Sky luminance measurements and comparisons with calculation models

Measurements of sky luminance in various meteorological conditions were taken in three localities: Arcavacata di Rende (Italy), Lyon (France) and Osaka (Japan), by means of a sky scanner. The data were compared with Perez, Igawa and CIE luminance calculation models. The analysis of the comparison shows that the best luminance predictions are obtained by the CIE model, but the predictions by the CIE model need the knowledge of the measured luminance distributions themselves and, consequently, this model is, at present, only suitable for the determination of the frequency of occurrence of the CIE sky types in a given place. Between the other two calculation models, Perez and Igawa, the latter appears somewhat more accurate than the former.

► Sky luminance distributions measured in three localities are analyzed.
► The data are compared with Perez, Igawa and CIE calculation models.
► Best luminance predictions are provided by CIE model.
► If measured luminances are not available in one locality, CIE model cannot be used.
► Igawa model performs somewhat better than Perez model.