The calculation program under consideration determines the spectral irradiance of direct solar radiation, diffuse solar radiation and reflected radiation as well as global radiation as a factor of sun position (as determined by geographic location, season and time of day) and meteorological conditions: temperature and relative humidity, O3 concentration, degree of cloud cover and visibility as well as the spectral ground reflectance. Spectral irradiance levels are calculated for randomly positioned surfaces. The irradiance level is calculated as a function of time of day on the basis of the hourly means for the meteorological parameters as measured by many different weather stations. On this basis, the radiant exposure for a given day is calculated in terms of selectable wavelength ranges. The program also calculates the effective radiant exposure by using the spectral sensitivity of a specific material as a basis for lifetime prediction. The lifetime of a polymer material depends on several external parameters, e.g., solar radiation, temperature and moisture content of the material. The general scope of this paper is restricted to radiation and its effect on lifetime.