New Method for Measuring Colorimetric Properties of FWA-Treated Paper

A new method is proposed for measuring the total spectral radiance factor B(λ), from which all colorimetric values are derived, of paper treated by FWA (fluorescent whitening agent) illuminated by a specific standard illuminant. The method replaces unstable real fluorescent standards by bi-spectral luminescent radiance factor data that works as virtual fluorescent standards. This method was used to measure total spectral radiance factors by two illuminants for fluorescent standard paper supplied by STFI, and the ISO brightness and CIE whiteness were derived from them. The values agreed with values assigned by STFI well enough to prove the validity of the method. Total spectral radiance factors of four FWA-treated papers with fluorescence eliminated or suppressed were also measured by the method and those colorimetric values were derived from them.