The Influence of Internal Coloured Surfaces on the Circadian Efficiency of Indoor Daylight

Abstract

The discovery of circadian stimulation by daylight has changed our understanding of the important effect the daylight has on our health and wellbeing. The new medical facts that emerged during the last decade have proven that a long-term absence of circadian light stimulation may be associated with sleep disturbance, tiredness and increased incidence of chronic depression, bipolar disorder, and seasonal affective disorder. The reason is the difference between the visual and biological (circadian) response to light and how it is being perceived by human beings: while the visual perception represented by the luminous efficiency function peaks at the wavelength of 555 nm, the circadian photoreception curve peaks in the blue light spectrum at ~450 nm. The primary circadian stimulation by daylight depends on the properties of light impinging on the retina. An experimental study was designed to quantify the effect of internal coloured surfaces on our circadian stimulation by daylight. Four identical models of a standard office were manufactured, equipped by wallpapers of different colours, and exposed to daylight. Illuminance and spectral distribution of light were measured at different positions along the room and the potential circadian stimulation was evaluated by an established model. The measurements have proven that although the visual comfort may be satisfactory, circadian stimulation may be inhibited, especially when room´s surfaces are yellow. Thus, proper choice of internal surfaces´ colours is important to prevent the potential negative health consequences.