The S-Rating is another way of saying how dark a ski lens is. An S Rating can go from 4 to 0. They mean the following: S4: A very dark lens for a bright sunny clear day with no clouds. S3: A dark lens for a mostly sunny day with some clouds S2: A medium lens for partly cloudy days with more clouds than sun S1: A light lens for flat light conditions such as overcast, dense clouds, snow, rain or fog S0: A clear lens for night skiing or other very dark conditions