Conference Paper


Conference: CIE Lighting Quality and Energy Efficiency


To investigate the hypothesis that a simulation of natural daylight such as a sky with moving clouds would be desirable in offices and if this reproduction increases well-being and reduces subjective tiredness, we developed a luminous ceiling (Virtual Sky) and examined 30 test persons for three times during three weeks. In this paper we provide a technical description of Virtual Sky and the test conditions. We compared static light to two different dynamic lighting conditions. Our findings indicate that the acceptance of dynamic lighting depends on the performed tasks. Furthermore, for test candidates without access to natural daylight, subjective tiredness after one working day was significantly lower under a cloud animation compared to static light. Well-being decreased significantly less under a cloud animation compared to static light.

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    ABSTRACT: To address the absence of natural light in working spaces, virtual natural lighting solutions (VNLS) can be promising. VNLS are systems that artificially provide lighting as well as a realistic outside view with properties comparable to those of real windows and skylights. This article discusses the evaluation and analysis of various opening configurations of a second-generation VNLS prototype, which features an array of light emitting diode (LED) tiles coupled with a line of linear LED fixtures with adjustable color temperatures that provide direct light. Simulation using Radiance was performed and validated with the measurement results. Various possibilities of placing the prototypes inside the test room were investigated in Radiance to determine the effect on space availability and visual comfort. Based on the comparison of seven configurations of two prototypes with equal total opening size, it was found that nearly all configurations tested yielded a space availability of 100% with a criterion of 200 lx and where space availability is defined as the percentage of points on a horizontal grid that meet or exceed the target illuminance. Taking 300 lx as the criterion, two openings on each short wall facing each other (configuration 2) and four openings on a long wall (configuration 5) yielded space availabilities of more than 90%. Taking 500 lx as the criterion, configurations 2 and 5 yielded space availabilities between 25% and 50%. The highest uniformity (Emin/Eavg) was achieved under configuration 2 (0.59), whereas the maximum daylight glare probability (DGP) values under all configurations were between 0.25 and 0.30. Our simulation results suggest that the space availability in a private office can be optimized by placing a VNLS prototype on each short wall facing each other or by placing two on a long wall.
    LEUKOS The Journal of the Illuminating Engineering Society of North America 08/2014; 10(4):223-236. DOI:10.1080/15502724.2014.948185 · 0.96 Impact Factor