Photo-chromatic lens (Transitions)

Photochromic lenses are lenses that darken on exposure to specific types of light, most commonly ultraviolet (UV) radiation. Once the light source is removed (e.g. by walking indoors), the lenses will gradually return to their clear state. Photochromic lenses may be made of glass, polycarbonate or plastic.

Due to some limitations of glass, it is more commonly made of plastic or polycarbonate nowadays.
To date, the color options for photochromic lenses are not only grey and brown, but also grey green in order to fit different people’s needs.

Transitions is an optical company focusing on photochromic lenses. It works well with different optical laboratories and lenses manufacturing companies. It has its patented technology on this area.