Realization and application of a detector-based tristimulus color scale at the National Institute of Standards and Technology, USA

The recently introduced detector-based calibration method for tristimulus colorimeters has been realized. The NIST reference colorimeter has been calibrated for spectral irradiance responsivity with an uncertainty of 0.15 % (coverage factor k=2) resulting in a chromaticity uncertainty of 0.0004 (k=2) in the x and y chromaticity coordinates when a CIE Illuminant A source is measured. The color scale is realized and maintained by reference colorimeters rather than reference lamps. The color measurement uncertainty increases when sources other than Illuminant A are measured due to spectral mismatch errors of the channels. Variable reference source models have been developed so that the reference source for the colorimeter can be automatically matched to the measured test source of certain types. A model using Planckian radiation with a variable temperature has been tested and proved to be effective in eliminating the mismatch errors for incandescent lamps. Another model based on primary colors of a display has also been tested and shown to be effective.