The effect of light directionality on alertness and cognitive performance during post-lunch dip

Abstract

The non-image forming effects of light are moderated by various aspects such as dose, spectrum or temporal and spatial patterns. One of them, the spatial distribution of light within the field of view, has been scarcely researched. Although few studies suggest effects on melatonin secretion during night-time, the daytime effects remain unknown. In this project, we investigated the effect of three light directions – from above, below and the side – each illuminating different retinal regions. The luminance and the size of the light source were kept constant, thus realising the same vertical illuminance and melanopic irradiance at the eye for all scenes. Forty participants underwent a two hour protocol of cognitive tasks and subjective assessments of alertness and performance. Our results suggest stronger non-image forming-effects stimulation with lighting from above, whereas the effect of lighting from below and side differed slightly.