Photochromic lenses automatically adapt to changing light conditions. When indoors photochromic lenses will be clear and when outdoors and exposed to sunlight will darken automatically. Photochromic lenses are also known as light-adaptive lenses or light intelligent lenses.

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When photochromic lenses are exposed to UV light, the molecules in the lens change and cause the lenses to darken. This can provide optimal visual comfort and protection when you need it most. Photochromic lenses can still darken even on overcast days, because UV light can penetrate the clouds making sure you’re receiving optimal UV protection. Most photochromic lenses typically won’t darken in the car as windshields block most UV light. But Essilor have produced a photochromic lens that darkens behind a windshield as well as full range of  photochromic lenses with different benefits and capacities.