Several very recent studies, most notably research from a team headed by Dr. George Brainard at Thomas Jefferson Medical College in Philadelphia, have identified the specific wavelengths of blue light, 446-477nm, that are crucial in suppressing melatonin production in humans.1, 2, 3, 4 As Dr. Brainard notes, “This discovery will have an immediate impact on the therapeutic use of light for treating winter depression and circadian disorders.”
Melatonin, the neurotransmitter that helps us sleep deeply through the night, is produced from serotonin. Suppressing melatonin production raises the levels of serotonin in our brains. This is the key goal of all therapeutic light treatment. This neurological pathway entrains our circadian rhythm to be awake during the day and sleep deeply at night.
Four cells in the human retina capture light and form the visual system. One type, rod cells, regulates night vision. The other three types, called cone cells, control color vision. It’s known that exposure to light at night can disrupt the body’s production of melatonin, which is produced by the pineal gland in the brain and plays a vital role in resetting the body’s biological clock.
Dr. Brainard and his group showed that the combined three-cone system didn’t control the biological effects of light, at least not for melatonin regulation. But subsequent work led to the surprising discovery that a novel receptor was responsible for the effect.
The study looked at the effects of nine different wavelengths of light, from indigo to orange, on 72 healthy volunteers. Subjects were brought into the laboratory at midnight, when melatonin is highest. The subjects’ pupils were dilated and then they were blindfolded for two hours. Blood samples were drawn. Next, each person was exposed to a specific dose of photons of one light for 90 minutes, then another blood sample was drawn. Wavelengths of blue light had the highest potency in causing changes in melatonin levels, he explains.
This research indicates that there is an as yet unidentified photopigment, most sensitive at these wavelengths of blue, which controls these neurological reactions to light. As another researcher notes, this ‘provides the first direct evidence of a non-rod, non-cone photo-receptive system in humans’ – one that is activated by blue light between 420-480nm2.
 Brainard G, Hanifin J, Greeson J, et al (2001) Action Spectrum for Melatonin Regulation in Humans: Evidence for a Novel Circadian Photoreceptor. J. Neurosci (16):6405-6412.
 Thapan K, Arendt J, Skene DJ (2001) An action spectrum for melatonin suppression: evidence for a novel non-rod, non-cone photoreceptor system in humans. J Physiol 535(pt 1): 261-7
 Wright HR, Lack LC (2001) Effect of light wavelength on suppression and phase delay of the melatonin rhythm. Chronobiology International Journal 5:801-8
 Max, M (2001) Molecular Basis of Phototransduction and Circadian Rhythmicity, notes on current research, Dept. of Physiology and Biophysics of Mount Sinai School of Medicine.
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