Paper transparency is determined by diffuse reflection. This standard applies to white and near-white translucent paper. Ultraviolet cut-off filters are used to eliminate the effects of fluorescent whitening agents in the paper. The main principle is to calculate the transparency by measuring the luminance factor of a single-layer specimen under a black cylinder and a white backing, respectively, with a reflectance photometer. The standard describes in detail the instrumentation requirements, specimen preparation, test procedures, and calculation methods to ensure the accuracy and conformity of the measurement.