This International Standard specifies the procedure to be used for determining the 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.In addition, it specifies a method for adjustment of the UV-content to correspond to the CIE illuminant C [1] [2], 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 illumination C is taken to be representative of indoor illumination conditions because it contains a suitable proportion of UV-radiation [3] [4]. This method is not applicable to coloured papers containing fluorescent dyes. It is specific for the situation where the fluorescence occurs in the blue region of the visible spectral range.This International Standard should be read in conjunction with ISO 2469.