Methods to measure the luminous color of white and colored LEDs

Uncertainty of different methods to measure the luminous color of white and colored LEDs used for exterior automotive lighting

Hassan Gargouri, Oliver Esterl, Dominique Tribes, Steffen Lau, Martin Senft and Michael Breit

Instrument Systems Optische Messtechnik GmbH | Business Unit Lab Equipment | Optronik Line | Kaiserin-Augusta-Allee 16 - 24, 10553 Berlin, Germany

Exterior automotive lighting has developed rapidly from halogen lamps, to xenon lamps, to full light emitting diodes (LEDs) and laser diode headlamps and modules. The high efficiency, as well as their styling possibilities and innovative potential for ADB and Matrix beam solutions make LED technique very attractive as luminous and signal sources in vehicles. In addition, LEDs are extremely vibration-resistant, offer a long lifetime and low energy consumption and are therefore key technology for the pioneering electric mobility.

Due to the high requirements to fulfill the different standards in the automotive lighting sector, LEDs have to be precisely characterized regarding the different properties of the light. The light color is one of the most important properties in automotive lighting. White point tuning and color stability up to a predefined distance are an essential part of quality control. In fact, there are two different measurement principles to define the color of the light: tristimulus with a colorimeter and spectral with a spectrometer. While both methods offer an accurate measurement result of light color, they do it in different ways. In this presentation, we will explain the technique behind the two-measurement methods and will present the result deviation using white, blue, green and red LEDs. In addition, the deviation of the defined color coordinates CIE-x and CIE-y at different distances with both measurement methods will be shown.