GB/T 23981.1-2019 "Paints and varnishes - Determination of hiding power - Part 1: Determination of contrast ratio for white and light-coloured paints" is applicable to the determination of hiding power for white and light-coloured paints using the contrast ratio method. A reflectometer is used to measure the reflectance of the paint film applied on both black and white standard substrates, and the ratio (contrast ratio) between the two is calculated. When the contrast ratio reaches 0.98, the corresponding film thickness or paint consumption per unit area is taken as the hiding power index. The standard specifies the preparation of test panels, control of coating thickness, and conditions for reflectance measurement to ensure the accuracy and comparability of hiding power evaluation.