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The Effects of Continuous Light on Humans

Evidence is mounting that continuous and extended exposure to light, as opposed to having the completely dark evenings and nights we evolved with, has ill effects on human health that we were unaware of until recently. There haven't been any studies on humans where subjects are exposed to light continuously for days on end (this would be unethical), but many have been done on animals that indicate that at least a few hours of total darkness are necessary for optimal health. The problem is that light hitting the retina of the eye, even through a closed eyelid, inhibits the body's production of melatonin, a hormone that is responsible for good sleep, the production of other hormones and a host of other necessary functions.

  1. Sleep Disorders

    • According to George Brainard, a professor of neurology at Jefferson Medical College, exposure to light during the night can disrupt the body's circadian rhythms (which tell us when it's time to sleep and when to wake), which are driven in large part by melatonin production. This can result in a range of sleep disorders including not only insomnia, but delayed sleep-phase disorder as well, where someone can only fall asleep very late at night---then has difficulty being fully awake in time for work or school.

    Breast Cancer

    • In addition, inhibited melatonin production appears to place women at unnaturally high risk for developing breast cancer. The Journal of the National Cancer Institute reports a study linking increased exposure to light at night to increased rates of breast cancer. Apparently, women who consistently work night shifts, such as flight attendants and factory workers, are up to 35 percent more likely to get breast cancer---and blind women, whose melatonin levels aren't affected by light at all, have up to 50 percent lower breast cancer rates.

    Melatonin and Autism

    • According to Dr. Jaak Panksepp, a psychobiologist and neurologist at Bowling Green State University, there is evidence suggesting a link between low melatonin levels and autism. Relatively little research has been carried out in this area so far.

    Environmental Effects

    • Of course, humans are not the only living beings affected by constant or high exposure to light. Birds are too, as is plant life. Migrating birds are often disoriented by nighttime light sources and sometimes crash, fatally. And another, seemingly more benign effect of overlighting is the overgrowth of algae blooms on freshwater surfaces---this can not only lower drinking water quality for humans and other animals, but can throw the ecosystem of the pond or lake out of whack (which can ultimately also affect human food sources).

    What You Can Do About It

    • One of the most effective ways to avoid overextended exposure to light is to sleep in a completely dark room. This can be achieved by pulling heavy, dark curtains or shades (professionally called "blackout" shades) over your windows at night, and turning off any and all sources of artificial light within the room. It is also a good idea to avoid night-shift work if possible, since it requires sleeping during the day, when it's difficult to achieve complete darkness. It is probably a good idea to avoid staying up extremely late on a regular basis, for that again shortens the amount of time you are likely to be able to sleep in complete darkness.

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