Photochromic lenses look like regular clear lenses when indoors but automatically darken when moving into a brighter area. They will darken in the light even on overcast days as UV rays still penetrate clouds.
Photochromic glasses are not to be confused with polarized glasses. These have a set tint that protects from glare but they aren't changeable; they don't adapt to the light in the same way photochromic lenses do.
If you want to order photochromic lenses, please follow the steps: