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S. Dervishi, A. Mahdavi:
"A simple Method for the Derivation of Illuminance Values from Radiance Data";
Talk: BauSim2010 - Building Performance Simulation in a Changing Environment, Technische Universität Wien; 2010-09-22 - 2010-09-24; in: "BauSim 2010 - Building Performance Simulation in a Changing Environment", A. Mahdavi, B. Martens (ed.); Verlag / Organisation / Universität mit wissenschaftlichem Lektorat, Wien (2010), ISBN: 978-3-85437-317-9; 495 - 498.

Daylight simulation applications require information on sky luminance distribution. Sky distribution maps can be generated synthetically, but the process requires external illuminance information for calibration purposes. As measured external illuminance levels are not available for many locations, the more widely available irradiance
measurements can be translated, using proper luminance efficacy functions, into illuminance values. In this context, the present paper compares five alternative luminous efficacy models for the
prediction of external illuminance based on irradiance. The first option is based on a fixed global luminous efficacy assumptions. The other options consider potential dependencies of luminous efficacy
on outdoor temperature and humidity ratio. The models are first derived based on a first set of measured data and then test against a second set of empirical observations.

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luminous efficacy, irradiance, illuminance, temperature, humidity ratio