PhotoFusion lenses rely on a patented photochromic technology that reacts to the ultraviolet radiation in sunlight. This adjusts the tint of the lens automatically based upon ambient light levels. Exposure to excessive light initiates a photochemical reaction that alters the configuration of the photochromic molecules in PhotoFusion lenses. In this new configuration, the molecules absorb visible light, causing the lens to darken. Once the lenses are removed from sunlight, the photochromic molecules return to their original configuration, causing the lens to fade back to clear.