Photochromic lenses are a type of eyeglasses that darken when exposed to ultraviolet (UV) light and return to their clear state when not exposed to light: 

How they work

Photochromic lenses contain photosensitive molecules that change structure when exposed to UV light, causing the lenses to darken.

When to use

Photochromic lenses are ideal for people who need to wear glasses all the time, or for activities where you might change environments, like going from a museum to a bike ride

How they're made

Photochromic lenses are made by applying multiple layers of a special coating to the front of the lens, then depositing photochromic dyes over the coating. The dyes are then heated to penetrate the lens, and a final hard coat is applied

Types of photochromic lenses

Photochromic lenses can be made of glass or plastic. Glass lenses use silver halide crystals, while plastic lenses use spiroxazine molecules.

Factors that affect color change

The speed and darkness of the color change is affected by factors like temperature, thickness, intensity of UV light, and exposure history.

Other names

Photochromic lenses are also known as transition lenses, light adaptive lenses, or variable tint lenses.