Photochromic lenses darken in ultraviolet light and clear indoors. Transitions is the best-known brand; most lens makers now offer their own in-mass or coated photochromic technology.
Varieties (worldwide)
Transitions photochromic lensesGrey photochromic lensesBrown photochromic lensesPhotochromic polarised lensesPhotochromic lenses for drivingIn-mass photochromic lensesCoated (spin) photochromic lensesPhotochromic sports lenses