CCT-dependent calibration for colorimeters

Currently, the most popular instrument for chromaticity measurement consists of a power detector with several color filters of transmission spectra approaching to the color matching functions from the CIE 1931 standard observers. Unavoidably, there exist mismatches between the transmission spectrum of color filters and color matching functions. Therefore, the calibration process is obviously very important to the accuracy and the precision for the chromatic tri-stimulus values measurement in the colorimeters. In spite of several methods having been developed for the calibration procedures, the correction condition is only set to one certain illumination condition. Two most adapted standard illuminating conditions are the CIE standard illuminant D65 under correlated color temperature (CCT) 6504K, and the CIE standard illuminant A under CCT 2856K. However, in the general applications, the practical illuminating conditions for measurements are very difficult to be the same as the calibration one. In this work, the impulse response analysis has been applied for the error analysis. From the spectral mismatches of the color filters in colorimeters. A quantitative formula has thus been developed for the evaluation of the correction for the chromatic tri-stimulus values due the mismatch of the color filters under various CCT illumination condition. Based on this formula, the previously unknown deviation in the chromatic measurement under different CCT condition now can be further reduced down. In summary, the filter-type colorimeters with the calibration procedure according to our correction formula will perform much higher precision but still keep its simple and convenient use.