Abstract
Daylight values are frequently required in building design and yet daylight records are unavailable for most sites in Europe. This paper presents several different approaches used for the prediction of global, diffuse and direct luminous efficacies. A much simpler luminous efficacy model is also proposed. The analysis is divided into the sections which describe luminous efficacy of direct, global and diffuse irradiance. The focus of this work is the evaluation of various models against measured data from Edinburgh. In addition, a brief description of the most common atmospheric parameters incorporated in daylight models is presented. The need for these design tools is unquestionable as the models provide the relationship between a commonly measured quantity (solar radiation) and illuminance.