What is the term for lenses that darken when exposed to UV rays?

The term for lenses that darken when exposed to UV rays is "photochromic." These lenses contain special molecules that undergo a chemical change when exposed to ultraviolet light, causing them to transition from a clear state to a darker tint. This process allows them to provide protection against bright sunlight by reducing glare and enhancing visual comfort, making photochromic lenses particularly valuable for individuals who move between indoor and outdoor environments.

Polarized lenses, while they serve the purpose of reducing glare from reflective surfaces such as water or roads, do not change tint based on UV exposure. Gradient lenses feature a tint that gradually changes from dark to light, usually helpful for specific fashion aspects or for driving by allowing better vision of the dashboard but do not react to UV light. Multifocal lenses are designed to address multiple vision needs, typically for those who require different prescriptions for distance and near vision, but do not involve any tinting mechanism in response to UV light.