Light and elevated temperature induced degradation (LeTID) kinetics in float-zone silicon are investigated by varying the initial sample state, composed of different base material, base doping, SiN x :H films, and subsequent firing, and/or annealing steps. The approach of deliberately changing the initial sample state is shown to allow for specific studies of influences of LeTID kinetics. Bulk- and surface-related degradations are examined separately and the influence on the kinetics of bulk- and surface-related degradation is illustrated by a four-state and three-state model, respectively. In case of bulk-related degradation, an increase in defect density because of the firing step is shown, whereas the annealing step has an inverse effect. Both temperature steps—individually and combined—influence the transition rates of bulk-related degradation and regeneration by presumably changing the distribution of a defect precursor. For surface-related degradation, the firing step reduces the transition rate from the initial to the degraded state. In addition, the influence of a comparably humid atmosphere and the absence of UV light are found to be negligible.