What are photochromic lenses made of?

[Francis]

I just wonder what photochromic lenses are made of and cause the lenses to change color under UV rays. Can you explain it?

[Kash]

The lenses of photochromic sunglasses are lenses made of glass, plastic or polycarbonate. They will darken when exposed to glare from ultraviolet light. The lenses are also called transition lenses. They can respond to ultra-violet radiation. The tint is a patented dye that activates the lens. Variation in light conditions, temperature and lens material interact with the tint or coating embedded in the lens and cause the lens to darken and lighten. The stronger and brighter the UV light, the darker the lens will be. The process can cause the lens to fade into various stages of light and dark, depending on the amount of UV rays they are interacting with. The process is automatic and wearers of transition lenses say they hardly notice the changes as they occur.

[Malakai]

Photochromic lenses are usually made of glass, plastic and polycarbonate. If it is made of glass, in the photochromic lenses there are many molecules of substances, such as silver chloride and silver halide, which are embedded into them. These molecules will change the color when they are exposed to UV rays directly.

[Terrell]

Photochromic lenses are only made of glass in the early time. Now they are made of many materials, such as plastic, polycarbonate and high-index. There are some chemicals in the lenses that can turn dark when the UV rays hit them. So Photochromic lenses can turn dark when you are outdoors and go back to clear when you go indoors. However, photochromic lenses won't get dark enough in the car because there are less UV rays in the car.