White LED Chromaticity Balancing for Lifetime Color Stability
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Solution Overview
Problem
Phosphor-based white LEDs experience significant color shifts over their lifetime, which can lead to undesirable changes in the emitted light, affecting applications where color stability is crucial, such as retail, museums, healthcare, and industrial settings, as human sensitivity to color changes is higher than light intensity changes.
Innovation Solution
A system comprising two or more phosphor-containing white LEDs selected to minimize combined color shift over extended periods, using a Differential Chromaticity Algorithm (DCA) model to predict and manage color shifts, and employing phosphor stabilization means like anisotropic particles and cross-linked polymer networks to reduce color variation, along with current varying mechanisms to adjust brightness based on sensor feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphor-based white LEDs are used for broadband visible illumination, then illumination coverage and energy efficiency are improved, but color stability deteriorates over time due to chromaticity shift
Solution Approach 1:
The patent segments the single LED light source into multiple LEDs with different chromaticity characteristics. By combining multiple LEDs (e.g., some with initial chromaticity above specification and some below), the system achieves both energy efficiency of LEDs and improved color stability through complementary aging behaviors that cancel each other's chromaticity shifts.
Solution Approach 2:
The patent changes the parameters of the lighting system by selecting LEDs with specific initial chromaticity values that differ from the standard specification. LEDs are deliberately chosen with chromaticity coordinates above or below the specified range, and their operating currents are adjusted to achieve the desired combined chromaticity while accounting for their different aging rates and color shift patterns.
2Stability of the object's composition
If multiple LEDs with different chromaticity characteristics are combined, then color stability is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple LEDs with different chromaticity characteristics into a single lighting system that outputs combined light. The LEDs are positioned to illuminate the same area, and their outputs are optically combined, creating a unified light source with stabilized chromaticity properties while maintaining relative system simplicity.
Solution Approach 2:
The system utilizes the natural aging characteristics of different LEDs to self-regulate color stability. LEDs with initial chromaticity above specification tend to shift downward over time, while those below specification shift upward, creating a self-compensating mechanism that maintains color stability without requiring active control systems or complex monitoring.
3Manufacturing precision
If LEDs are selected based on initial chromaticity specifications, then manufacturing precision is maintained, but long-term color stability is compromised due to unaccounted aging variations
Solution Approach 1:
The patent applies preliminary action by pre-selecting LEDs with specific chromaticity characteristics before assembly, rather than relying solely on standard specification compliance. LEDs are deliberately chosen with chromaticity values above or below the standard range, and their expected aging patterns are calculated in advance to ensure that their combined output will maintain stable chromaticity throughout their operational lifetime.
Solution Approach 2:
The system incorporates feedback mechanisms by measuring and calculating the combined chromaticity output of multiple LEDs and adjusting individual LED operating currents accordingly. This feedback loop ensures that the combined output maintains the desired chromaticity specification while accounting for the different aging rates and color shift patterns of individual LEDs.
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 system achieves reduced color shift, ensuring stable light output and extended color stability, allowing for accurate prediction and compensation of color changes, thereby enhancing LED performance and reliability in color-critical applications.
Implementation Method 1
A portion of the light emitted from the LED die is converted to longer wavelength light by the phosphor
Implementation Method 2
phosphor stabilization means like anisotropic particles and cross-linked polymer networks to reduce color variation
Data Source
AI summary
A system includes two or more phosphor-containing white LEDs (or other color-shifting artificial light sources) selected so that their combined color shift over at least 8,000 hours (e.g., at least 10,000 hours, at least 20,000 hours, at least 30,000 hours, at least 40,000 hours, up to 200,000 hours, up to 100,000 hours, up to 80,000 hours) of operation is less than at least one of the LED's (or the other color-shifting artificial light source's) color shift over that time. Here, the combined color shift (Δu′v′) over the at least 8,000 hours (e.g., at least 10,000 hours, at least 20,000 hours, at least 30,000 hours, at least 40,000 hours, up to 200,000 hours, up to 100,000 hours, up to 80,000 hours) of operation can be less than 0.007 (e.g., 0.006 or less, 0.005 or less, 0.004 or less, 0.003 or less, 0.002 or less, 0.001 or less, 0.0005 or less).