AbstractAn international intercomparison of the results of chromaticity and photometric measurements on retroreflecting materials was made to assess the accuracy of such measurements with current laboratory techniques. A representative group of 44 samples in six colours, including both enclosed and encapsulated constructions, was circulated to ten laboratories in Europe and the USA for measurement under closely defined conditions simulating nighttime use. A selection of 15 of the samples was also measured under simulated daytime conditions. This paper describes the daytime measurements and complements and earlier paper which gave the nighttime results. The measured chromaticities show a large overall spread covering an appreciable fraction of the chromaticity regions likely to be permitted in specifications. Spectrophotometric methods gave results in closer agreement than tristimulus measurements. Research into improved measuring techniques is needed to reduce the spread between laboratories to an acceptable level.