Sleep Timing Disorders & More Laws of Photobiology

More Laws of Photobiology

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

pdclipart.orgLET’S REVIEW what we learned in Parts I and II:

• 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.”

• One of the most important reasons for regulating our sleep schedule is to stabilize the quality of LIGHT to which we are exposed.

• In order for work-arounds (and treatment protocols) for circadian/chronorhythm dysfunctions to be successful, it is helpful to understand and cooperate with what are sometimes referred to as the basic laws of photobiology.

Photobiology is the scientific study of the interactions of light (technically, non-ionizing radiation) and living organisms.” ~ Wikipedia

• Visible Light Regulates — The therapeutic effects of light depends upon the wavelength transmitted to the brain through the eye’s retina — visible light is the primary regulator of the human circadian response.

• Only light that is absorbed will have an effect — and it matters what kind of light is absorbed when.

Visible light is absorbed through through chromophores in the retina.

It “communicates” with the body through two primary pathways to the brain from the retina to the optic nerve: one that governs visual perception and response, and the other that governs “neuro-behavioral” responses, along with hormonal and circadian functions.


• Circadian entrainment is most sensitive to stimulation from light in the blue spectrum, but until 1998, Science had no idea how that happened.

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