What is a transition lens and how transition lenses work?

[Peak]

Because I don't know much about transition lenses, any one can tell more about transition lenses? Thx in advance.

[Pearblossom]

Transition lenses are made of photo-sensitive materials that can change from clear to dark automatically according to the amount of light in the room or outside. The lens of transition glasses is clear inside just like reading glasses, but when the transition lens is exposed to sunshine, it darkens automatically just like sunglasses. This kind of lens protects the eyes from UVR.

[Pearce]

Transition lens also called photochromic lenses. The transition lenses look like a regular prescription lenses in room but become dark lenses in sunshine. And the more intensive the sunshine, the darker the lenses.

[Pearcy]

Yes, transition lenses also called photochromic lenses, but the lenses are not dark because of sunshine but UV rays in the sunshine so that to protect eyes from UV rays. So, the stronger the UV rays, the darker the lenses.