Empirical validation of Radiance-IES daylight simulation for furnished and unfurnished rooms under a tropical sky

Nowadays, many researchers – especially engineers and architects – apply daylighting simulation tools during the building design process to investigate daylighting performance for a range of purposes. However, International Commission on Illumination (CIE, from the French name of the organisation, Commission Internationale de l’Eclairage) sky models are considered for many such simulation tools. The characteristics of tropical sky are different from those of CIE skies, hence the usage and validity of these tools could be unreliable for research involving tropical regions. The aim of this study is to validate the Radiance program in the Integrated Environmental Solution – Virtual Environment (IES-VE) software by measuring daylight in furnished and unfurnished rooms under Malaysian tropical sky. Daylighting measurement and simulation were carried out over eight days in unfurnished and furnished rooms under both intermediate and overcast skies. The case room was drawn by ModelIT and the related furniture was modelled by the Component program in IES-VE 2014. The mean difference between the measured and simulated results in the furnished and unfurnished rooms showed that the daylight factor (DF) and daylight ratio (DR) are more accurate than the work plane illuminance (WPI) and external illuminance. The study highlights furniture as a significant internal element that can effectively reduce the light levels in a room. It is concluded that the Radiance-IES relative ratios DF and DR are validated for use in furnished and unfurnished rooms under tropical skies