A study has been made of the photo-emf of alpha-RbAg4I5 superionic crystals exposed to light from the impurity excitation region. The effects of local light irradiation and silver saturation on the photo-emf excitation spectrum were investigated. It was found that irradiation with light having energies 2.78 eV and 2.92 eV causes color centers formation in the crystals. Illumination intensity and time dependences of the photo-emf for the main excitation bands were measured at room temperature. The estimation of the photon capture cross sections for the electronic transitions gives values of the order ofmagnitude of 10(-7) cm(2). A mechanism for the origin of the photo-emf is proposed.