The ASTM D1746-2015 standard specifies a standard test method for transparency of Plastic Sheets, which is mainly used for the measurement of light transmitance of Plastic films. The standard applies to all kinds of transparent or translucent plastic materials, especially those that are nominally clear and colorless. During the test, the transparency of light is assessed by the ability of the measurement ray of light to pass through the sample, and the results are expressed in regular transmittance (Tr). The standard emphasizes the influence of the design parameters of the test equipment on the results, and points out the need for caution when comparing the test results of different instruments, especially for samples with low light transmitance. This standard provides a uniform test method for the evaluation of Optical Properties of Plastic films, ensuring their reliability and conformity in practical applications.