Personal control of correlated color temperature of light: Effects on thermal comfort, visual comfort, and cognitive performance

Recent studies have suggested that thermal and visual comfort are correlated, although the causality underlying this correlation is unclear. Personal control of correlated color temperature (CCT) provides individual visual comfort, but its effects on other parameters such as thermal comfort and cognitive performance remain underexamined. Therefore, we investigated if personal control of CCT can, on top of visual comfort, enhance thermal comfort and cognitive performance in office scenarios while exposed to mild cold (17 degrees C) using a 2x2 within-subject design. Sixteen participants were initially exposed to CCT of either 2700 K or 5700 K for 70 min. In the subsequent 70 min, participants either had free control of CCT or no control. As expected, personal control of CCT improved visual comfort and mitigated perceived eye-related symptoms. However, it did not significantly affect thermal comfort for either antecedent CCT. When the antecedent CCT was 5700 K, personal control of CCT increased alertness and physiological arousal, improved the planning and verbal cognitive performance, but, unexpectedly, decreased performance on mental spatial manipulation tasks. Additional analyses then explored the role of the psychological and personalization effects of personal control by controlling for the actual CCT. These suggest that control benefited visual comfort, eye-related symptoms, perceived task performance, pleasure, alertness and physiological arousal. This study is one of the first studies to demonstrate that visual comfort does not causally affect thermal comfort. Personal control of CCT benefits visual appraisals and eye-related symptoms, sometimes improves alertness, but differentially influences cognitive performance depending on the task type.