Sn2P2S6 is ferroelectric at room temperature. It is of technological interest in a variety of applications such as pyroelectric motion detectors and the photorefractive effect. Until now the defect structure and the light-induced charge transfer processes in this material have not been subject of a detailed investigation. The main part of this thesis describes and interprets data of electron paramagnetic resonance (EPR), optical absorption spectroscopy and their combination at 10 K to unravel the light-induced sensitization and charge transfer paths. In the photosensitized crystal at excitation with 1.5 eV a hole is transferred from a previously generated Sn3(plus) site to another inequivalent site of the ferroelectric phase. For higher excitation energies another hole present as Fe3(plus) is transferred to S2- creating S-. Optical absorption spectroscopy at room temperature indicates the validity of this model for evelated temperature below the Curie-temperature as well. It is consistent with both our interpretation of EPR spectra and the observation of photoinduced persistent conductivity that electronic bipolarons are the negative charge carriers. An additional chapter interprets a manifestation of pyroelectric luminescence already reported in other pyroelectric materials in terms of an internal Poole-Frenkel-effect induced by the pyroelectric field under changing temperature. The numerical simulation based on published material parameters is in good agreement with the experimental data for both heating and cooling.