Driving Photochromic Polarized SunglassesWhat are photochromic glasses? Photochromic lenses have millions of molecules of substances such as silver chloride or silver halide embedded in them. When exposed to UV rays, as in direct sunlight, the molecules undergo a chemical process that causes them to change shape. The new molecular structure absorbs portions of the visible light, causing the lenses to darken, and to improve vision while ensuring protection from hazardous optical radiation.