Daylight variations in a moderate climate as input for lighting controls

Knowledge about daylight rhythms will enable greater daylight utilisation in buildings. The goal of building design is to create spaces with maximum use of daylight, within comfort limits, while assisted by systems that respond adequately to changing daylight conditions. The development of electric lighting caused humans to move indoors and removed people more and more away from natural lighting and its triggers. Indoor lighting quality and efficiency can be improved when electric lighting and shading does not respond to human rhythms, but to naturally occurring environmental (daylight) rhythms. Possible relationships between outdoor conditions, including their frequencies, and human rhythms are of particular interest in order to have the ability to control buildings based on frequencies. In order to understand the dynamics of natural light with regards to human needs, measurements were performed. In these experiments daylight conditions were studied in a test room with two different window openings on days with diverse weather conditions. The results were linked to data collected by Actiwatches used to record spontaneous motor activity (SMA) and worn by healthy human beings. For all 24-hour data (daylight and human) Fast Fourier Transform (FFT) was used in order to transform time-dependent data into a sum of sinusoidal base functions. Results show that different lighting control strategies are necessary for different weather conditions in order to satisfy naturally occurring human rhythms.