Photochromic/Transition lenses are “light-adaptive” lenses, which, when exposed to UV light, cause photochromic molecules in dTRUE in the lenses to change their structure. This causes the lenses to tint slowly, shielding the eTRUE from UV light just like other sunglasses. These molecules change structure proportionally to the amount of UV light that passes through the lenses, so the lens will only darken as much as they need to to provide you with comfortable vision.