Introduction
LEDs are favored for their technical, economic, ecological, and design benefits over traditional lighting. However, they face challenges such as color and intensity changes due to aging, current, and temperature variations. These changes can be managed using color sensors.

Functionality of Color Sensors
Color sensors typically use the three-range method with RGB or other spectral filters. MAZeT's sensors mimic the CIE 1931 standard spectral value function of the human eye, offering a cost-effective alternative to spectrometers for light measurement and regulation. Key characteristics of absorption and interference filters are detailed in tables.

Calibration
Calibration of color sensors involves a correction matrix and is sufficient with the primary colors of a multicolor LED, though adding white improves regulation. The process includes measuring target colors with both a color sensor and a spectrometer.

Color Sensors in LED Systems
An example with an MTCSiCS True Color Sensor and RGB LEDs highlights the integration requirements for LED systems, such as focusing on a homogeneously illuminated surface and adjusting sensor voltages to the temperature range. The MTCSiCS sensor, paired with the MTI04 amplifier, supports both PWM and constant current control methods.

Conclusion
True Color Sensors ensure consistent color in LED systems despite temperature, aging, and current variations. Successful integration requires attention to system requirements and calibration.

Improvement of Color Stability
This section discusses compensating for color changes in RGB LEDs due to temperature fluctuations using a color sensor. An RGB LED backlight system is enhanced with the MTCS-C2 Colorimeter board, featuring a True Color Sensor, amplifier, and microcontroller. Tests involve cooling and heating the LED's heatsink from 0°C to 70°C across three runs: without regulation, with RGB sensor regulation, and with True Color Sensor regulation.

Test Results

• Run 1 (No Regulation): Significant color shift with a 7.5% brightness change and a color shift of 0.0332.
• Run 2 (RGB Sensor Regulation): Reduced color shift with a 1.0% brightness change and a color shift of 0.0227.
• Run 3 (True Color Sensor Regulation): Minimal color shift with a 0.3% brightness change and a color shift of 0.0028, within the human eye's indistinguishable range.

Summary
Regulation of multi-colored LEDs is crucial for applications requiring consistent color. Unregulated systems show unacceptable color changes with temperature variations. RGB sensors reduce changes but remain above acceptable thresholds. True Color Sensors provide successful regulation, achieving results indistinguishable to the human eye.

Author:
Name: Dipl.-Ing. (FH) Fredrik Hailer
Education: Mechatronics (Karlsruhe University of Applied Sciences)
Employer: MAZeT GmbH (Jena) since April 2007 as a Field Application Engineer in Color and Spectral Sensor Technology.