Exploring the impact of daylight quality on human responses under warm temperature: a living lab study

Light quality plays a crucial role in shaping our well-being and work performance. In this study, we aimed to explore whether daylight quality affected people's perception of thermal and visual comfort, concentration, and well-being. Our controlled experiments took place in a living lab, simulating a typical office environment. A diverse group of 24 healthy adults (12 females) with at least one year of adaptation to Danish weather participated in six experimental sessions during the fall season. Participants experienced one hour of exposure to 29°C. Three types of window glazing were tested: low iron, low emissivity, and tinted. Participants were exposed to two different urban views: a courtyard and a parking lot. Participants provided subjective assessments of the indoor environment and self-reported performance, concentration, and stress four times during each session. Concentration and task engagement were measured twice per session. Skin temperature at seven body parts and heart rate variability were continuously monitored. Thermal and lighting parameters were recorded every minute. When exposed to tinted glazing, participants exhibited lower concentration performance, reduced thoroughness, and decreased task engagement. Thermal comfort was poor for most participants, whereas thermal acceptability was higher with low-e and tinted glazing. More participants were comfortable with the daylight levels at the desk when exposed to low-e and low iron glazing compared to tinted glazing. Our findings underscore the importance of considering daylight quality in indoor environments. Architects, designers, and facility managers should consider the impact of glazing choices on occupants' cognitive functioning and well-being. Further research is warranted to explore these effects across larger populations and diverse contexts.