Phase advancing human circadian rhythms with morning bright light, afternoon melatonin, and gradually shifted sleep: can we reduce morning bright-light duration?

A 30-minute morning bright-light exposure combined with afternoon melatonin may achieve 75% of the phase shift observed with 2 hours of bright light.

• Three patterns of morning bright-light exposure were tested to determine their effect on phase advancing circadian rhythms.
• The largest phase shift of 2.4 hours was observed with the 2-hour exposure pattern.
• The 1-hour and 0.5-hour exposure patterns resulted in smaller phase shifts of 1.7 hours and 1.8 hours, respectively.
• The single 30-minute bright-light exposure was found to be as effective as 1 hour of light spread over 3.25 hours.

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