The lower correlated color temperature with higher illuminance nocturnal light environment improves cognitive performance and sleep quality

Well-designed nocturnal light environment could boost performance on the cognitive tasks and promote sleep quality after light exposure. We optimized and fabricated a four-channel mixed white light with peak wavelengths of 429, 523, 591, and 621 nm. Comparing with common white light emitting diode (LED) (5798 K, 212.7 lx), the mixed white light has lower correlated color temperature (CCT) (2799 K), higher illuminance (356.2 lx), similar melanopic illuminance, and better color fidelity. We conducted experiments on 14 healthy young subjects (7 males and 7 females; age 18–25 years) to investigate the effects of nocturnal light environments on the cognitive performances and sleep quality. In consistent with the α-opic flux model, the mixed white light with higher illuminance shrinks the pupil size and has less melanopic flux, which results in more melatonin for subjects. More melatonin before sleep benefits the sleep quality by decreasing arousal times and improving sleep continuity. The higher illuminance light environment also promotes the inhibition ability and working memory. Moreover, it presents better color discrimination and less visual fatigue. Therefore, the lower CCT with higher illuminance nocturnal light environment effectively promotes both cognitive performances in the evening and the following sleep quality.