Present knowledge of properties and reactions of photoexcited states of dyes and materials is discussed. It is shown that the most probable result of the absorption of daylight by the majority of colored products is the decomposition of the colorless substrate or additives or their photo-oxidation. In both reactions, radicals are produced that can change the color of dyes or colored pigments. These radicals are mostly formed by short wavelength (lambda 400 NM) light. The types of radicals that are formed by polymeric materials are described. See also AATA (6)-D2-22 and 10-956. -- AATA