High‐accuracy Colorimetry— A Review of Some Recent Work

The sources of error in colorimetry and spectrophotometry are first reviewed, and particular attention is paid to the discrepancies introduced between measurements made on different instruments arising from the variety of illuminating and viewing conditions that are employed. Reference is made to the degree of polarisation present in the light emerging from a prism monochromator and to the error this may cause in the measurement of the spectral luminance factor if the sample is illuminated at 45 and viewed normally. If these directions are interchanged, the error is eliminated. A project on high‐accuracy colorimetry in progress at Imperial College is then described in which the spectral reflection curves of a set of grey tiles ranging from black to white have been measured. Inter‐comparison between some 30 laboratories is also in progress. The application of these tiles to the accurate colour measurement of other samples by differential spectrophotometry is envisaged. Experience on the agreement between colour measurements made with several different instruments is reported and the requirements of a set of samples to be used as working standards for photometry and colorimetry are discussed.