A model is presented for the interaction of ultraviolet (UV) light with germanium-doped silica glass. It is assumed that germanium sites work as gates for transferring the excitation energy into the silica. In the material the excitation induces forbidden transitions to two different defect states which are responsible for the observed refractive index changes. Activation energies [1.85 +/-0.15 eV and 1.91 +/-0.15 eV] and rates [(2.7 +/-1.9) x 10(13) Hz and(7.2 +/-4.5) x 10(13) Hz] are determined for thermal elimination of these states. Good agreement is found with experimental results and new UV-induced effects are predicted.