The GB/T 2913-1982 standard applies to the determination of the whiteness of opaque white or nearly white powdery Resin and plate-like plastics. The standard specifies the preparation of test samples, instrument requirements and Measuring methods to determine the whiteness of the material, that is, the ratio of the radiant energy of its surface under the diffuse reflection of prescribed blue light to the reflection energy of the ideal total reflection diffuser. The standard also applies to fluorescent whitening plastics to ensure the accuracy of the test results. By applying this standard, reliable data support can be provided for the mass evaluation and performance control of plastic products.