Figure 1

The experimental protocols. The experimental protocols are shown with an ordinate of 1 line per day and an abscissa of 24 h from midnight to midnight. Volunteers arrived in the laboratory at 09:30 on day 1. The ultra-short sleep-wake cycle, consisting of 30 min for sleep (black bars) followed by 60 min for wake (shaded bars) began at 10:30 and continued for 4.7 to 5.6 days. Three consecutive treatments (3 h bright light, yellow areas) were commenced after 38–54 h of baseline at one of 8 times. Circadian phase was assessed during the final 24 h of baseline preceding the first experimental treatment and for 24 h starting 6 h after the last treatment.