Parameterisation of direct illuminance for an artificial sky with sun

There are many artificial skies and simulators allowing to model daylighting under CIE overcast sky or various illuminance scenes respectively. Only some of them are equipped by an artificial sun having various constructions, like a flat panel with many small reflectors or a large parabolic reflector simulating parallel sun beams. Generally, an artificial sun in these devices is conceptually designed as a heliodon without respecting sky luminance distribution and proportion between natural sunlight and skylight. The recent trend in daylight research and practice is directed towards better evaluation of daylight availability and evaluation of daylighting in physical units. The artificial skies are appropriate devices for simulation and verification of standard daylight conditions because these guarantee stable and repeatable measurements for calibration assuming skylight and sunlight relations not only under overcast skies but also under sunny situations. To test their properties it is important to determine the parameterisation of direct illuminance, i.e. values of sunlight in lux as well as its intensity scaling for daylighting measurements in physical models. This paper presents the methodology for predetermination of sunlight illuminance levels, a discussion about the needed parameterisation and calibration with respect to the design of artificial sun within an artificial sky.