Identifying CIE standard skies using vertical sky component

This paper studies the classification of the International Commission on Illumination (CIE) Standard General Skies using vertical sky component (VSC) defined as the procedures for identifying the Standard General Skies are proposed. The performance of the recommended sky classification process was evaluated against measured data in terms of percentage error (PE) and root-mean-square error (RMSE). The results revealed that the method produced the RMSE of not more than 20% for most of classified Standard General Skies. The proposed approach provides an alternative for defining CIE Standard General Skies when the measured vertical and horizontal daylight illuminance data are available.

► We classify the CIE Standard General Skies using the vertical sky component.
► We propose a procedure for sky classification.
► The vertical illuminance for west-facing plane shows the best for sky classification in Hong Kong.
► The predicted sky-diffuse components show good agreement with the measured data.
► The proposed approach provides an alternative for defining CIE Standard General Skies.