Both the experimental and mathematical analysis procedures used by the coatings and polymeric building materials communities for characterizing the photodegradation effects of UV radiation are different from those used by the medical, biological, and agricultural communities. In the building materials community, total ultraviolet radiation is monitored for characterizing the degradation effects of UV radiation. In these other disciplines, however, field and laboratory photodegradation data are related through total effective dosage, which is derived from the cumulative spectral UV irradiance to which a material is exposed along with the material's spectral absorption and guantum yield coefficients. Total effective dosage has been shown to be a good predictor of human response to solar UV radiation. The mathematical basis for determining the total effective dosage, the underlying assumptions, and supporting data and models are presented.