Circadian rhythm is a roughly 24-hour daily cycle in the biochemical, physiological or behavioral processes of living beings – from plants and animals to fungi and single-cell cyanobacteria. The term "circadian," coined by pioneer researcher Franz Halberg, comes from the Latin circa "around," and diem or dies, "day," meaning literally "approximately one day."
The formal study of biological temporal rhythms such as daily, tidal, weekly, seasonal, and annual rhythms, is called chronobiology. Circadian rhythms can be trained by external cues. The primary one is daylight. These rhythms allow organisms to anticipate and prepare for precise and regular environmental changes.
The body's circadian rhythm – or the circadian "clock" in humans – is located mainly in the suprachiasmatic nucleus (SCN), which is a group of cells located in the hypothalamus (a portion of the brain). Circadian rhythms are important in determining human sleeping patterns and providing a sleep/wake cycle that allows us to rest, rejuvenate, repair and then re-energize. Basically:
• The natural dimming of sunset triggers our bodies to produce melatonin which causes drowsiness and sleep.
• Increasing sunrise light instructs the body to stop the production of melatonin and thus a wakeful, energized feeling ensues.
Ordinary indoor lighting, indoor living, late night studying, shift work can disrupt the natural signals – making it more difficult to enjoy a good night’s sleep, which is critical to good health and vitality.
Studies show that dawn-dusk simulators can help maintain these natural cycles and thus overall wellness, mental acuity, and energy.
The type of dawn-dusk simulation which NASA tested and now uses to regulate astronauts' sleep patterns uses a "narrow" wavelength of the blue light spectrum (460nm) to naturally help re-set one’s internal clock.
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• As we age, we tend to go to bed earlier, but tend to wake periodically during the night. Using the TwiLight system early in the evening can help you stay up a little later and wake less during the night. That is, the blue light, turned on for 30 to 60 minutes in the evening, helps delay the production of pineal melatonin – so you can stay more alert in the evening hours and experience more restful sleep when the body does produce melatonin later in the sleep cycle.
• A common problem for young people (and many people with illnesses such as chronic fatigue syndrome and fibromyalgia) is that they tend to stay energized until late at night, but then have trouble waking in the morning. For them, using the blue light first thing upon waking can promote greater alertness during the morning, and the onset of sleep earlier in the evening.
Why blue light?
A specialized subset of light-sensitive cells in the retina of the eye – which are thought to have nothing to do with vision – “boast extensions that reach deep into the brain to the hypothalamus, the location of the body’s internal clock,” according to research conducted at Harvard Medical School. These specialized cells appear to convert perception of blue light from the spectrum of natural summer daylight into chemicals such as melatonin (produced by the pineal gland), which change the brain’s “clock settings” and support alertness.
But winter sunlight in most latitudes, and indoor lighting, do not deliver this short wavelength blue light – hence the benefit of blue light therapy. For more information on Harvard’s dawn-dusk simulation research using blue light, see the report “When light has you singing the blues: Blue light resets body rhythms for sounder sleep, higher alertness,” from the Harvard Gazette.
Currently the U.S. National Institutes of Health (NIH) and Harvard sleep medicine researchers are conducting a multi-year trial at Brigham & Women's Hospital in Boston to define more specifically how blue light therapy affects sleep patterns by comparison with other colors of visible light. See "Effects of Different Colors of Light on Human Physiology" for details.
Medical professionals emphasize that people who may have/be at risk for retinal conditions – such as damage caused by glaucoma, macular degeneration, retinal detachment, diabetes – be tested prior to using any bright or blue light therapy, as researchers have found limited evidence that this may cause additional harm.
Note: This information has not been evaluated by the FDA. It is generic and is not meant to prevent, diagnose, treat or cure any illness, condition, or disease. It is very important that you make no change in your healthcare plan or health support regimen without researching and discussing it in collaboration with your professional healthcare team.