Dim light at night disturbs the daily sleep-wake cycle in the rat

Links

Summary

Even very low levels of light at night (5 lux) can significantly disrupt circadian sleep architecture and SCN function, providing a biological model for how ambient nighttime lighting in homes or hospitals may contribute to insomnia. Lighting designers and healthcare facilities should treat nighttime light minimization as critical, as even dim artificial light can fragment sleep rhythms and induce internal desynchronization.

Key Findings

5 lux of dim white light at night (LDim) acutely decreased the amplitude of daily REM and NREM sleep rhythms, with further decreases over subsequent days.
LDim diminished the circadian 16–19 Hz frequency domain within NREM sleep EEG, indicating disrupted sleep quality beyond simple timing shifts.
LDim suppressed SCN clock gene expression rhythms, confirming a direct impact on the master circadian oscillator.
LDim induced internal desynchronization by introducing a free-running locomotor rhythm of ~25 h alongside the entrained 24 h rhythm, a novel finding within a standard 24 h light-dark cycle.
No effects on body weight or glucose tolerance were observed, suggesting sleep disruption preceded metabolic consequences in this model.