effects of variable lighting intensities and colour temperatures on sulphatoxymelatonin and subjective mood in an experimental office workplace workplace illumination is of paramount importance in determining the employees productivity and wellbeing moreover light exerts nonvisual effects with respect to biological rhythms in this study we investigated the impact of different lighting conditions 5001800 lx 6500 k 500 lx 4000 k on sulphatoxymelatonin amt6s and subjective mood in an experimental office accommodation urinary amt6s concentrations were significantly decreased at all days of the experiment in both lights on day 3 differences between amt6s concentrations in specimen collected at 0500 pm and at 0900 am were significantly higher under variable lighting conditions analyses of a mood rating inventory revealed a benefit of variable light with respect to the dimensions of activity while deactivation and fatigue were increased in regular light on day 1 activity concentration and deactivation changed in opposite directions when comparing variable with regular illumination on two consecutive days in conclusion variable light exerts a potential advantage in indoor office accommodations with respect to subjective mood although no unequivocal differences in the profile of amt6s were found as compared to regular light