TAPPI T 525 is an international standard method for the determination of diffuse reflection luminance (d/0) for paper, Cardboard and pulp. The standard is mainly for luminance measurement of white, near-white and natural pulp and paper. The luminance is assessed by the blue light reflection coefficient of specific Light spectra and geometric features. The test uses diffuse illumination and 0 ° observation geometry (d/0), which excludes the influence of the surface structure and orientation of the sample on the results. This method is suitable for natural pulp and paper and Cardboard made therefrom, but not for colored paper with dyed materials added that significantly absorb blue light. Luminance measurement is a commonly used indicator in the paper industry to evaluate the degree of pulp bleaching and product mass.