Light and Perception: Study of the Effects of Daylight and Artificial Light on Affect, Mood, and Sleepiness Under a Sky-Lighting Machine

We investigated whether light conditions have an impact on self-reported mental states, perception, and perceived health symptoms in an exploratory study. Twenty-eight participants, divided into groups of two, experienced the same room in two diffused-light conditions (daylight [DL] or static artificial Light [AL]), which were experienced in a repeated measure design layout, controlled for order. Both light conditions offered a stimulus of at least 250 melanopic equivalent daylight illuminance (mEDI) lx, without a view. Participants were observed during two tasks—an individual reading session and a collaborative construction game session. The results show an effect of light condition on mood and pleasure, mood was higher and pleasure was better in the daylight condition. We did not find an effect of light condition on arousal and on sleepiness during the whole duration of the sessions, although results indicate lower sleepiness in DL during the construction game session. Results indicate that the recommended mEDI levels can be maintained in a day-lit-only space during working hours (9:00 to 17:00 h) around the equinox in Stockholm, 59° N. The current results show that the effects on self-reported mood and pleasure do significantly differ between light conditions, although participants were not aware whether the source was artificial or natural. Thus we presume these effects could be even more relevant in a room with a view. We also suggest that the experience we gathered through this exploration could be of inspiration for lighting design that integrates daylight and artificial lighting dynamics.