This International Standard specifies the procedure to be used for determining the CIE whiteness of papers and boards, in order to obtain values which correspond to the visual appearance of white papers and boards, with or without fluorescent whitening agents, when they are viewed indoors. It is based on radiance factor data obtained over the full visible spectral range (VIS) in contrast to the measurement of ISO brightness, which is limited to the blue region of VIS. This International Standard also specifies the procedures for the determination of CIE tint values and the fluorescent component of CIE whiteness. In addition, it specifies a method for adjustment of the UV content to correspond to that of CIE illuminant C [10][11], since the results obtained when fluorescent whitening agents are present are dependent upon the UV content of the radiation falling upon the sample. The CIE illuminant C is taken to be representative of indoor illumination conditions because it contains a suitable proportion of UV radiation [12][13]. This method is not applicable to coloured papers containing fluorescent dyes. It is specific to the situation where the fluorescence occurs in the blue region of the visible spectral range. This International Standard is read in conjunction with ISO 2469.NOTE 1 It is recognized that the CIE whiteness equation was developed in the context of the CIE standard illuminant D65 [6], but the similarity between the relative spectral power curves for the C and D65 illuminants within the visible region and the closeness of their correlated colour temperatures (6 770 K and 6 500 K respectively) are taken as a justification for the use of the analogous whiteness equation with the CIE illuminant C. NOTE 2 A related International Standard, ISO 11475 [4] specifies the procedure for obtaining values corresponding to the appearance of papers viewed under the CIE standard illuminant D65.