Optical emission from thin Ag films excited by visible light under a non-oxygen atmosphere was analyzed as a function of time and excitation power. The emission behavior under anaerobic conditions was strikingly different from that obtained under an oxygen-containing atmosphere. Specifically, emission intensity increased as a function of time with no photoinduced signal decay. A simple mechanistic model was developed and demonstrated to accurately predict the photodynamic trends observed under both conditions. The model involves oxygen-mediated cyclic production and destruction of photoactive silver clusters on the thin film. The evidence presented here strongly supports the hypothesis that oxygen plays a key role in the "blinking" phenomenon observed on SERS-active Ag films.