Daylight availability in Hong Kong: classification into three sky conditions

Abstract

A preliminary analysis of daylight data in Hong Kong was carried out. This analysis classified daylight data into three sky conditions—clear, intermediate and overcast—using two methods, that is, sunshine duration and cloud ratio methods. It was carried out based on data measured at the daylight station located in the University of Hong Kong main campus, which was collected during October 2006 to September 2007. The probabilities of the occurrence of the three sky conditions were 3.78% (clear), 67.10% (intermediate), 29.11% (overcast) and 4.78% (clear), 65.17% (intermediate), 30.34% (overcast) using sunshine duration and cloud ratio methods, respectively. The statistical analysis t-test showed that the two sets of probabilities were the same. It was also found that a global and diffuse horizontal illuminance of more than 10klux was available 85% of the time, which indicated that daylight illuminance was sufficiently available in the unobstructed sky of Hong Kong.