The influence of LED lighting on thermal comfort, health and energy

Light is an important factor in creating a comfortable and pleasant environment. This does not solely depend on visual information, but also on non-visual effects of light like its influence on alertness, mood, sleep-wake rhythm and wellbeing (e.g. van Bommel, 2006). It is likely that light also plays a role in thermoregulation and may affect thermal comfort. Thermal comfort is a major factor regarding satisfaction with the indoor environment. However, the relation and interaction between light, thermoregulation and thermal comfort is not fully known. Light is a key factor to regulate the circadian system, thereby controlling core body- and skin temperature cycles (Cajochen et al., 2005). Bright light in the evening can increase both core body temperature and the distal to proximal skin temperature gradient (Kim and Tokura, 2007). Additionally, the hue of light seems to be able to alter thermal comfort. The environment may be perceived as warmer under reddish light and cooler under bluish light (Albers et al., 2014). Yet it is unknown whether these effects of lights are of practical significance to improve thermal comfort. Moreover, knowledge on the role of timing, duration, intensity and colour of the light exposure is missing. The main objective of this study is to investigate the relation between light, thermoregulation and thermal comfort. Furthermore, we will explore how this knowledge can contribute to comfortable and healthy buildings. Therefore, the effects of bright and dim light on thermoregulation, human energy expenditure, thermal comfort and alertness will be studied.