Entrainment of a free-running human with Bright light?

Tana M. Hoban, Robert L. Sack, Alfred J. Lewy, L. Stephen Miller, Clifford M. Singer

Research output: Contribution to journalArticlepeer-review

56 Scopus citations


The case of a 40-year-old sighted woman with free-running sleep-wake and melatonin rhythms is presented. The subject was studied for 102 days. During the pre-treatment period, both the sleep-wake and melatonin rhythms had a period of 25.1 hr, similar to the average period of humans living in temporal isolation. Treatment consisted of bright artifical light exposure (2500 lx Vita-Lite) for 2 hr each day upon awakening. Clock time of light exposure was held constant for 6 days and then slowly advanced until the subject was arising at her desired time of day. The subject continued the light treatment at home and was able to live on a 24-hr day for the 30-day follow-up study. While other factors may be operating in this situation, it is possible that the light treatment caused the stabilization of the free-running rhythms, advancement to a normal phase and entrainment to the 24-hr day. We suspect that the tendency to free-run was related to sleep onsets that were abnormally delayed relative to the circadian phase response curve for light. By scheduling a 2-hr pulse of bright light each morning, this tendency to delay would be counteracted by light-induced advances, resulting in normal entrainment.

Original languageEnglish (US)
Pages (from-to)347-353
Number of pages7
JournalChronobiology International
Issue number4
StatePublished - 1989


  • Circadian rhythms
  • Melatonin
  • Phototherapy
  • Sleep

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)


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