poor and spectral coverage is limited
Solution Approach 1:
The patent uses composite phosphor materials including green phosphor (β-SiAlON:Eu2+), red phosphor (CaAlSiN3:Eu2+), and yellow phosphor (YAG:Ce3+) to create a luminophoric medium that converts blue LED light into a broad spectrum white light with improved color rendering. This composite approach allows achieving high CRI without changing the simple LED device structure.
2Manufacturing precision
If multiple phosphors are added to improve CRI, then color rendering improves, but device complexity increases
Solution Approach 1:
The patent optimizes the weight ratios of different phosphors in the luminophoric medium to achieve the desired spectral characteristics. By adjusting parameters such as the ratio of green to red phosphor and the concentration of each phosphor, the system achieves high CRI while maintaining a manageable device structure.
3Manufacturing precision
If phosphor down-conversion is used to extend spectral coverage, then CRI improves, but luminous flux may be reduced
Solution Approach 1:
The patent selects phosphors with specific emission characteristics tailored to fill spectral gaps. The green phosphor with peak emission at 480-500nm specifically targets the cyan-green region, while the red phosphor covers 600-680nm, creating localized spectral enhancement that improves CRI without excessive luminous flux loss.
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 significantly increases the CRI values of LEDs to above 90, providing warm white light with improved color accuracy and a broader spectral coverage, while maintaining a high luminous flux, thus addressing the limitations of monochromatic LEDs in general illumination applications.
Implementation Method 1
a first phosphor that down-converts the light emitted by the LED to light having a peak wavelength in the green color range that has a full width half maximum bandwidth that extends into the cyan color range
Implementation Method 2
a first phosphor that down-converts the light emitted by the LED to light having a peak wavelength in the green color range
Data Source
AI summary
Light emitting devices include a solid state lighting source and a recipient luminophoric medium for down-converting at least some of the radiation emitted by the solid state lighting source. The recipient luminophoric medium includes a first material that down-converts the radiation emitted by the solid state lighting source to radiation having a peak wavelength in the green color range that has a full width half maximum emission bandwidth that extends into the cyan color range, and at least one additional material that down-converts the radiation emitted by the solid state lighting source to radiation having a peak wavelength in another color range.