The main applications of radiance/luminance models are reviewed here, with an emphasis on empirical modelsbased on experimental data, typically provided by sky scanners. Such measurements, and the derivedmodels, are subject to various limitations. Nevertheless, the Igawa radiance model is validated under the highelevationand low-turbidity conditions of Colorado, and found reasonably accurate under both clear andcloudy conditions. Here, the Igawa model is enhanced by combining it with a new parameterization of theclear-sky circumsolar radiance to improve the overall radiance prediction within the aureole region. Thisresults in the turbidity-dependent IGI model. Based on this new anisotropic radiance model, a real sky viewfactor (RSVF) for partially obstructed skies can be used as a basis for realistic calculations. It can be calculatedwith the SOLARES software, which is designed to accept irradiance inputs from, e.g., a typical meteorologicalyear (TMY), and thus can be used to provide hourly results at any location where a TMY or an irradiancetime series is available. A simulation is performed for an ideal solar system with or without sky obstructionand compared to the classic SVF approach, resulting in significant differences. The proposed approachcan be advantageously used in lieu of the conventional isotropic SVF method in many types of shading geometryin the built environment.
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