What does the A above and S1 below on car glass mean?

[McEzra]

The meaning of A above and S1 below on car glass is: Meaning: It indicates the light transmittance of the glass. Representation: AS1 represents that the light transmittance of the glass is not less than 70%, applied to the front windshield; AS2 is below this standard, applied to door glass, rear windows, and other positions. Information about glass light transmittance is as follows: Glass light transmittance: The percentage of luminous flux passing through transparent or semi-transparent objects to its incident luminous flux. Properties: When light is incident on the glass, it exhibits three properties: reflection, absorption, and transmission. The property of light passing through the glass is called "transmission," represented by light transmittance. Light blocked by the glass and reflected at a certain angle is called "reflection," represented by reflectance. After light passes through the glass, part of the light energy is lost, which is called "absorption," represented by absorptance. Glass reflectance + absorptance + transmittance = 100%.