LED Lumen Maintenance via Laser-Calibrated Photodetector Feedback
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Solution Overview
Problem
Solid state light sources, such as LEDs, experience lumen depreciation over time, making it challenging to maintain consistent light output and color stability, especially in applications where color mixing is involved, as traditional methods do not account for individual LED characteristics and photodiode degradation.
Innovation Solution
A lighting assembly is configured with a diffusible light source, a photo detector, and a directed light source, like a laser, which provides a 'golden sample' for calibration. The system measures baseline and subsequent lumen output to determine photodiode degradation, allowing for real-time compensation through adjusted drive signals to maintain consistent lumen output and color stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional light sources (incandescent, halogen) are used, then they burn out before substantial loss of light output occurs, but they have shorter lifetime and higher power consumption compared to LEDs
Solution Approach 1:
The patent implements a feedback mechanism where a photodetector continuously monitors the light output of the LED. The measured lumen output is fed back to a controller that adjusts the drive current to compensate for lumen depreciation, thereby maintaining consistent light output over the extended lifetime of the LED.
Solution Approach 2:
The system performs self-calibration using a directed light source as a reference. The photodetector measures the reference light source to determine its own degradation characteristics, and this self-determined calibration factor is applied to correct subsequent measurements of the illumination light source, enabling the system to maintain accuracy without external intervention.
2Duration of action of moving object
If LEDs are used for long lifetime operation, then they maintain operation for extended periods, but lumen output degrades continuously over time
Solution Approach 1:
The system continuously monitors LED lumen output through a photodetector and feeds this information back to a controller. The controller adjusts the drive current in real-time to compensate for lumen depreciation, ensuring the LED maintains its rated lumen output throughout its extended operational lifetime.
Solution Approach 2:
The patent dynamically changes the electrical parameters (drive current, voltage) of the LED based on measured lumen output. By adjusting these parameters in response to degradation, the system compensates for lumen depreciation and maintains consistent illumination intensity over time.
3Measurement precision
If photodetector is used to measure lumen output over time, then lumen depreciation can be monitored, but the photodetector itself degrades causing measurement errors
Solution Approach 1:
The photodetector performs self-calibration by measuring a directed reference light source with known stable output. By comparing its measurements of the reference source against expected values, the photodetector determines its own degradation characteristics and calculates a calibration factor that it applies to subsequent measurements, thereby maintaining measurement accuracy despite its own degradation.
Solution Approach 2:
The directed reference light source acts as an intermediary standard. The photodetector uses this reference source as a mediator to calibrate its response characteristics. The reference source provides a stable benchmark that allows the photodetector to characterize and compensate for its own degradation without requiring external calibration equipment.
4Adaptability or versatility
If color mixing of multiple lumen outputs is used, then diverse lighting applications are enabled, but color stability becomes difficult to maintain due to differential lumen depreciation
Solution Approach 1:
The system implements separate feedback control loops for each LED chip contributing to the color mix. Each chip's lumen output is monitored independently, and drive currents are adjusted individually to compensate for differential lumen depreciation, thereby maintaining the intended color mixture and stability over time.
Solution Approach 2:
The patent dynamically adjusts the electrical parameters (current, voltage) of individual LED chips in a color-mixing array. By changing these parameters in response to measured lumen output from each chip, the system compensates for differential degradation rates and maintains stable color composition throughout the lifetime of the lighting assembly.
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 minimizes measurement errors due to photodiode degradation, enabling accurate lumen output maintenance and color stability over the lifetime of the lighting assembly, suitable for various light sources, including LEDs and other solid state light sources.
Implementation Method 1
a directed light source to provide a golden sample light beam
Implementation Method 2
a photo detector configured to measure lumen output of the diffusible light source and a golden sample light beam
Data Source
AI summary
Techniques are disclosed for maintaining consistent lumen output of a lighting assembly over time. By maintaining a consistent lumen output, it is possible to maintain acceptable color stability where color mixing of multiple outputs is used. The lighting assembly may be any lighting configuration that might suffer from lumen depreciation and/or color drift over time, and may include any type(s) of light source(s) that may be monitored and driven accordingly. The lighting assembly, in addition to light source(s), includes a photo detector and a directed light source, such as a laser. The directed light source provides a golden sample for use in calibrating the photo detector, which in turn monitors lumen output of the light source(s). Drive signals are adjusted to account for lumen depreciation of the monitored light source(s).