There are 2 different kinds of Transitions - we use Transitions signature lenses which are the best renowned and selling lenses in the UK. Transitions Signature lenses react to UV light and turn dark with becoming sunglasses. However, this does not happen while driving as your car’s windshield blocks UV light coming from the sun. If you want your Transitions to turn dark in the car then we can use Transitions Xtra active on special requests- these lenses react to ambient lighting instead of UV lights.