Each Photochromic lens contains millions of organic molecules that change shape and absorb light when exposed to ultraviolet radiation (UV). The degree to which they change depends on the intensity of the UV. Seeing as the amount of UV is often relative to the brightness of visible light, the lenses darken and lighten as needed. Though the changes primarily depend on UV, the lens always provides 100% UVA, UVB and UVC protection, no matter how bright it is outside or how dark the lens is at any given time.
Though the duration of a complete transition is dependent on many factors including air temperature and UV intensity, the shift starts instantly when exposed to sunlight and is continuously in a state of flux. But speed is not the only measure of a high quality Photochromic lens. Most other Photochromic lenses are simply dipped in the photosensitive material. Ours are injected, meaning the active layer is embedded within lens material. The result is a longer-lasting, high-clarity lens that is less susceptible to damage.