The TAPPI T 579 standard specifies a method for measuring the diffuse reflection luminance of paper, Cardboard and pulp, using a d/0 geometry (diffuse illumination/0 ° observation) and an ultraviolet D65 Light source. This method is suitable for white, near-white and natural pulp, paper and Cardboard, not chromadizing paper with significant blue light absorption (400500nm) added. Luminance is a numerical value that measures the ability of paper to reflect blue light and is a commonly used performance indicator in the paper industry. This standard realizes diffuse reflection illumination and vertical observation through an integrating sphere, reducing the influence of surface structure on luminance and ensuring the Reliability of measurement results.