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Abstract
Using 'classical' experimental protocols, a human phase-response curve (PRC) to a
single 3-h bright light pulse has been established. When the light pulse was centred
slightly before the time of body temperature minimum, the circadian system delayed,
whilst a pulse slightly after the minimum advanced it. Maximum phase shifts were about
2 h. When light pulses over 3 successive cycles were used, larger shifts (4-7 h) were
produced. It is concluded that the human PRC does not differ in principle from that
found in other species, except with respect to the light intensity required.