Photochromic lenses

Photochromic lenses, or transition lenses, are lenses that are translucent inside and darken when exposed to UV rays. Photochromic glasses are composed of particular molecules that darken when they come into contact with UV radiation. While they are often used as a substitute for sunglasses, photochromic glasses only activate when exposed to UV rays, meaning that in the car or in shaded areas they will not be as effective at blocking light. However, photochromic sunglasses, and even some regular photochromic glasses, are now able to darken through activation from UV and visible light.