To assess the effects of acute white and red light at an intensity of 100, 30 or 20?lx on sleep in the dark phase, we examined the sleep–wake profiles of mice exposed to 1?h/1?h L/D cycles from ZT12–22. Darkness exposure during the entire dark phase served as a control. Unexpectedly, acute red light at 100?lx induced marked NREM sleep and REM sleep oscillations, as white light did (Figure 1c). The total time spent in NREM sleep and REM sleep for the 5-h light-on period in each group was calculated. Both white and red light at an intensity of 100, 30 or 20?lx increased NREM sleep and REM sleep significantly, as compared with darkness (Figure 1d). Thus, similarly to white light, acute red light at an intensity of 20?lx or higher induced potent sleep in the dark phase.
Acute white and red light at an intensity of 100, 30, or 20?lx disrupted sleep–wake architecture and EEG power density during the dark phase.