Light intensity and thermal responses

Temperature and light are both major factors in the design of a comfortable indoor environment. Moreover, there might be an interaction between light exposure and human thermal responses. However, results of experiments conducted so far are inconclusive and current understanding of the relation between physiological and subjective thermal effects is poor. Therefore, we tested the effect of light intensity on thermophysiology, thermal comfort and alertness. In a randomized crossover design, 19 healthy female subjects were exposed to a dim light (5 lux) and bright light (1200 lux) condition. To assess thermal responses, each light condition was offered under three temperature conditions: a cold (26 C), neutral (29 C) and warm (32 C) environment. During the experiments human energy expenditure, skin and core temperature and blood perfusion were measured under semi-nude conditions. Thermal comfort, visual comfort and self-assessed alertness were assessed using questionnaires. Preliminarily results show that both temperature and light influences self-assessed alertness (p<0.01). Additionally, a relation between thermal comfort and comfort of the perceived colour of the light condition was found (p=0.02). Knowledge on the interaction between temperature and light can be used to create healthy and comfortable indoor environments, thus allowing for extra energy savings.