A human phase-response curve to light.
Level 3 - non-randomized controlled study
Non-randomized human experimental laboratory study
PubMed 1791996 · doi:10.1016/0304-3940(91)90051-t
What was done
Using classical experimental protocols, researchers established a human phase-response curve to a single 3-h bright light pulse and evaluated the effect of light pulses administered across 3 successive cycles timed relative to the core body temperature minimum.
What was found
A light pulse centered slightly before the body temperature minimum delayed the circadian system, whereas a pulse slightly after advanced it. Maximum phase shifts were about 2 h for a single pulse and 4-7 h across 3 successive cycles. Specific light intensity, sample size, and variance metrics were not reported in the abstract.
Why it matters
The study demonstrated that human phase-shifting dynamics follow a classic phase-response curve similar to other species, dependent on the timing of light exposure relative to the circadian temperature minimum.
Limits
The abstract omits sample size, participant demographics, exact light intensity, control group details, and statistical measures of variance.
Cited by
- supports The human body's circadian clock can only adjust its timing by at most about three hours per day under optimal conditions.