Direct measurement of the hemispherical transmittance and reflectance of diffuse irradiation

The optical properties of transparent insulation materials with complex structures can be characterised in many cases by the values for their transmittance and reflectance for ideal diffuse solar irradiation. A newly developed diffuse irradiation source allows quick and accurate measurements of the diffuse -hemispherical transmittance and reflectance of structured samples from 20 cm diameter up to 50 cm. Its newly developed inner coating, which consists of polytetrafluorethylene, allows the correct measurement of strongly selective angular and spectral properties of the samples.