Photochromic glasses and goggles are eyewear that can automatically adjust their tint or darkness in response to changing light conditions. These lenses contain special photochromic molecules that react to ultraviolet (UV) light, causing the lenses to darken when exposed to sunlight and return to their clear state when indoors or in low light conditions. 

Photochromic lenses are designed to be sensitive to UV radiation. When exposed to UV light from the sun, the lenses will darken to reduce glare and protect the eyes from harmful UV rays. When the UV light diminishes, such as when you go indoors or when the sun goes down, the lenses gradually return to their clear state.

Photochromic glasses and goggles are versatile and can be used for a wide range of activities. They are popular for outdoor sports and activities such as motorcycling, cycling, skiing, hiking and many more as they provide clear vision in both bright and low-light conditions.