In high temperature solar energy applications highly concentration optical systems, such as, e.g., parabolic dishes, achieve typical tradition flux densities {gt}2 MW/M{sup 2}. In order to investigate thermo and photochemical reactions at temperatures {gt}1500 K and radiation flux densities {gt}2 MW/m{sup 2} a solar furnace was built at Paul Scherrer Institute (PSI). This furnace is a two-stage concentrator. The first stage is a prefocusing glass heliostat with a focal length of 100 m. The second stage is an highly concentrating parabolic dish with a focal length of 1.93 m. To design experiments to be carried out in the focal region of the parabolic dish, the radiation flux as well as its density distribution have to be known. This distribution is usually measured by radiometric methods. However, these methods are generally rather troublesome because of the high temperatures involved. In this paper the authors present a simple method to estimate the characteristic features of the radiation flux density distribution in the focal region of the concentrator system.