The GB/T 40277-2021 standard specifies a method for determining the blue light diffuse reflection factor (ISO luminance) of paper, Cardboard and pulp under indoor daylight conditions. The standard is suitable for the evaluation of the surface luminance of paper, Cardboard and pulp. The test uses specific Geometry conditions and blue light filters to simulate the reflection characteristics under sunlight, ensuring that the results are internationally comparable. The implementation of the standard provides a scientific basis for the quality control of paper products, which helps to improve the conformity of the product in visual effect, printing adaptability and environment light, and provides technical support for manufacturers and users.