Phosphor Converted LED Calibration Using Dual Photodetectors
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Solution Overview
Problem
Existing illumination devices using LEDs struggle to accurately maintain desired luminous flux and chromaticity over changes in temperature and time, particularly in multi-colored LED devices, due to variations in drive current and aging effects, which leads to inconsistent color output and reduced performance.
Innovation Solution
The implementation of a calibration method using two photodetectors to measure separate spectral portions of a phosphor converted LED, along with a control circuit to adjust drive currents based on measured photocurrents and forward voltages, allows for precise calibration and compensation to maintain desired luminous flux and chromaticity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If LED drive current is increased to maintain luminous flux, then brightness is improved, but chromaticity stability deteriorates due to temperature and aging effects
Solution Approach 1:
The patent implements feedback control by measuring the actual luminous flux and chromaticity of the LED illumination device using photodetectors, comparing these measurements to target values, and adjusting the drive currents to different colored LEDs accordingly. This closed-loop feedback system compensates for temperature and aging effects, maintaining stable chromaticity while preserving luminous flux output.
Solution Approach 2:
The patent changes operational parameters by adjusting the drive currents to individual colored LEDs based on measured temperature and aging conditions. The system modifies current distribution dynamically to compensate for spectral shifts, allowing the illumination device to maintain target chromaticity coordinates while preserving overall luminous flux through parameter optimization.
2Measurement precision
If multiple photodetectors are used to measure separate spectral portions, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent segments the spectral measurement function by using multiple photodetectors, each dedicated to detecting specific wavelength ranges corresponding to different colored LEDs. This segmentation allows precise measurement of each spectral portion independently, improving overall measurement accuracy while enabling separate calibration and control of each LED channel.
Solution Approach 2:
The patent makes the photodetector system multi-functional by having the same set of photodetectors serve dual purposes: measuring both luminous flux and chromaticity parameters, and providing data for both calibration and real-time control operations. This universality reduces overall system complexity despite using multiple detectors.
3Reliability
If calibration values are stored for multiple temperatures and drive currents, then compensation accuracy is improved, but memory requirements and processing complexity increase
Solution Approach 1:
The patent performs preliminary calibration actions by pre-measuring and storing calibration values for luminous flux and chromaticity at multiple predetermined temperatures and drive current combinations during manufacturing. This preliminary action creates a lookup table that enables fast, accurate compensation during operation without requiring complex real-time calculations, balancing accuracy with processing simplicity.
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
This approach ensures accurate and consistent color output and luminous flux over temperature changes and the lifespan of the LEDs, effectively addressing the limitations of prior art by individually calibrating and compensating each LED within the illumination device.
Implementation Method 1
measuring photocurrents, which are induced on the first and second photodetectors by illumination produced by the phosphor converted LED
Implementation Method 2
an illumination device comprising a phosphor converted LED
Data Source
AI summary
An illumination device described herein includes at least a phosphor converted LED, which is configured for emitting illumination for the illumination device, a first photodetector and a second photodetector. A spectrum of the illumination emitted from the phosphor converted LED comprises a first portion having a first peak emission wavelength and a second portion having a second peak emission wavelength, which differs from the first peak emission wavelength. The first photodetector has a detection range, which is configured for detecting only the first portion of the spectrum emitted by the phosphor converted LED. The second photodetector has a detection range, which is configured for detecting only the second portion of the spectrum emitted by the phosphor converted LED. Methods are provided herein for calibrating and controlling each portion of the phosphor converted LED spectrum, as if the phosphor converted LED were two separate LEDs.