Beyond hue and heat: A multi-site experimental study of lighting–thermal interactions in human perceptions

This multi-site experimental study investigated the Hue-Heat Hypothesis (HHH), which posits that light hues can influence human thermal perception, as well as broader cross-modal interactions between visual and thermal domains. Across 464 experimental sessions in eight test rooms around the world, participants were exposed to varied thermal conditions (∼20 °C, ∼24 °C, ∼26 °C, and ∼28 °C) and typical white-light Correlated Color Temperatures (CCT, warm light: ∼3000 K; neutral: ∼4000 K; cool light: ∼6000 K) from LED sources (horizontal illuminance: ∼500 lx). The study assessed thermal, visual, and overall perceptions. Results revealed that thermal sensation and preference were predominantly influenced by thermal conditions, gender, and the laboratory setting, indicating that no statistically significant effects were found in support of the HHH. Similarly, visual perceptions were influenced by lighting conditions but not by the thermal environment. For instance, cool light was perceived as brighter than warm light, leading participants to prefer brighter light under warm light hues. Ultimately, this research revealed the significant challenges of interlaboratory experiments in this field, as local climate and test-room characteristics complicate both the conduct and the standardization of data analysis. Our findings highlight both the limited role of white-light CCT in shaping thermal sensations and the methodological challenges of multi-site comfort research, underscoring the need for careful data harmonization and context-aware analyses in future international collaborations.