The Effect of Light Interventions on Nap Quality and Subjective Alertness

Abstract

The human eyes can perceive light even when napping during the day. In order to further investigate the effects of constant light exposure during napping on nap quality and subjective alertness, seven lighting conditions were designed in this paper, L0 (darkness), L1 (60 lx, 2800 k), L2 (300 lx, 2800 k), L3 (600 lx, 2800 k), L4 (60 lx, 5800 k), L5 (300 lx, 5800 k), L6 (600 lx, 5800 k). 12 participants were invited to perform a 30-minute light intervention nap experiment. Participants' Pittsburgh Sleep Quality Index (PSQI), Electroencephalographic (EEG), Karolinska Sleepiness Scale (KSS), skin temperature, and heart rate data were recorded. The results show that at L2 afternoon nap, θ band share is higher than other lighting conditions. At L6 afternoon nap, the δ band share was the lowest. High illuminance and low CCT significantly affected immediate subjective alertness during nap wakefulness, but reduced afternoon alertness was not related to light during nap. Although post-nap vigilance was lowest in L0 darkness, it rose rapidly to a maximum within 30 min of waking. From 0-25 min of napping, heart rate decreased significantly at L1  vs. L4, and skin temperature increased significantly at L2 vs. L5. None of the seven lighting conditions (L0-L6) inhibited participants' napping to a greater extent, and high illuminance and high colour temperature did not significantly increase the level of nap arousal (25-30 min).