The Influence of the Illuminant on the Luminescent Radiance Factor Spectrum of a Reference Fluorescent Paper

Present ISO standards for the measurement of the Brightness, Whiteness, and Colour of fluorescent papers require adjusting the ratio of UV light to visible light in the illumination to match CIE Illuminant D65 or C. This procedure is shown to be faulty because a true D65 colorimetry of paper requires matching the spectral intensity distribution of the illuminant and not just the net UV content. The detailed shape of the emission spectrum depends on how much the UV spectrum of the illuminant weights the corresponding features of the excitation spectrum. The shape of the excitation spectrum varies among fluorescent white papers. In light of the composite nature of the excitation spectra of fluorescent papers, the only way to perform colorimetry reliably with respect to a standard illuminant is to use a light source with a spectral distribution that matches the spectral distribution of the standard illuminant.