Before revision: When light is shining, an electron will occasionally move right by absorbing a photon and going from A to B to C. However, it will almost never move in the reverse direction, C to B to A, because the transition from C to B cannot be excited by photons, but instead requires an improbably large thermal fluctuation.
After revision: in response to the time-varying electric field of lightWhen light is shining, an electron will occasionally move right by absorbing a photon and going from A to B to C. However, it will almost never move in the reverse direction, C to B to A, because the transition from C to B cannot be excited by photons, but instead requires an improbably large thermal fluctuation.