White LED Phosphor Layering for Thermal Color Stability
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Solution Overview
Problem
White light emitting LEDs, particularly those using Chip on Board (COB) designs, face issues with low luminous efficacy and poor thermal stability due to the use of blue and red LED chips with different thermal characteristics, leading to color instability with temperature changes.
Innovation Solution
A white light emitting device is designed with first and second LEDs generating excitation light in the 440-480 nm range, covered by specific photoluminescence materials that convert blue light into red light, improving luminous efficacy and thermal stability by using a combination of a first photoluminescence material with a peak emission wavelength of 500-590 nm and a second material with a peak emission wavelength of 600-650 nm, applied in a configuration that enhances light uniformity and conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If COB white LED uses blue LED chips covered by red and green/yellow photoluminescence materials, then white light is generated, but luminous efficacy is low
Solution Approach 1:
The invention divides the white LED structure into separate red LED chips and blue LED chips rather than using a single blue chip with phosphor coating. This segmentation allows each chip type to operate at its optimal wavelength without the energy losses associated with phosphor conversion, thereby improving overall luminous efficacy while maintaining manufacturability through standardized chip mounting processes.
Solution Approach 2:
The invention combines red LED chips and blue LED chips in a composite structure to generate white light. By integrating multiple light sources with different spectral characteristics, the system achieves superior luminous efficacy compared to single-chip phosphor-converted LEDs, while the modular composite design facilitates manufacturing through independent chip optimization and assembly.
2Use of energy by moving object
If red LED chips are used without phosphor materials, then luminous efficacy is improved, but thermal stability is poor
Solution Approach 1:
The invention merges red LED chips and blue LED chips into a unified white LED system where both chip types contribute to the overall light output. This combination allows the red chips to operate without phosphor conversion (maintaining high efficacy) while the blue chips provide complementary wavelengths, and the integrated thermal management system stabilizes the color output across temperature variations.
Solution Approach 2:
The invention controls the drive currents and operating parameters of the red and blue LED chips to maintain color stability despite thermal variations. By dynamically adjusting electrical parameters and utilizing the complementary thermal characteristics of the two chip types, the system compensates for individual chip drift and maintains consistent white light output across temperature ranges.
3Use of energy by moving object
If blue and red LED chips are used together, then luminous efficacy is improved, but color stability with temperature changes deteriorates
Solution Approach 1:
The invention applies different thermal management strategies to the red and blue LED chips based on their specific thermal characteristics. Each chip type is positioned and thermally coupled to the heat sink with optimized contact areas and thermal pathways, allowing localized heat dissipation that maintains color stability while preserving the high efficacy benefits of direct-emission LED chips.
Solution Approach 2:
The invention incorporates thermal feedback mechanisms that monitor temperature variations and adjust the drive currents to red and blue LED chips accordingly. This active compensation maintains color stability by counteracting thermal drift effects, while the feedback control system is designed to minimize energy overhead and preserve overall luminous efficacy.
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 achieves improved luminous efficacy and thermal stability, providing a more efficient and color-stable white light emission across varying temperatures, with the ability to tune color temperature and reduce the amount of photoluminescence material required, enhancing manufacturing cost-effectiveness.
Implementation Method 1
a first photoluminescence material which generates light having a peak emission wavelength in a range from 500 nm to 590 nm; and a second photoluminescence material which generates light having a peak emission wavelength in a range from 600 nm to 650 nm
Data Source
AI summary
An exemplary method of manufacturing a white light emitting device may include providing first LEDs and second LEDs operable to generate excitation light having a dominant wavelength in a range from 440 nm to 480 nm; providing a first photoluminescence material which generates light having a peak emission wavelength in a range from 500 nm to 590 nm; providing a second photoluminescence material which generates light having a peak emission wavelength in a range from 600 nm to 650 nm; disposing the second photoluminescence material over and into direct contact with the second LED; and disposing the first photoluminescence material over the first and second LEDs.