Combined effects of thermal stress and correlated color temperature on perceived workload and subjective fatigue

This experimental study investigated the combined effects of thermal stress and correlated color temperature (CCT) on perceived mental workload, subjective fatigue, and working memory performance. Thirty healthy male participants were exposed to nine environmental combinations in a controlled climatic chamber, comprising three thermal conditions thermoneutral ( T a = 22.0 ∘ C , WBGT = 16.5 ∘ C ), moderate heat ( T a = 28.5 ∘ C , WBGT = 22.8 ∘ C ), and high heat ( T a = 35.0 ∘ C , WBGT = 29.2 ∘ C ) and three CCT levels ( 3000 K , 4500 K , and 6500 K at 500 lx ) during a 2-back cognitive task. Repeated-measures ANOVA demonstrated that heat stress significantly elevated NASA-TLX workload scores, increased MFI-20 subjective fatigue, and degraded task accuracy (all p < 0.001 ). Furthermore, significant interactive effects between thermal stress and CCT were identified across all parameters ( p ≤ 0.001 ), with the combination of high heat stress and cool lighting ( 6500 K ) producing the most pronounced adverse strain. Repeated-measures correlations confirmed strong negative associations between working memory accuracy and both fatigue ( r rm = − 0.68 ) and workload ( r rm = − 0.62 ). These findings demonstrate that simultaneous thermal and lighting stressors non-linearly impair cognitive performance, supporting the implementation of warm-to-neutral CCTs ( 3000 – 4500 K ) in thermally challenging indoor workplaces.