A reader asks:
Is there an ideal number of minutes after actual sunrise for the earliest morning sun to have an optimal effect on SAD and circadian rhythm?
By “optimal effect,” we assume you mean antidepressant and circadian phase-advancing effects. 10,000 lux, the high-dose standard for white light therapy, occurs outdoors about forty minutes after sunrise. But that’s too pat an answer. Studies of dawn simulation show that antidepressant and circadian effects begin before sunrise. Dawn is a continuous event that may last 90 minutes or longer.
Based on New York data, the average SAD patient experiences remission of winter depression during the first week of April, with sunrise around 6:30 AM. There is a wide spread of dates across individuals, though. In most cases, remission occurs as early as the spring equinox around March 20-22, with sunrise around 6:55 AM, and as late as the start of May, with sunrise around 5:45 AM.
These statistics indicate that a person’s chronotype (as determined by our AutoMEQ questionnaire) influences the time of day when sunrise — and the dawn that precedes it — will have optimal effect. Evening chronotypes may respond best to light therapy at 8 AM or later, while morning chronotypes may respond best at 5:30 AM or earlier.