On the Validity of Daylight Factor for Evaluating the Energy Performance of Building

The Daylight factor is internationally recognized as the synthetic parameter to relate indoor visual task lighting requirements and daylight availability. Nevertheless, problems related within its static nature and the absence of connection with environmental parameters and geographic location, have been repeatedly highlighted in the literature. From an energy point of view, it is used in the European standard EN 15193:2008 for evaluating daylight penetration in buildings. Standard sky for D calculation (Overcast sky) has been defined as the most conservative, and from an energy point of view, this is very useful because represents the condition of peak energy consumption for artificial lighting. The aim of this study is to verify if D calculated under other sky conditions could be more conservative from an energy point of view. Whenever this case would occur, in order to keep results on the safe side, appropriate corrections should be applied to the D in the EN 15193:2008.