Evening office lighting - visual comfort vs. energy efficiency vs. performance?

During the study presented in this article, we compared two highly energy-efficient lighting scenarios for evening office lighting (i.e. electric lighting that is typically used for approxiamately 2 h in the evening). The first of these lighting scenarios (referred to as "Reference"-scenario, Lighting Power Density or LPD of 4.5 W/m(2)) has been successfully in use in many office rooms of the Solar Energy and Building Physics Laboratory's experimental building, located on the campus of the Swiss Federal Institute of Technology in Lausanne, for several years. The second lighting scenario (referred to as "Test"-scenario, Lighting Power Density of 3.9 W/m(2)) is more energy-efficient, creates higher workplane illuminances but leads to an increased risk of discomfort glare. The aim of this study was to meticulously compare the two lighting scenarios in order to find a lighting solution for evening office lighting that offers an optimal trade-off between energy-efficiency, visual comfort and visual performance.