Privacy Policy User Agreement Contact Us
  Extended Search

Current Issue
Submission Guidelines
Important Research
ND Calendar
ND Update
Nutrition and Herbs
ND Locator
Reader Poll
Schools & Associations
Consumer Information
Contact Us
Link To Us
Site Map

Blue Light Special

By Jacob Schor, ND

"The day is an epitome of the year. The night is the winter, the morning and evening are the spring and fall, and the noon is the summer."

– Henry David Thoreau

I had a peculiar interaction early one morning as I jogged across City Park Golf Course. It was just past sunrise. A man walking across the greens stopped me with a question. Dressed neatly in an older suit and white shirt and carrying a small nylon backpack, he looked to be about 50, respectable and quite out of place. His speech was slightly accented, as if English wasn't his native language. He greeted me and asked whether I knew the time of day. I wasn't wearing a watch but estimated it was about 6:45a.m..

I had misunderstood him. He clarified, "No, is this morning or evening?"

I told him, "Morning."

With a burst of anger, he whispered "Damn it," turned and walked off.

This encounter stands out in memory as I've made up countless scenarios to explain why this man could have been so lost in time. It was just past sunrise. The sun was close enough to the eastern horizon that it was visibly moving up, not setting. In the years since this encounter, a number of interesting studies have been published that explain how the brain knows the time of day just from the frequencies of light that it perceives. This is interesting enough stuff that I'm going to try and explain it, even though it may seem a trifle tedious. The bottom line, once we understand it, is fascinating.

Nevertheless, that golf course encounter seems even more inexplicable.

Ever since the 1850s when Mueller identified the rods and the cones in the retina of the eye as photoreceptors, it was believed these were the only the light-sensing receptors in the eye. This doctrine collapsed in 2001 as a result of work done by Debra Skene.

Skene and her colleagues at the University of Surrey tested whether some wavelengths of light had greater effect than others at suppressing melatonin. They shone light into 22 people's eyes in the middle of the night, when melatonin levels are highest. Melatonin production was clearly sensitive to light and less was made as light intensity increased. Testing the relative effect of different wavelengths of light produced a surprising result. The shortest wavelengths, what we see as dark blue, caused the greatest drop in melatonin.

The rods and the cones of the retina barely detect this wavelength of light. Skene concluded that a third, still-unknown type of photoreceptor was present in the eyes, which tells the brain when to stop making melatonin.

The following year, David Berson of Brown University successfully isolated these new photoreceptors and described them as a type of retinal ganglion cell. These cells extend long projections into a part of the brain called the suprachiasmatic nucleus (SCN) so they can transmit information directly from the eyes. This is the region of the brain that regulates the circadian clock; the body's internal timer that tells all the organs and even individual cells what time it is. Berson originally isolated these cells in animals but correctly predicted they play the same role in people, controlling release of melatonin.

This is a big thing. Up until now, we thought our eyes were only for seeing. In fact, there are two completely separate systems in operation in our eyes. One, using rods and cones, allows us to see things, the second, using Berson's ganglia tells us what time it is.

In 2003, Lockley et al. confirmed these shorter wavelengths of light have a greater effect. The short 460-nm wavelengths of light suppress melatonin twice as much as the longer, 555-nm light – the wavelength best seen by the human eye.

This is useful knowledge. Ever since Edison invented the light bulb, we have inadvertently been offsetting our internal clocks by using artificial lighting. Controlling which wavelengths of light reach the eye gives us a way to reset and control our internal clocks. It also has opened up the possibility of simple treatments for some unexpected conditions.

In the March 2005 issue of the Journal of Clinical Endocrinology & Metabolism, Christian Cajochen reported success at resetting the circadian clock of test subjects by using colored lights. He and his colleagues had nine male volunteers spend an evening and night in a room in which the researchers controlled the lights. In separate rounds, these volunteers were exposed to indigo-blue light with a wavelength of 460 nanometers, green-yellow light with a wavelength of 550 nm, or complete darkness. Throughout the experiment, the researchers monitored each subject's daily sleep-wake cycle.

Volunteers in total darkness during the two-hour period displayed normal nighttime trends, including reduced core-body temperatures, slower heart rates, elevated melatonin concentrations in saliva and increased sleepiness. However, exposing subjects to blue light suppressed those changes, while green-yellow light had a minimal effect.

I think of this as I walk the dog at night and see the blue-lit house windows illuminated from the television sets in the neighborhood. How much of our ability to watch late night TV is connected with that blue?

It was made clear in another recent research paper that there are two, separate, functional light-sensing systems in the eye; one for vision and one for clock setting. About 5 percent of blind people who lack rods and cones in their eyes still have functional blue-light sensitive ganglia and their eyes can perceive light needed to set the body's clock. The results of experiments using blind people lacking rods and cones appeared in a 2007 issue of Current Biology. Neither of the two people who took part could see, yet they unconsciously sensed whether it was light or dark by detecting blue light. Farhan Zaidi collaborated with doctors in both Britain and in Boston to find suitable subjects. By shining a light into their eyes, the researchers were able to delay the subjects' body clock cycle, proving that their ganglion cells still registered light. Light caused melatonin to drop by 60 percent while alertness sharpened and brain activity increased, demonstrating that the body clock had been fooled into thinking it was daytime.

"I do not say that John or Jonathan will realize all this; but such is the character of that morrow which mere lapse of time can never make to dawn. The light which puts out our eyes is darkness to us. Only that day dawns to which we are awake. There is more day to dawn. The sun is but a morning star."

– Henry David Thoreau

Some of the potential applications of this knowledge are obvious. Strengthening the circadian rhythm should help with insomnia. Avoiding suppression of melatonin by adjusting nighttime light frequencies could lower risk of certain cancers. Some applications are less obvious.

Teenagers and their peculiar sleep habits were one of the first applications I read about. Anyone who has lived with a teenager will testify they have little or no sense of when it is bedtime and tend to stay up way too late. Experts say teens need nine hours of sleep a night, but less than 20 percent get this much. The U.S. National Sleep Foundation tells us that 25 percent of teens fall asleep in class at least once a week.

Mary Carskadon from Brown Medical School says about half of the teenagers she tested actually show symptoms of narcolepsy. She found many teens drop immediately into rapid eye movement (REM) sleep, skipping over the first stages of nonrapid eye movement sleep (NREM), a distinct symptom of narcolepsy.

We need light in the morning and then darkness in the evening to set our circadian clocks. Kids go straight to school after waking, at times so early that much of the year it still is dark. They don't see natural sunlight until late in the day, if they do at all. A well-lit classroom is illuminated at about 400 lux. Compare that to the 10,000 lux experienced outdoors on a dull, rainy day or the more than 100,000 lux experienced on a bright day. Is it any wonder kids don't know when to go to sleep?

That wavelength of 480 nanometers to which the retinal ganglia are so sensitive is in the blue spectrum. In fact, it is pretty much the color of the sky on a bright sunny day. This knowledge has triggered some interesting attempts to reset circadian rhythms.

Mariana Figueiro at the Lighting Research Center at Rensselaer Polytechnic Institute in New York proposed using orange-tinted glasses and light boxes as therapy for tired teens a few years back. Her idea was to expose the kids to the right kind of light at the right time of day to bring their sleep cycles back in line. Orange glasses used in the evening can filter out blue light and prevent melatonin suppression. Light boxes with blue LEDs used in the morning can suppress melatonin and wake the kids up.

In a March 2008 paper, Figueiro came up with another interesting idea. She proposed that gas stations and truck stops purposely use blue lighting to wake up drivers and reduce highway accidents. She suggests that truckers take 30 minute "light baths" during the night to keep alert while driving. She is currently testing whether illuminating the interiors of truck cabs with blue LED lights is feasible.

It's not just teenagers who have chronic sleep problems. Old people can have as much trouble sleeping at the correct time of day as teenagers. Older patients tell me they can't sleep through the night but must nap during the day. In a New Scientist interview, Russell Foster at Imperial College London pointed out one possible explanation for this: "In old age, the lens and cornea of the eye start to yellow, which means the eye filters out the blue light needed to set their circadian rhythm."

Certain types of dementia, including Alzheimer's, cause a loss of neurons in the suprachiasmatic nucleus (SCN); the part of the brain that controls the circadian clock and sleep. As a result, the internal clock for those with Alzheimer's may be off by several hours, leaving them too awake at night. Thinking that this might be a sort of "use it or lose it" scenario, a Dutch researcher tried stimulating the deteriorating brains of senile rats with light. Eus van Someren from the Netherlands Institute for Brain Research exposed old rats that had SCN cell deterioration and sleep disturbances to bright light and found their sleep patterns became healthy and the SCN neurons were reactivated.

Researchers have tried similar approaches with people. Ancoli-Israel et al. in the American Journal of Geriatrics reported a nursing home experiment. Seventy-seven residents, average age of 86, were assigned to one of four treatments: evening bright light, morning bright light, daytime sleep restriction or evening dim red light. In just 10 days of treatment, "increasing exposure to morning bright light delayed the acrophase of the activity rhythm and made the circadian rhythm more robust."

That Dutch fellow, van Someran, and a number of California researchers tried this same kind of approach on 46 people with Alzheimer's disease. Half sat in bright light at 2,500 lux for an hour every morning, while the controls experienced the usual 150- to 200-lux illumination. After 10 weeks, the exposure to the bright light had significantly improved the rest and activity rhythms in the most severely affected patients. The research used plain broad-spectrum light and not the short-wavelength blue lights we now know are most effective. The results of a similar study by the same researchers were published in February 2008. In this trial they used the same bright light in the morning along with a 5-mg dose of melatonin at bedtime and achieved even better results.

Suggesting a patient sit outside in bright sunlight sounds remarkably old fashioned – almost something a naturopath might suggest. Bright lights, especially blue lights, tell our brains it is morning. An equally interesting strategy is being used to convince the brain it is night. Tints have been developed that filter out the specific wavelengths of blue light that suppress melatonin. These are used to tint light bulbs, computer and TV screens, and especially glasses. Using these tinted glasses and other filters prevents the nighttime suppression of melatonin that is ubiquitous and blamed for a number of health problems.

The most intriguing paper I have come across so far is one on bipolar disorder James Phelps, writing in a recent issue of Medical Hypothesis, combines this knowledge of the retinal ganglia with past research on what is called "dark therapy" for treating bipolar disorder. In 1998, Wehr et al. suggested, "Fostering sleep and stabilizing its timing by scheduling regular nightly periods of enforced bed rest in the dark may help to prevent mania and rapid cycling in bipolar patients." A 1999 paper describes a case history in which this dark therapy was successfully used to treat a rapidly cycling bipolar patient. A 2005 paper in Bipolar Disorders confirmed the idea "that extended bed rest and darkness could stabilize mood swings in rapid cycling bipolar patients." Forcing patients to live in darkened rooms is apparently difficult outside of an inpatient setting. Phelps theorizes that a similar effect to dark therapy can be achieved simply by wearing yellow-tinted glasses that filter out blue light in the evening. He reports success with several patients.

Of course, if filtering out blue light is useful for treating bipolar disorder, a troubling question quickly arises. Could our increased evening exposure to blue light emanating from fluorescent lighting, televisions and computer screens account for the incidence of bipolar disorders in adults, and especially in children? We have also assumed that the explanation of why certain disease incidence increases with latitude is less UV exposure and consequently a greater chance of vitamin D deficiency. Another possible explanation is that at higher latitudes, people depend on artificial lighting for more of the year.

Other suggested uses for these blue-light filtering glasses include treating insomnia (of course), infertility and depression. Another condition, fibromyalgia, also comes to mind because it is generally accompanied by significant sleep disturbances. Although I've seen no published evidence yet, suggesting these blue-blocking lenses for this patient group seems reasonable.

"The true harvest of my daily life is somewhat as intangible and indescribable as the tints of morning or evening. It is a little star-dust caught, a segment of the rainbow which I have clutched."

– Henry David Thoreau, Walden


  1. Thapan K, Arendt J, Skene DJ. An action spectrum for melatonin suppression: evidence for a novel non-rod, non-cone photoreceptor system in humans. J Physiol. 2001 Aug 15;535(Pt 1):261-7.
  2. Make light of jet lag. New Scientist, 2002 Feb 16;2330:17.
  3. Berson DM. Strange vision: ganglion cells as circadian photoreceptors. Trends Neurosci. 2003 Jun;26(6):314-20.
  4. Brown RL, Robinson PR. Melanopsin: shedding light on the elusive circadian photopigment. Chronobiol Int. 2004 Mar;21(2):189-204.
  5. Lockley SW, Brainard GC, Czeisler CA. High sensitivity of the human circadian melatonin rhythm to resetting by short wavelength light. J Clin Endocrinol Metab. 2003 Sep;88(9):4502-5.
  6. Cajochen C, M√ľnch M, Kobialka S, et al. High sensitivity of human melatonin, alertness, thermoregulation, and heart rate to short wavelength light. J Clin Endocrinol Metab. 2005 Mar;90(3):1311-6.
  7. Blind people "see" sunrise and sunset. New Scientist. 2007 Dec 26; 2635:9.
  8. Zaidi FH, Hull JT, Peirson SN, et al. Short-wavelength light sensitivity of circadian, pupillary, and visual awareness in humans lacking an outer retina. Curr Biol. 2007 Dec 18;17(24):2122-8.
  9. Teenagers: Lost in Time. New Scientist. 2006 Sept 2;2567:40-3.
  10. Private communication April 7, 2008
  11. Blue LEDS could rouse sleepy drivers. I. 2008 March 29;2649 :23.
  12. Figueiro MG. Light isn't just for vision anymore: implications for transportation safety. Lighting Research Center, Rensselaer Polytechnic Institute.
  13. Lucassen PJ, van Someren EJ, Swaab DF. [Are active neurons a better defense against aging in Alzheimer's disease?] [Article in Dutch] Tijdschr Gerontol Geriatr. 1998 Aug;29(4):177-84.
  14. Ancoli-Israel S, Martin JL, Kripke DF, et al. Effect of light treatment on sleep and circadian rhythms in demented nursing home patients. J Am Geriatr Soc. 2002 Feb;50(2):282-9.
  15. Dowling GA, Hubbard EM, Mastick J, et al. Effect of morning bright light treatment for rest-activity disruption in institutionalized patients with severe Alzheimer's disease. Int Psychogeriatr. 2005 Jun;17(2):221-36.
  16. Dowling GA, Burr RL, Van Someren EJ, et al. Melatonin and bright-light treatment for rest-activity disruption in institutionalized patients with Alzheimer's disease. J Am Geriatr Soc. 2008 Feb;56(2):239-46.
  17. Wehr TA, Turner EH, Shimada JM, et al. Treatment of rapidly cycling bipolar patient by using extended bed rest and darkness to stabilize the timing and duration of sleep. Biol Psychiatry. 1998 Jun 1;43(11):822-8.
  18. Wirz-Justice A, Quinto C, Cajochen C, et al. A rapid-cycling bipolar patient treated with long nights, bedrest, and light. Biol Psychiatry. 1999 Apr 15;45(8):1075-7.
  19. Barbini B, Benedetti F, Colombo C, et al. Dark therapy for mania: a pilot study. Bipolar Disord. 2005 Feb;7(1):98-101.

About the Author: Dr. Jacob Schor graduated with a bachelor of science degree from Cornell University and received his naturopathic training at National College of Naturopathic Medicine. He currently practices at the Denver Naturopathic Clinic. E-mail Dr. Schor at

Archives | Contributors | Current Issue
Important Research | Naturopathy Calendar | ND Online | Nutrition & Herbs
ND Locator | Reader Poll | Schools & Associations | Submission Guidelines
Consumer Information | Contact Us | Link To Us | Site Map

Other MPA Media Sites:
ChiroWeb | AcupunctureToday | MassageToday | DynamicChiropractic | DynamicChiropractic Canada
ChiroFind | ToYourHealth | ChiropracticResearchReview | NutritionalWellness | SpaTherapy

User Agreement | Privacy Policy

All Rights Reserved, Naturopathy Digest, 2011.
Date Last Modified - Friday, 17-Oct-2008 12:11:15 PDT