Luminous efficacy of daylight under different sky conditions

Daylighting is recognised as an important and useful strategy in terms of energy-efficient building design in hot climates. However, daylighting is always accompanied by unwanted solar heat gain, particularly during the cooling season. To achieve and evaluate daylighting design, solar radiation and outdoor illuminance data are needed. In 1991, a measuring station was installed at the City University of Hong Kong to measure global and diffuse solar radiation and outdoor illuminance. The measured data are analysed, and empirical models to determine luminous efficacy under different sky conditions are developed and presented. Implications for energy efficiency in building designs are discussed. Copyright © 1996 Elsevier Science Ltd.