The dim light melatonin onset as a marker for orcadian phase position

Alfred J. Lewy, Robert L. Sack

Research output: Contribution to journalArticlepeer-review

351 Scopus citations


Masking is known to affect a variety of circadian rhythms, making it difficult to use them as reliable markers of circadian phase position. Melatonin may be unique in that it appears to be masked only by (bright) light. Sleep and activity do not appear to influence the melatonin rhythm. By measuring the onset of melatonin production, a clearly demarcated event, we can reliably assess circadian phase position, provided blood is sampled under dim light (the dim light melatonin onset, or DL.MO). The DLMO has been useful in assessing the phase-shifting properties of bright light and in phase typing patients with chronobiologic disorders, such as winter depression.

Original languageEnglish (US)
Pages (from-to)93-102
Number of pages10
JournalChronobiology International
Issue number1
StatePublished - 1989


  • Bright light
  • Circadian rhythms
  • Masking
  • Melatonin
  • Winter depression

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)


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