Transmitting ultraviolet (UV) light (Ephoton > 3 eV) through optical fibers in many cases causes additional attenuation increasing with exposure time and light intensity. High- energy UV photons interact with defects in the glass structure, causing absorption bands. These mechanisms limit the applicability of quartz glass fibers in demanding applications. Currently reported measurements do not give any information about changes in the transmission of the fiber when exposed to intense UV light. To obtain these data, the transmission of optical fibers is measured during and after UV irradiation in the spectral range from 200 nm to 350 nm wavelength. These data are used to calculate the transmission changes due to photon glass interaction. To investigate the influence of UV light (deuterium lamp) on the attenuation characteristics of optical fibers, the authors produced different fiber qualities regarding UV performance. The results obtained from these measurements lead to a deeper insight into the mechanism of defect generation. UV light not only creates defects but is also able to anneal defects. Some models of this defect creation and annealing are discussed. Based on these models, UV-improved optical fibers are produced, showing less photon-induced attenuation.