Let there be no light: The effect of bedside light on sleep quality and background electroencephalographic rhythms

Objectives: Artificial lighting has been beneficial to society, but unnecessary light exposure at night may cause various health problems. We aimed to investigate how whole-night bedside light can affect sleep quality and brain activity. Patients and methods: Ten healthy sleepers underwent two polysomnography (PSG) sessions, one with the lights off and one with the lights on. PSG variables related to sleep quality were extracted and compared between lights-off and lights-on sleep. Spectral analysis was performed to rapid eye movement (REM) sleep and non-REM (NREM) sleep epochs to reveal any light-induced differences in background brain rhythms. Results: Lights-on sleep was associated with increased stage 1 sleep (N1), decreased slow-wave sleep (SWS), and increased arousal index. Spectral analysis revealed that theta power (4-8. Hz) during REM sleep and slow oscillation (0.5-1. Hz), delta (1-4. Hz), and spindle (10-16. Hz) power during NREM sleep were decreased in lights-on sleep conditions. Conclusions: Sleeping with the light on not only causes shallow sleep and frequent arousals but also has a persistent effect on brain oscillations, especially those implicated in sleep depth and stability. Our study demonstrates additional hazardous effect of light pollution on health.