We present a microscopic model that adequately describes experimental experiences of photodarkening (PD) investigations and is based on appropriate micro-optical mechanisms. The PD effect is treated as a relaxation process of a statistical ensemble of micro-optic centers (PD complexes) that are reversibly converted into color centers by the energy of pump photons, causing the measurable PD loss. The measurement parameters prove to be fundamental for the dynamics and statistics of the PD complexes and thus have a deeper physical or statistical significance. Our model is based on measurements on pristine fiber samples. Its performance is supported by its applicability to relaxation processes in non-pristine samples.