LED Illumination Device with Photodetector Feedback for Aging Compensation
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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 varying effects of temperature and aging on different LED colors, and inadequate compensation methods.
Innovation Solution
The implementation of a method and device that utilize a plurality of LEDs, photodetectors, and a control circuit to continuously measure and adjust drive currents based on interpolation techniques and stored calibration values, ensuring accurate luminous flux and chromaticity maintenance by accounting for temperature and aging effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multi-colored LEDs are combined to produce white light with adjustable color temperature, then the versatility and lighting effects are improved, but the output characteristics (luminous flux and chromaticity) vary significantly over temperature and time
Solution Approach 1:
The patent divides the illumination device into multiple independently controllable LED channels (e.g., warm white LEDs, cool white LEDs, or RGB LEDs) and measures each channel's output characteristics separately using photodetectors. This segmentation allows individual compensation of each LED's aging and temperature effects, resolving the contradiction by maintaining overall stability while preserving color adjustment versatility.
Solution Approach 2:
The patent implements a feedback control system where photodetectors continuously measure the actual luminous flux and chromaticity output of each LED channel, and the control circuit adjusts drive currents in real-time to compensate for deviations. This closed-loop feedback maintains reliable and stable output characteristics while allowing wide color temperature adjustment range.
2Reliability
If drive currents are adjusted to compensate for LED aging and temperature effects, then the luminous flux and chromaticity stability are improved, but the device complexity increases due to multiple photodetectors and control circuits
Solution Approach 1:
The patent uses photodetectors that can detect multiple wavelengths simultaneously and a control circuit that processes compensation for both luminous flux and chromaticity together. This multi-functional approach reduces the number of separate components needed, achieving stable output characteristics without proportionally increasing device complexity.
Solution Approach 2:
The patent combines multiple photodetectors into a single integrated detection system and merges the control functions for different LED channels into one control circuit. This consolidation achieves the required compensation functionality while minimizing the increase in device complexity.
3Measurement precision
If individual LED chains are measured and compensated separately, then the measurement precision and compensation accuracy are improved, but the productivity decreases due to periodic shutdowns for measurements
Solution Approach 1:
The patent implements periodic measurement cycles where LED chains are briefly turned off for measurement, then quickly restored to operation. This periodic action allows accurate measurements to be taken without permanently interrupting illumination, resolving the contradiction by maintaining measurement precision while minimizing productivity loss through rapid switching.
Solution Approach 2:
The patent maintains continuous illumination by using multiple LED chains that can be measured and compensated in sequence, ensuring that when one chain is shut down for measurement, others continue to provide light. This approach preserves measurement precision while maintaining continuous useful action and productivity.
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 effectively maintains consistent luminous flux and chromaticity across temperature variations and the lifespan of LEDs, improving the accuracy and reliability of LED illumination devices.
Implementation Method 1
measuring a photocurrent induced on the photodetector in response to the illumination produced by each LED chain
Implementation Method 2
a plurality of light emitting diode (LED) chains generally configured to produce illumination for the illumination device
Data Source
AI summary
An illumination device and method is provided herein for controlling individual light emitting diodes (LEDs) in an LED illumination device, so that a desired luminous flux and a desired chromaticity of the device can be maintained over time as the LEDs age. According to one embodiment, the method comprises applying drive currents to a plurality of LED chains substantially continuously to produce illumination, measuring a photocurrent induced on the photodetector in response to the illumination produced by each LED chain, one LED chain at a time, and received by the photodetector, and measuring a forward voltage developed across the photodetector by applying a non-operative drive current to the photodetector. For each LED chain, the method may further comprise determining an expected photocurrent value corresponding to the forward voltage measured across the photodetector and the drive current currently applied to the LED chain by applying one or more interpolation techniques to a table of stored calibration values correlating forward voltage and photocurrent to drive current at a plurality of different temperatures, and adjusting the drive current currently applied to the LED chain if a difference exists between the expected photocurrent value and the measured photocurrent.