A pilot study of the interaction between heat stress and metameric white light on occupants’ cognitive performance
Abstract
Previous studies have shown that occupants' core body temperature (CBT) increases dynamically and cognitive performance declines under high indoor temperatures. On the other hand, light illuminance and correlated color temperature (CCT) have been widely studied for their physiological and cognitive impacts within thermal comfort ranges. However, light spectral power distribution (SPD) remains underexplored. This study examined the effects of two metameric white lights - identical in illuminance and CCT but differing in spectral composition (blue-enriched vs. red-enriched) - on CBT responses and cognitive performance during heat exposure. Eight college students were exposed to each lighting condition in a climate chamber maintained at 38 °C for 1h. CBT was continuously monitored using a CardioWatch, and subjects completed cognitive tasks assessing attention, executive function, memory, and emotion. Results showed that the increase rate of CBT was smaller under blue-enriched white light than under red-enriched white light, providing initial experimental evidence that metameric white light can modulate thermo-physiological responses under heat stress. No significant differences in cognitive performance were detected between lighting conditions. However, subjects exposed to red-enriched white light performed better on the learning and episodic memory task and more frequently selected 'Happy' in the emotional bias task; medium effect sizes indicated potential practical importance. These cognitive outcomes may have been influenced by a systematic order effect. Overall, the findings highlighted the importance of light SPD as a non-visual environmental factor for modulating thermo-physiological responses and potentially cognitive performance under heat stress. Future research should adopt counterbalanced designs, larger sample sizes, various high temperatures, and more diverse populations, and validate findings in real-world workspace across seasons.