The propagation of sinusoidal pulses in bacteriorhodopsin films has been theoretically analyzed using a complete study of the photoinduced processes that take into account all the physical parameters, the coupling of rate equations with the energy transfer equation and the temperature change during the experiment. The theoretical approach was compared to experimental data and a good concordance was observed. This theoretical treatment, can be widely applied, i.e when arbitrary pump and/or signal is used or in the case of the pump and signal beams have different wavelengths. Due to we have performed a rigorous analysis, from this treatment the corresponding two level approximation has also been analyzed for these systems.