Photochromic, or Transitions TM lenses respond to UV light. They are clear indoors and become dark, like sunglasses, when you are outdoors. They are a useful solution for people who are frustrated by carrying an extra set of sunglasses around, and for those who are particularly sensitive to bright light outside. It’s important to note that Transitions do not change instantly, they darken very quickly but the fadeback time is slower, so there can be a period of adjustment when returning indoors. They fade a little faster when combined with an anti-reflection coating.
Traditional Transitions do not usually change behind a car windscreen due to most windscreens blocking out the UV light needed to activate the lenses. However new Transitions XTRActive do partially react in the car.
All Transitions lenses provide full protection from harmful UVA/UVB rays.