According to your description, it is transition eyeglasses ( also called photochromic sunglasses). The eyeglasses are made of transition lenses (also called photochromic lenses) that enables them to activate, or darken, when exposed to the sunâ€™s ultraviolet light. And the greater the intensity of UV rays, the darker the lenses become. When the UV light gone, they lenses can fade back to clear lenses immediately. And with the change of UV light conditions, the level of tint adjusts. And the UV blockages remains at 100%.
Eyeglasses that turn into sunglasses when they are in the sun are called transition glasses or photochromic lenses. The lens material of transition eyeglasses can be made of glass, plastic, and polycarbonate. In the early time, the glass photochromic lenses have silver halides (usually silver chloride) embedded in the lenses, which cause the photochromic properties. Now the plastic photochromic lenses relay on organic photochromic molecules to react to UV rays and change the color. Both of them can turn dark when exposed to UV light and fade back to clear when they are away from UV light.
They are called transition eyeglasses. Actually, transition eyeglasses are suitable no matter for indoors or outdoors. They function very well like two glasses' s cooperating. You don' t need to worry about changing glasses when you go out from your home or go back home from outside. I even heard that wearing transition glasses is very helpful in improving your eyesight. Usually, transition glasses are very popular in teenagers who like outside activities very much, active adults and patients with special needs. If you want to get one, you can get them online, It is not that expensive.