Evaluation of EN15193-1 on energy requirements for artificial lighting against Radiance-based DAYSIM

This study evaluates the calculation approach of the energy requirements for artificial lighting inside buildings of different use according to EN15193-1:2017, defining the main scope of the standard, highlighting its limitations, and proposing improvements. The evaluation was carried out through a parametric analysis to determine the influence of window-to-wall ratio, distribution of windows, presence of side opening, glazing visible transmittance, and overhang length on the calculation of the Lighting Energy Numeric Indicator (LENI) for a living room and an office at four representative locations (Bratislava, Stockholm, London, Athens). The standard was tested against DAYSIM, a Radiance-based simulation tool for calculating daylight availability, whose results were post-processed to obtain the energy requirements for artificial lighting. For many windows close to each other, the standard's approach to superimpose the daylight factors (DF) for overlapping daylit areas led to an overestimated total DF and therefore an underestimated LENI. For rooms with low window-to-facade and window-to-wall ratio, the standard's calculation was inaccurate. The daylight supply factor tabulated in the standard was too low for latitudes below 45°, leading to an overestimation of the LENI. For latitudes above 60°, the opposite effect was observed. Summarising, the standard underestimated the LENI by about 10% on average.