Phosphor Mixture for High Color Rendering White LEDs
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Solution Overview
Problem
Conventional white LED lighting units suffer from inadequate luminance and poor color rendering properties, particularly at correlated color temperatures of 4500K or less, due to insufficient red emission components, leading to dull and bluish white light.
Innovation Solution
A phosphor mixture comprising a red phosphor with an emission spectrum peak in the 630-680 nm range and an excitation band from ultraviolet to visible light, combined with other phosphors, to enhance luminance and color rendering properties across a wide range of correlated color temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional blue LED and yellow phosphor are combined to produce white light, then the structure is simple and manufacturing is easy, but the color rendering properties are deteriorated and red emission component is insufficient
Solution Approach 1:
The patent uses a composite phosphor system combining yellow phosphor (Y3Al5O12:Ce) and red phosphor (CaAlSiN3:Eu) to create a phosphor mixture that emits both yellow and red light when excited by blue LED. This composite approach maintains manufacturing simplicity while significantly improving color rendering properties by providing sufficient red emission component (R9≥60) that was missing in conventional single-phosphor systems.
2Manufacturing precision
If red phosphor quantity is increased to improve color rendering properties, then the color rendering index is improved, but the luminance is reduced and the light appears darker
Solution Approach 1:
The patent optimizes the excitation wavelength parameter of the blue LED to 430-500 nm, which matches the absorption characteristics of both yellow and red phosphors. This parameter optimization enables simultaneous efficient excitation of both phosphors, achieving high luminance (luminous efficacy ≥30 lm/W) and good color rendering (Ra≥80, R9≥60) without the need to increase red phosphor quantity excessively.
Solution Approach 2:
The patent assigns different functions to different phosphors in the composite system: yellow phosphor (Y3Al5O12:Ce) provides high-luminance yellow emission for brightness, while red phosphor (CaAlSiN3:Eu) provides red emission for color rendering. This functional differentiation allows each phosphor to operate at optimal efficiency, maintaining high luminance while achieving excellent color rendering properties.
3Manufacturing precision
If multiple phosphors are combined to improve color rendering properties, then the emission spectrum is enhanced, but the device complexity is increased
Solution Approach 1:
The patent creates a composite phosphor material system using two well-established phosphors (Y3Al5O12:Ce and CaAlSiN3:Eu) that can be mixed and applied together on the blue LED chip. This approach enhances the emission spectrum to cover yellow and red regions while maintaining relatively simple device structure and manufacturing process, avoiding the complexity of multi-LED combinations or complex optical systems.
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 phosphor mixture achieves sufficient luminance and excellent color rendering properties, even at low correlated color temperatures, by providing a continuous emission spectrum with multiple peaks and improved red emission, resulting in brighter and more natural-looking light.
Implementation Method 1
a phosphor mixture comprising a red phosphor with an emission spectrum peak in the 630-680 nm range and an excitation band from ultraviolet to visible light
Data Source
AI summary
To provide a light emitting device having a phosphor mixture and a light emitting part, the phosphor mixture including a red phosphor and more than one kind of phosphor having an emission spectrum with a peak in a wavelength range from 500 nm to 630 nm, and emitting light having a sufficient luminance and excellent in color rendering properties not only in a white light with high correlated color temperature, but also in a warm white light with low correlated color temperature. CaAlSiN3:Eu manufactured as a red phosphor and and CaAl2Si4N8:Eu manufactured as an orange phosphor, and for example, commercial YAG:Ce as a yellow-green phosphor, are prepared, and emission spectra of these phosphors are measured when excited by excitation light in the wavelength range from 430 nm to 500 nm. Further, the emission spectrum of the light used as an excitation light are measured, by simulation using their emission spectra, a mixing ratio of each phosphor, by which the correlated color temperature of the phosphor mixture becomes a target color temperature, is obtained. And based on the result of the simulation, each phosphor is measured and mixed, thus obtaining the phosphor mixture.