Photomechanical shape memory polymers are an exciting class of materials that are able to store a temporary shape and recover their original shape when stimulated by light. In this work we develop a model to simulate the photomechanical behavior of light-activated shape memory polymers. To the best of our knowledge this is the first theoretical model developed to describe this exciting class of active materials. Our model incorporates the interplay among four aspects of the underlying physical phenomena: light propagation, photochemistry, chemical-mechanical coupling, and mechanical response. The model framework is applied to a recently developed photo-induced shape memory polymer system [1, 2]. We describe a suite of experiments used to guide the modeling efforts, calibrate the model parameters, and then validate model predictions. Regarding the latter, we measure and then simulate the photo-induced bending behavior of shape memory polymer samples; model predictions are in good agreement with measurements. We use the model to then explore the effect of important photomechanical parameters (applied strain magnitude, irradiation time and intensity, and photoabsorber concentration) on material response with a view toward the design of novel actuator materials and structures.