The present invention relates to a process for bleaching or dyeing keratin fibers, in particular human keratin fibers such as the hair, comprising a step of application, to said fibers, of a composition (A) containing one or more chemical oxidizing agents and a step of irradiation of said fibers by means of UV-visible radiation having a wavelength ranging from 200 to 800 nm and a fluence ranging from 1 to 5000 J/cm2, after application of said composition (A); when the process is a process for dyeing keratin fibers, then one or more oxidation dyes is or are also used.