Photochromic lenses are lenses that darken on exposure to ultraviolet (UV) radiation. Once the UV is removed (for example by walking indoors), the lenses will gradually return to their clear state. Photochromic lenses may be made of glass, polycarbonate, or another plastic.
http://en.wikipedia.org/wiki/Photochromic_lens3D glasses are not photochromic (nor they pass 80%+ light just yet,cause of all that polarizer junk)...