The difficulties encountered in simulating accurately CIE Standard Illuminant D6, representing average daylight, particularly in the ultraviolet region, are considered. Accurate simulation is needed for colour measurements using colorimeters and for spectro-photometric measurements on fluorescent samples using polychromatic illumination. The ultraviolet content of a simulator can only affect the colour of a fluorescent material and the two main classes of such materials are considered in terms of how critical the ultra-violet content is. Samples were polychromatically illuminated with approximate simulations of CIE Standard Illuminants D65 and C and spectral total radiance factors measured. These results were corrected to represent the spectral total radiance factors that would be produced for ideal illuminants, by using additional quantities (true spectral reflectance and the emission and excitation spectra) determined from measurements on the samples by the NPL Spectrofluorimeter. The colour specifications of the samples were computed using the corrected spectral total radiance factors and indicate that Illuminant C was an adequate substitute for D65, for a sample representative of fluorescent signal and safety colours. An illuminant with an ultraviolet content similar to interior daylight, daylight attenuated by average window glass, was sufficient to produce an effect similar to that for D65 for a fluorescent white sample. Such a reduction in requirements for the shortest wavelengths present in a daylight simulator would allow the reproduction of the visible region to be imoroved and cheap, reliable simulators to be produced, without reducing the accuracy with which the colour specification of a fluorescent material can be measured.

Date Published: 19 February 1982
PDF: 7 pages
Proc. SPIE 0262, Light Measurement '81, (19 February 1982); doi: 10.1117/12.959720

Published in SPIE Proceedings Vol. 0262:
Light Measurement '81
Arthur W.S. Tarrant, Editor(s)