Sky Luminance Measurements Using CCD Camera and Comparisons with Calculation Models for Predicting Indoor Illuminance

Abstract

In this study, we address the algorithm of the calculation formula from sky luminance distribution to vertical illuminance and indoor illuminance. To predict daylight, studies about sky luminance distributions and the Delight daylight model were investigated. This paper compared three well-known sky distribution models (Perez model, Igawa model, and CIE standard sky model) with measured data. The charge coupled device (CCD) camera was used as a measurement method for sky luminance distribution. Indoor illuminance values calculated with those well-known sky distribution models are compared with measured indoor illuminance data. The following conclusions were obtained: (1) In the results of R-2, mean bias error (MBE), and Cv(RMSE) analysis, the CIE standard sky model showed the lowest error rate with measured data. Between the Perez model and Igawa model, the Igawa model showed a lower error rate; (2) When we compared the sky classification of the Perez model and the Igawa model, both models classified the sky similarly to the CIE standard sky model in March. However, the classification of the sky in the CIE standard sky model, the Perez model, and the Igawa model differed in some of the July data because of high solar elevation; (3) The illuminance of the center point of the room was calculated using the well-known sky luminance distribution model, the Igawa model has a lower error rate than the Perez model in Korea.