Application of the Kubelka-Munk theory for the determination of the optical properties of solar absorbing paints

The possibility to predict the solar absorptance gradient by colorimetry is described. The study is performed on black spectrally selective paints used as absorber in photothermal conversion of solar energy. The Kubelka-Munk absorption and scattering coefficients of all considered paints are determined. The relation between the degree of dispersion in the paint and Kubelka-Munk coefficients in the visible spectral region is discussed. The coefficients an used further to calculate the transparency values according to principles of colorimetry. The measured solar absorptance gradient for a very thin paint layer reversibly depends upon calculated transparency for different types of paints. This result helps to express the solar effectiveness of spectrally selective paint by the transparency in the visible. (C) 1997 Elsevier Science S.A.