The impact of morning light intensity and environmental temperature on body temperatures and alertness

Abstract

Indoor temperature and light exposure are known to affect body temperature, productivity and alertness of building occupants. However, not much is known about the interaction between light and temperature exposure and the relationship between morning light induced alertness and its effect on body temperature. Light intensity and room temperature during morning office hours were investigated under strictly controlled conditions. In a randomized crossover study, two white light conditions (4000K, either bright 1200lx or dim 5lx) under three different room temperatures (26, 29 and 32°C) were investigated. A lower room temperature increased the core body temperature (CBT) and lowered skin temperature and the distal-proximal temperature gradient (DPG). Moreover, a lower room temperature reduced the subjective sleepiness and reaction time on an auditory psychomotor vigilance task (PVT), irrespective of the light condition. Interestingly, the morning bright light exposure did affect thermophysiological parameters, i.e. it decreased plasma cortisol, CBT and proximal skin temperature and increased the DPG, irrespective of the room temperature. During the bright light session, subjective sleepiness decreased irrespective of the room temperature. However, the change in sleepiness due to the light exposure was not related to these physiological changes.

Interactions between the perception of light and temperature

“…The current manuscript focuses on the interactions between the perception of light exposure and the perception of ambient temperature. Results of these studies on the alerting effects of light in relation to thermophysiological parameters (body temperatures) are reported elsewhere . The study design of both experiments was similar, consisting of two sessions with three time blocks with different ambient temperatures.…”

“…Skin temperatures were measured by iButton dataloggers (DS1922L, Maxim) . These were attached to 26 body sites as reported in a previous study . Mean skin temperature (Tmeanskin) was calculated using skin temperatures measured at the 14 ISO‐defined skin sites .…”

“…Results of these studies on the alerting effects of light in relation to thermophysiological parameters (body temperatures) are reported elsewhere. 17,18 The study design of both experiments was similar, consisting of two sessions with three…”

Daytime melatonin and light independently affect human alertness and body temperature

“…Light‐induced melatonin suppression is associated with decreased sleepiness, although probably not at intermediate indoor light levels . Melatonin ingestion increases subjective sleepiness and lowers CBT, but CBT manipulations affect subjective sleepiness at times of day when melatonin is virtually absent, suggesting a relationship between CBT and sleepiness independent of melatonin …”

“…10,11 Melatonin ingestion increases subjective sleepiness and lowers CBT, 12 but CBT manipulations affect subjective sleepiness at times of day when melatonin is virtually absent, suggesting a relationship between CBT and sleepiness independent of melatonin. 13 Alertness is known to affect many functions, such as performance, psychological and physiological well-being, caloric intake, and pain sensitivity. [14][15][16][17] Displaying optimal alertness is thus beneficial, and many studies have attempted to improve alertness using monochromatic or polychromatic light (for review see, 18,19 ).…”