Massive photoinduced short- and medium-range structural changes (photopolymerization) in As-S glasses are induced by near-bandgap light and studied by Raman scattering. Structural changes involve bond restructuring in sulfur-rich nanodomains of these nanoscale-phase-separated glasses. The spectral dependence of the photopolymerization effect demonstrates that various wavelengths can be used to optically change the structure of As-S glasses. The immense structural changes are relevant to recent findings about the role of bandgap light illumination for fabricating channel waveguides in noncrystalline arsenic sulfides.