Phosphor-Converted White LED Thermal Red-Shift Compensation
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Solution Overview
Problem
LED lighting faces issues with color shift and decreased efficiency due to thermal effects, leading to unstable correlated color temperature and color coordinates over time, as phosphors age and change the ratio of blue to yellow light.
Innovation Solution
A blue LED chip with an emission spectrum peak wavelength slightly smaller than the yellow phosphor's excitation spectrum peak wavelength, which red-shifts to match the phosphor's excitation spectrum as temperature increases, maintaining excitation ability and emission output power, thus stabilizing correlated color temperature and color coordinates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a blue LED chip with peak wavelength matching the phosphor's excitation spectrum is used, then excitation efficiency is improved, but thermal effects cause color shift and correlated color temperature instability over time
Solution Approach 1:
The patent applies preliminary action by intentionally selecting a blue LED chip whose peak emission wavelength is slightly smaller (blue-shifted) than the phosphor's excitation spectrum peak at room temperature. This preliminary mismatch compensates for the thermal red-shift that occurs during operation, ensuring that at elevated temperatures the LED's emission spectrum aligns with the phosphor's excitation spectrum, thereby maintaining stable correlated color temperature and color coordinates over time.
2Stability of the object's composition
If the LED chip emission spectrum is red-shifted to match the phosphor's excitation spectrum at elevated temperatures, then color stability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies parameter changes by deliberately selecting LED chips with specific peak wavelengths that are slightly smaller than the phosphor's excitation spectrum peak at room temperature. This parameter selection accounts for the thermal red-shift effect, ensuring that at operating temperatures the LED emission spectrum matches the phosphor excitation spectrum. This approach transforms a dynamic thermal stability problem into a static manufacturing specification, simplifying quality control.
3Stability of the object's composition
If optical and thermal feedback circuits are used to maintain chromaticity, then color stability is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates the need for complex optical and thermal feedback or feed-forward circuits by incorporating the thermal compensation function directly into the LED chip-phosphor pairing design. By selecting LED chips with peak wavelengths slightly smaller than the phosphor's excitation spectrum peak at room temperature, the system passively compensates for thermal effects through the natural red-shift phenomenon, achieving chromaticity stability without additional active control components.
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 effectively maintains stable correlated color temperature and color coordinates by ensuring the LED chip's emission spectrum aligns with the phosphor's excitation spectrum at elevated temperatures, reducing color drift and maintaining light efficiency.
Implementation Method 1
The blue LED chip emits light with an emission spectrum having a peak wavelength X
Implementation Method 2
the LED chip has its emission spectrum red-shifted to substantially match with the excitation spectrum of the phosphor
Implementation Method 3
The yellow phosphor has an excitation spectrum with a peak wavelength Y and is configured to convert part of light emitted from the LED chip
Implementation Method 4
the phosphor decays due to thermal effect, and the LED chip has its emission spectrum red-shifted to substantially match with the excitation spectrum of the phosphor
Data Source
AI summary
A light emitting device is provided to produce white light with a stable correlated color temperature and stable color coordinates. The light emitting device includes a blue LED chip and a yellow phosphor. The blue LED chip has a peak wavelength X slightly smaller than the peak wavelength Y of the phosphor such that when the light emitting device is subjected to a predetermined operating current, the phosphor decays due to thermal effect, and the LED chip has its emission spectrum red-shifted to substantially match with the excitation spectrum of the phosphor. At this time, the excitation ability of the LED chip is increased and causes an increase of yellow power output from the phosphor that substantially compensates a decrease of yellow light output caused by the phosphor.