We have developed models to describe the behavior of an optical fiber sensor which was used to detect fluorescence from a polymer resin during the cooling phase of injection molding. The optical fiber sensor was positioned at the wall of the mold cavity by using the ejector pin channel as access to the cavity. The sources of fluorescence were dyes, which were chosen because of their sensitivity to temperature and which were mixed with the resin at dopant concentrations (parts per million by weight). The behaviors of a molecular rotor dye, dimethylamino diphenyl hexatriene, doped into polyethylene, and an excimer producing dye, bis-(pyrene) propane, doped into polystyrene were the subjects of the modeling calculations. The models consist of two modules : (a) a solution to the thermal diffusion equation for the resin cooling in the mold and (b) using temperature/time profiles and, In the case of polyethylene, crystallinity/time profiles obtained from the thermal diffusion equation, fluorescence intensity as a function of time was computed. Factors incorporated in the models are : adiabatic heating and cooling, light scattering due to microcrystals of polyethylene. crystallization kinetics, temperature and pressure shift factors for viscoelastic relaxation near the glass transition temperature of polystyrene, and the thermal resistance at the resin/mold interface.