The experience with the design and refurbishment of the artificial sky in the SAS daylight laboratory

Daylight laboratories are equipped with artificial skies for experimental research and testing daylight conditions in specific architectural models as well as for educational purposes. The latter often are meant only as attractive features to be shown to university visitors and students interested in architectural design or window applications but seldom are used for daylight research as measuring devices because these are not calibrated or are not modeling the standard ISO/CIE sky types. During the sixtieth of the last century was designed and built in the SAS Daylight laboratory an artificial sky simulating the CIE Overcast and unity (Lambertian) skies and then the recently CIE Clear Sky with the artificial sun. The representation of sky luminance patterns as well as proportional parallel sunbeam modeling was designed and calibrated in documented private protocols. After forty years since the Bratislava artificial sky was in service this laboratory equipment became almost a historical remnant with its artificial lighting by incandescent reflectors and robust theatrical dimming system. New technology progress in artificial light sources, reduction of energy demands and computer checking possibilities as well as new knowledge in daylight science in the determination of new ISO/CIE sky types form new requirements for designing or refurbishing artificial skies. In this respect older experience and new ideas are summarised in this paper.