text: There are certain kinds of transition lenses nowadays that don't depend on the chemical that the lens is soaked in. They used to call this photo white photo black, for its ability to turn clear and dark under different light conditions. What happens is when light impacts the molecules that make up the lens itself, causing it to become excited at the atomic level. When this happens you have electrons jumping from a ground state to an excited state, and the resultant photon given off is of a certain energy level, which will explain why we even have a choice of colour for our transition lenses. This is largely based on the electromagnetic spectrum. When we go back into a room there is not enough light to continually maintain the higher energy quantization of the atom and it reverts back to its original ground state, a.k.a unexcited state, and it ends up clear.