A time-dependent theoretical model based on the rate equations for all the photochemical states of bacteriorhodopsin (bR) is developed. A recursive method is adopted to solve the rate equations exactly, with an explicit temporal and intensity dependence of the population densities. Simulated results for a thin wild type bR film show that each intermediate state has a optimum population that depends uniquely on incident intensity and time. The model provides an analytical framework for optimization of bR for various electronics and photonic applications. (C) 2004 Elsevier B.V. All rights reserved.