The influence of light on thermal responses

Abstract

Light is essential for vision and plays an important role in non-visual responses, thus affecting alertness, mood and circadian rhythms. Furthermore, light influences physiological processes, such as thermoregulation, and therefore may be expected to play a role in thermal comfort (TC) as well. A systematic literature search was performed for human studies exploring the relation between ocular light exposure, thermophysiology and TC. Experimental results show that light in the evening can reduce melatonin secretion, delay the natural decline in core body temperature (CBT) and slow down the increase in distal skin temperature. In the morning though, bright light can result in a faster decline in melatonin levels, thus enabling a faster increase in CBT. Moreover, the colour of light can affect temperature perception of the environment. Light with colour tones towards the red end of the visual spectrum leads to a warmer perception compared to more bluish light tones. It should be noted, however, that many results of light on thermal responses are inconclusive, and a theoretical framework is largely lacking. In conclusion, light is capable of evoking thermophysiological responses and visual input can alter perception of the thermal environment. Therefore, lighting conditions should be taken into consideration during thermophysiological research and in the design of indoor climates.

Daytime melatonin and light independently affect human alertness and body temperature

“…Melatonin might therefore also affect skin temperature locally. Since melatonin affects temperature regulation on multiple levels and changes in body temperature correlate to altered alertness, it has been suggested that melatonin induces sleepiness via influencing body temperature . In our experiment, melatonin administration did not result in a significant decrease in T tongue , although subjective sleepiness increased.…”

Interactions between the perception of light and temperature

“…Two studies found a cooler thermal sensation under low light intensity as compared to bright light, while the third experiment reported no significant effect of light intensity on thermal comfort and thermal sensation . Additionally, changes in thermal sensation caused by the intensity of light may be related to changes in core body temperature . In conclusion, it remains unclear why in some studies the light exposure affected thermal sensation, while in others it did not.…”

“…This compensation may contribute to a comfortable indoor environment while simultaneously reducing building energy consumption. One theory about the interaction between temperature and light is the hue‐heat hypothesis and states that “an environment which has dominant light frequencies toward the red end of the visible spectrum feels warm and one with dominant blue frequencies feels cool.” Several studies confirm this association between light with short wavelengths and a cool thermal sensation compared to light with long wavelengths . More recently, the study of Huebner et al.…”

“…10 Additionally, changes in thermal sensation caused by the intensity of light may be related to changes in core body temperature. 5 In conclusion, it remains unclear why in some studies the light exposure affected thermal sensation, while in others it did not. The duration of the exposure and the ambient temperature may play a role.…”

“…4 Several studies confirm this association between light with short wavelengths and a cool thermal sensation compared to light with long wavelengths. 5 More recently, the study of Huebner et al…”