Effectiveness of evening phototherapy for insomnia is reduced by bright daytime light exposure

Sleep Med. 2011 Sep;12(8):805-7. doi: 10.1016/j.sleep.2011.02.005. Epub 2011 Aug 19.


Objective: To examine the effect of ambulatory daytime light exposure on phase delays and on the advances produced by timed exposure to bright evening or morning light.

Methods: As a subset of a larger study, 32 older (63.0 ± 6.43 years) adults with primary insomnia were randomized to an at-home, single-blind, 12-week, parallel-group study entailing daily exposure to 45 min of scheduled evening or morning bright (∼4000 lux) light. Light exposure patterns during the baseline and the last week of treatment were monitored using actigraphs with built-in illuminance detectors. Circadian phase was determined through analysis of in-laboratory collected plasma melatonin.

Results: Less daytime light exposure during the last week of treatment was significantly associated with larger phase delays in response to evening light (r's>0.78). Less daytime light exposure during the last week of treatment was also associated with a significant delay in wake time (r's>-0.75). There were no such relationships between light exposure history and phase advances in response to morning light.

Conclusions: Greater light exposure during the daytime may decrease the ability of evening light, but not morning light, exposure to engender meaningful changes of circadian phase.

Publication types

  • Randomized Controlled Trial
  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Aged
  • Aging / physiology
  • Chronotherapy / methods*
  • Chronotherapy / standards
  • Circadian Rhythm / physiology
  • Female
  • Humans
  • Lighting*
  • Male
  • Middle Aged
  • Photoperiod
  • Phototherapy / methods*
  • Phototherapy / standards
  • Sleep Initiation and Maintenance Disorders / physiopathology*
  • Sleep Initiation and Maintenance Disorders / therapy*
  • Sunlight
  • Treatment Outcome