The current study aims to investigate the effects of dynamic lighting on humans’ wellbeing, sleep quality and physiology in an office setting compared to standard static lighting. The variation of the dynamic lighting is based on humans’ circadian rhythms, in this case we chose the wake-rest cycle (Zulley, 1995). Previous research has shown that high illumination levels as well as high colour temperatures increase subject’s alertness and activity. Also higher concentration and motivation levels could be found when lighting with high illumination levels and high colour temperatures were applied (van Bommel, 2006). Vigilance and alertness of people should though not be increased while ignoring the time of day and the natural rhythm, since this could create several disorders (Boyce, 2006). A review by Begemann et al. (1997) on dynamic lighting claims that people prefer to follow a daylight cycle instead of constant levels and that individual lighting levels correspond to individual circadian rhythms. He concludes that meeting biological lighting goes far beyond solely meeting visual needs.This quas-iexperimental cross-over study employs one independent variable which is split into an endogenous condition (the illumination level supports the wake/rest cycle by becoming lower during rest periods and getting higher during wake periods) and an inverse condition which contradicts the circadian wake/rest cycle. Both conditions will be compared to a 2-week baseline/standard static condition. Thirty-five persons of 3 different open plan offices are included in the study. To control for seasonal effects, two offices (20 persons in total) will start with the endogenous condition and one office (15 persons) will start with the inverse condition. Both lighting conditions will last for three weeks with a 2-week washout period in between. Each week (will always be the same day of week) during baseline, the two test conditions and the washout period, following variables will be collected to determine the effects on wellbeing, sleep quality and physiology.Wellbeing:Multidimensional Mood Questionnaire (Steyer et al. 1997)Medical condition List (Zerssen, 1976)Recovery-Stress QuestionnaireSleep Quality:The Pittsburgh Sleep Quality Index (Buyesse et al.,1989) Physiology:24hours-hear rate and heart rate variability recordings Saliva cortisol measurements Melatonin measurementsAdditionally, semantic differentials and satisfaction with the office environment are determined. As control variables weather conditions, electric smog and acoustics are assessed.For statistical calculations a two-factorial ANOVA for repeated measurements will be performed.We expect that the endogenous lighting conditions will increase wellbeing, sleep quality and benefit physiology in contrast to the inverse condition. Data collection has just started and will last till the end of February.