Polarization is the process of restricting vibrations of light wholly or partially to one direction. This controls how the light will be reflected and therefore assists in clearer vision. Sunglass lenses that are polarized reduce glare from surfaces where a reflection may be present such as the window of the car driving in front of you, or a swimming pool.
A clear lens cannot be polarized, but a slight grey tint can be added to protective lenses for added protection from the sun.
Anti-Reflective lenses have an optical treatment applied to the lens. This treatment can improve the contrast of images by eliminating stray light. It also makes the glasses more cosmetically appealing and produces minimal glare.
Photochromic lenses are lenses that darken when exposed to UV radiation. Traditionally these lenses are known as “transition” lenses. These lenses darken substantially within one minute of UV exposure and will continue to darken slightly over the next few minutes. Once you are out of UV light radiation, the lenses will begin to clear immediately and are noticeably clearer in just a couple of minutes. The general time frame for photochromic lenses from darkest to clearest is between five to 15 minutes. Lenses of this type can be made from either glass or plastic.