A dynamic model of photosynthesis is developed, accounting for factors such as photoadaptation, photoinhibition, and the "flashing light effect." The model is shown to explain the reported photosynthesis-irradiance responses observed under various conditions (constant low light, constant intense irradiance, flashing light, diurnal variation in irradiance). As significant distinguishing features, the model assumes: (1) The stored photochemical energy is consumed in an enzyme-mediated process that obeys Michaelis-Menten kinetics; and (2) photoinhibition has a square-root dependence on irradiance. Earlier dynamic models of photosynthesis assumed a first-order dependence of photoinhibition on irradiance and different kinetics of consumption of the stored energy than used in this work. These earlier models could not explain the photosynthesis-irradiance behavior under the full range of irradiance scenarios-a shortcoming that is overcome in the model developed in this work. (C) 2003 Wiley Periodicals, Inc.