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1 December 1991 Optical characterization of solar-selective transmitting coatings
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There are several different kinds of coatings, both active and passive, for the control of the radiation flux through a window system. These entail coatings for the reduction of thermal heat losses in cold climates, and coatings for the reduction of not only the thermal part of the solar spectrum but also the visible part. Considerable effort is devoted to the study of optically switching films, for which the optical properties depend on certain conditions. When these coatings and films are to be used in the windows of buildings, scattering is usually unwanted, while in some applications strong scattering is a characteristic feature of the film. In either case it is important to be able to measure the scattered transmittance accurately. In this paper it is demonstrated that large errors can occur when diffuse transmittance is measured with an ordinary integrating sphere. A model is presented for the calculation of the true transmittance value from the measured signal. The separation into the diffuse and specular components is always instrument dependent. These components can vary considerably depending on the size and geometry of the sphere ports and on how the measurement is performed. By using two different modes of operation this difficulty can be reduced.
© (1991) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Arne Roos "Optical characterization of solar-selective transmitting coatings", Proc. SPIE 1536, Optical Materials Technology for Energy Efficiency and Solar Energy Conversion X, (1 December 1991);

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