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.
