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.
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.
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.
Transition lenses can be called Photochromic lenses too. They can darken when they are exposed to specific types of light which include UV radiation and so on. But the lenses will gradually return to their clear state if the light source is removed. Transition lenses can be made of glass, plastics or polycarbonate.
Transition lenses can work as a pair of sunglasses when you are in the sunshine. But they will return to their clear state gradually if you walk into the inside. It can prevent our eyes from the damage of UV rays. And there are advantage and disadvantage of transition lenses. The advantage is that it can be worked as a pair of sunglasses and you won't need to buy a pair of sunglasses with you anymore. The disadvantages of transition lenses is that it will take two minutes for the lenses to return to their clear state and they can't be used for driving.
The correct term for transition lenses is photochromic or photochromatic lenses. Transition lenses can have chemical reaction when they are exposed to UV rays. There are millions of molecules of substances such as silver halide or silver chloride in transition lenses. If there are no UV rays, the molecules will be transparent. But if they are exposed to UV rays, the molecules will change their shapes and lead to color changes. The more the UV rays, the more molecules will change their shapes and the more dark the lenses will be.
If you want to know how transition lenses work, you can watch it on this video. http://www.youtube.com/watch?v=FxkrySbL7YE I think the advantage of transition lenses is that they can save you money because they can work as a pair of sunglasses. If you are a current glasses user, you can buy a pair of transition glasses and experience the color changes.