Acute Neurocognitive Effects of Spectrally Tuned Electric Lighting in Mild Cognitive Impairment: Illuminance and Correlated Color Temperature Impacts on Vigilance and Radiovisual Performance

This study examined the acute effects of electric lighting parameters (illuminance and correlated color temperature (CCT)) on vigilance and subjective alertness in older adults with mild cognitive impairment (MCI), with direct relevance to architectural lighting design in senior-care and rehabilitation settings. A within-subject experimental design was used with nine older adults diagnosed with MCI. Participants completed the NASA Psychomotor Vigilance Task (PVT) under four lighting conditions: 350 lux at 2700 K, 350 lux at 6500 K, 478 lux at 2700 K, and 478 lux at 6500 K. To account for repeated testing, practice-related changes across sessions were explicitly considered in the interpretation of outcomes. Subjective measures included the Karolinska Sleepiness Scale (KSS), the Groningen Sleep Quality Questionnaire, and two lighting evaluation surveys. Data analyses included paired-sample t-tests, effect sizes (Hedges’ g, η2), odds ratios, and confidence intervals. Across sessions, PVT performance improved overall, consistent with a practice effect. On Day 1 (350 lux), minimum reaction time did not differ between 2700 K and 6500 K; however, maximum reaction time was shorter under 6500 K, suggesting a selective reduction in extreme slow responses under cooler-spectrum light at baseline. On Day 2 (478 lux), minimum reaction time improved significantly under 6500 K, indicating faster responses under cooler-spectrum light when combined with higher illuminance and repeated exposure. False starts and lapses did not show consistent condition-dependent differences. Overall, cooler-spectrum light did not uniformly shift mean performance but instead appeared to stabilize performance by reducing extreme slow responses at baseline and enhancing rapid responses under higher illuminance with repeated exposure. These findings suggest that practice effects and spectral sensitivity jointly shape vigilance outcomes in older adults with MCI. From a building design perspective, the results support the potential value of tunable lighting (adjustable CCT and illuminance) as a non-pharmacological strategy to help sustain daytime alertness in senior-care and rehabilitation environments.