Systematic review: Acute thermal effects of artificial light in the daytime

The acute thermal effects of artificial light during the daytime have the potential to promote energy savings and enhance indoor comfort. Although the long-held hue-heat hypothesis suggests that the visual features of lighting may alter human thermal responses, there currently exists no systematic review or cross-study analysis that synthesizes and characterizes light's impact along both visual and non-visual pathways during the daytime. This review highlights evidence and physiological and psychological measures examining the presence of light's thermal effects during the daytime, as obtained from the literature. This review searched articles from PubMed, Scopus, Web of Science, and other sources and screened for articles with thorough lighting information and microclimatic conditions describing experiments conducted during the daytime and using static artificial light. Eighteen articles describing 18 studies were selected based on the inclusion criteria; these studies featured different experimental and intervention designs for the indoor environment and measurements of psychological, physiological, and behavioral responses. This research specifically reviews the experimental designs and settings in terms of lighting and microclimatic characteristics and also identifies the effective and appropriate physiological and psychological measures of light's thermal effects. Much of the literature described in this review suggests that lighting exposure during the daytime is associated with thermal-related psychological and physiological responses; the analysis results across different studies showed statistically significant associations with certain psychological (e.g., thermal sensation, preferred temperature) and physiological measures (e.g., proximal skin temperature, heart rate variability). However, some cross-study results were limited by the unavailability of key measurements and reports on lighting, microclimatic conditions, and/or thermal responses and possibly high levels of heterogeneity. In general, the findings of this review will facilitate continuing advances in this area, providing more comprehensive scientific rationales and strategies for adopting smart lighting technologies in sustainable and smart buildings.