Photochromic lenses have the ability to darken in the presence of UV light.
Photochromic lenses are clear until dangerous ultraviolet radiation (UV) is present. Once outdoors, the brighter the sun, the darker photochromic lenses become. They turn as dark as sunglasses by automatically reacting to the intensity of UV radiation.
Since photochromic lenses block 100% of the sun's eye-damaging rays and help to reduce painful, discomforting glare, they protect your eyes on cloudy days, sunny days, and everything in between. Photochromic lenses are the most convenient way for you to protect your eyes from the light you can see and the light you can’t, all while helping to improve the quality of your vision and the long-term health and well-being of your eyes.
This means healthy sight for just about everyone, anywhere, anytime!