Reactor light lenses

An Example of a smart material application is with reactor light lenses, also known as photochromic lenses, used in glasses. There are two types of lenses that are used, the glass version and the plastic. The glass version of these lenses uses microcrystalline silver halides, for example silver chloride in the glass. The plastic version of these lenses use organic photochromic molecules, for example oxazines and naphthopyrans. The reason both of these lenses only darken when they are used outside is because they need UV exposure from the sun. When indoors, they are like normal glasses, but when outside, they turn into sunglasses and protect your eyes by sensing the UV rays.