Amorphous (GeS2)(x)(Sb2S3)((1-x)) films where 0.29 < x < 0.94 were prepared by thermal evaporation from previously synthetized bulk glass. The response of virgin and annealed states of films to the slightly over-band gap illumination with respect to the shift of the optical band gap (E-g(opt) ) and the slope of the optical absorption edge (B-1/2) was studied. The magnitude of photo-bleaching and photo-darkening varied with the molar fraction of GeS2 (x) (the average coordination number CN) while a maximum of photo-sensitivity was observed, with respect to the experimental error of chemical composition determination, at CN approximate to 2.6 (x approximate to 0.80). The spectral sensitivity of photo-darkening was studied for the annealed state of the most sensitive thin film.