Determination of interior surface temperature using luminance measurement of thermochromic liquid crystals

This paper presents a new method to measure interior surface temperature distributions. An image-resolved luminance measurement camera is used to capture light transmitted through thermochromic liquid crystals (TLC). These crystals change their optical properties with temperature. The experiments clearly show a unique relationship between temperature and the luminance value of the TLC. A calibration function is detected to transform the measured luminance distribution into corresponding temperatures. The developed method is applied to a model of an automotive headlamp. The data are compared with results obtained by using standard techniques such as infrared camera and thermocouple measurement. By that, a reasonable accuracy of the developed method of about +/- 0.7 degrees C can be determined. Knowing the temperature on both inner and outer surfaces, the heat transfer can be evaluated.