Light-induced melatonin suppression at night after exposure to different wavelength composition of morning light

Neurosci Lett. 2016 Mar 11:616:1-4. doi: 10.1016/j.neulet.2015.12.063. Epub 2016 Jan 14.


Bright nocturnal light has been shown to suppress melatonin secretion. However, bright light exposure during the day might reduce light-induced melatonin suppression at night. The human circadian system is sensitive to short wavelength light. This study evaluated the preventive effect of different wavelengths of daytime light on light-induced melatonin suppression at night. Twelve male subjects were exposed to various light conditions (dim, white, and bluish white light) between the hours of 09:00 and 10:30 (daytime light conditions). They were then exposed to light (300lx) again between 01:00 and 02:30 (night-time light exposure). Subjects provided saliva samples before (00:55) and after night-time light exposure (02:30). A two-tailed paired t-test yielded significant decrements in melatonin concentrations after night-time light exposure under daytime dim and white light conditions. No significant differences were found in melatonin concentrations between pre- and post-night-time light exposure with bluish-white light. Present findings suggest that daytime blue light exposure has an acute preventive impact on light-induced melatonin suppression in individuals with a general life rhythm (sleep/wake schedule). These findings may be useful for implementing artificial light environments for humans in, for example, hospitals and underground shopping malls to reduce health risks.

Keywords: Daytime; Light; Melatonin; Night-time; Wavelength.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Circadian Rhythm*
  • Humans
  • Light*
  • Male
  • Melatonin / metabolism*
  • Saliva / metabolism*
  • Young Adult


  • Melatonin