How to maintain color levels of LED light sources within cars

October 19, 2011 // By Frank Krumbein, MAZeT
Light emitting diodes are perfect for lighting purposes within cars. But the side effects of LED light is that the wave length changes with the ambient temperature, the intensity loses its strength over time, and age-related darkening of the lenses can additionally alter colors. This article explains how color levels of LED light sources can be maintained through appropriate color sensors and intelligent lighting control.

The usage of LEDs within the display and illumination technology is drastically increasing. The determinant factors for this development are not only the reduced size of the components, but decisively the increased life-cycle, lower energy consumption, increased performance, and broad range of color usage (color gamut).

By combining RGBx-LEDS (x = extension of RGB with additional LEDs colored amber and white) within a light source, it is possible to generate any color or color temperature, which are defined by the limitations of the single LEDS within the color gamut. Therefore it is possible for illumination engineering to simulate daylight, individual ambient lighting, other visual effects, and color temperatures.

Many factors affect the light color

The emitted spectrum of a LED depends on various factors. Especially variations within operating temperature, production tolerances, diode currents, life cycle of LEDs as well as tolerances of driver electronics can alter the lighting characteristics drastically. Brightness and colors are affected during operation, hence to environmental influence such as temperature fluctuation.

Active controlling allows maintaining constant LED lighting

How is it possible to maintain constant lighting and color impression for lamps, lights or back lights over a long period of time? This is especially important for a luminary setup of multiple RGBx light sources.

To maintain constant color impression and brightness over a full lifecycle of a RGBW-LED it is necessary to have an active control of the color area and perform a targeted mix of the LED color range. Simple, inexpensive, long-term and temperature stable sensors are essential to measure the color area of specific LED sources. Therefore the sensor may not change its characteristics over the lifetime of the LED. Sensors that lose their characteristics after some hundred hours operating time are unsuitable.

Nominal/actual value comparison provides correction signal

The nominal value of the color area is send from the sensor to the management settings and generates a corrected control pulse after the comparison.

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