Light-induced effects in a-GexSe100-x chalcogenide glasses, i.e., photobleaching (PB), photodarkening (PD), and photoinduced structural transformations, have been investigated as a function of composition across the glass-forming region by an optical two-laser-beam technique, Raman analysis, and first-principles simulations. It was found that there is a critical concentration of Ge x≈30% that corresponds to the crossover from transient PB to the mixture of transient PD and metastable PB. At the microscopic level, this corresponds to the change in the photoexcitation process. At low-Ge concentration (x≈ 30%. Further, an increase in Ge concentration (x>30%) favors breakage of the Ge-Ge bonds upon photoexcitation and formation of light-induced 3D nanostructures. The bond conversion process is verified by Raman analysis.