Photochromic lenses are one of your options when selecting eyeglasses. They’re the type of lens that transitions to a darker color when exposed to the sun or other sources of UV light.  Photochromic lenses are ideal for people who need to wear glasses all of the time. The two main purposes of photochromic lenses are to protect your eyes from UV light and to eliminate the need for a separate pair of prescription sunglasses.