Crossed effects of visual factors on human thermal response

Abstract

Recently, the approach for studying human comfort indoors has been changing for a multi-domain framework once some studies have reported cross-effects between different comfort domains (i.e., thermal, visual, acoustic, and air quality). An example of cross-effects between comfort domains is the hue-heat hypothesis (HHH), referring to the possible association between lighting and the human thermal response. This paper presents a new investigation to verify the validity of the HHH. Several experiments were conducted in a test room under a fully controlled setting, combining two thermal (slightly cold and slightly hot) and three lighting conditions (blue, red, and white lights with nearly the same illuminance level). The experiments were divided into two parts, each one dedicated to a thermal setting. After acclimatisation, the participants were submitted to each colour of light for seven minutes under a constant air temperature. A total of 39 people participated twice in the experiment, each time in a different thermal condition, and before changing the colour of light, they answered a survey about their thermal sensation, thermal comfort, visual comfort, overall comfort, and perceived level of productivity. Answers were compared using statistical methods. The results did not allow to confirm the HHH, since no statistically significant differences were observed for thermal comfort and thermal sensation for the different colours of light. The only significant difference observed was for visual comfort in the slightly cold thermal condition, between red and white lights. In fact, the survey responses for visual comfort indicate that people preferred the white light. White light was also associated with better overall comfort assessment and perceived productivity in both thermal conditions, but the differences were not statistically significant. Further investigations should be performed under more thermally stressful environments and should also evaluate the physiological factors of participants as a thermal response instead of only subjective outcomes.