A phase response curve to single bright light pulses in human subjects.

Abstract in brief

• The study investigated how a brief bright light pulse affects the human circadian clock, specifically by measuring phase shifts in melatonin rhythms during controlled conditions.
• Results showed a typical type 1 phase response curve, with delays when light occurred before the body temperature minimum and advances after, and no shift at the critical phase, indicating the circadian system's sensitivity to light varies depending on timing.
• The findings improve understanding of human light sensitivity, revealing that even during the day, the circadian system can respond to light, with larger phase shifts observed when assessing melatonin onsets compared to offsets.]