Sleep Timing Disorders and LIGHT


Obeying the Laws of Photobiology

by Madelyn Griffith-Haynie, CTP, CMC, ACT, MCC, SCAC
Part II of a three-part article in the Sleep Series
Click HERE for Part I

Diagram illustrating the influence of dark-light rhythms on circadian rhythms and related physiology and behavior. (Photo credit: Wikipedia)

The influence of dark-light rhythms on circadian cycles, and related physiology and behavior. (Photo credit: Wikipedia)

Keep in mind:

Time cues are what keep our body clocks aligned with the rest of our 24 hour world.

In order for our sleep-wake timing to cooperate with our planet’s day/night cycle, our biological clock seems to need regular environmental time cues — like sunrise, sunset, and/or a stable sleep-wake routine.

The successful shifting of “native” circadian rhythms to those that coordinate with earth’s 24 hour day is calledentrainment.”

Although light is not the only factor acting on our circadian rhythms, many researchers consider it to be the strongest cue for entrainment. Its entrainment effectiveness, however, can be altered by a number of other factors.

  • Regular exercise, for example, when coupled with appropriately timed light exposure, results in a slightly stronger entrainment response.
  • Certain music and supplemental Melatonin (taken at the right time) have also demonstrated a positive effect on entrainment.
  • Stress, on the other hand, weakens the entrainment effect, as do some medications, nicotine, alcohol (or sudden withdrawal from either)

In the rest of this article, we’ll focus primarily on the mechanisms of light entrainment.

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