This standard is one of the methods in the color fastness testing series. It specifies the instrumental quantitative determination of whether the color of various textiles reaches a specific "1/1 standard depth." This method serves as an objective supplement to traditional visual assessments, aiming to ensure that the evaluation of various fastness properties of dyes and colored textiles is conducted under a uniform and comparable benchmark color depth. The standard defines specific operational procedures, including measuring and calculating the lightness value (L*) of the sample in the CIELAB color space, and determining compliance by comparing it with the target value using a formula. The required testing instruments for the experiment are photometers or colorimeters that meet the specified requirements. Measurements must be performed using the D65 standard illuminant and a 10° field of view optical geometry.