The influence of the incidence angle on the transmittance of natural light through transparent materials

Abstract

Based on spectrophotometric measurements, glasses and others transparent materials were clustered according to their curves of visible light transmittance (Tv) variation as a function of the incidence angle. For each group, a hypothetical reference material was defined, for which a generic Tv equation was obtained, with specific parameters for each group, making possible to calculate for that material the value of Tv for all light incidence angles. Values for others materials of the group are calculated through the multiplication of the reference curve values by an adjustment coefficient that in the presented method is the value of transmittance for normal incidence of the considered material. The definition of reference curves for transmittance variation with the incidence angle minimizes the necessity of tests for optic characterization of transparent materials. It allows obtaining values of visible light transmittance for any incidence angle of a large variety of thicknesses and compositions of transparent materials, based on the material group and on its transmittance value for the normal incidence. Data obtained through this method can be used for calculation procedures of natural light availability, in which the real angle of light incidence on transparent material is taken into account.