The spring natural lighting chromaticity in interior: a case study for elderly people

Natural light, in terms of quantity, duration and time, distribution, direction and spectral power distribution, is important for non-visual processes by setting the principal biological clock to the day/night cycles and by enabling the regulation of body (heart rate, body temperature, blood pressure), mind (cognitive performances, subjective alertness, short-term memory) and behaviour (mood, appetite, wakefulness/sleep). In home environments, elderly people can suffer from the disruption of the circadian system due to the limited availability of natural light from the windows and due to the natural age modifications: the yellowing of the crystalline lenses along with the reduction of the number of neurons in the retina and in the suprachiasmatic nucleus (SCN). This paper describes the methodology of the measurements conducted through a field case study in a real domestic environment and it discusses the results of the availability and features of the natural light experienced by elderly people. This case study shows that elderly people experience insufficient levels of natural light during the morning in the spring season, with a western orientation of the windows and mainly overcast sky conditions. In these conditions, the circadian activation occurs only in the afternoon but this is inadequate for the correct regulation of the biological clock.