The Dark Side of Artificial Light at Night

By Alyse Borkan  |  Jun 24, 2015
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Casper welcomes a contributed post by Ellena Baum, environmental freelance author, as an exploration of the relationship between light, sleep, and our health. She interviewed Dr. Matthew Diamond, MD, PhD, a rehabilitation medicine and sports medicine physician on the faculty at NYU, and the medical director at Misfit, Inc. Misfit makes wearable physical activity and sleep monitors, including the Shine, and smart home devices like a smart, adaptive light bulb called Bolt.

When we go to bed at midnight checking our email, just to wake up at 7am the next morning checking our phone,  a good night’s sleep can be hard to come by. Overwhelming evidence now shows that the risks of poor sleep extend way beyond dragging our feet and reaching for that extra cup of coffee. Light pollution, which has been linked to the disruption of migratory bird patterns, and the absence of a starry sky, is now being connected with poor sleep and a whole host of health issues.

To help understand the relationship between light, sleep, and our health, I spoke with Matthew Diamond, MD, PhD, a rehabilitation medicine and sports medicine physician on the faculty at NYU. Dr. Diamond also serves as the medical director at Misfit, Inc., makers of wearable health monitors and smart home devices that support a healthy lifestyle, like the Shine physical activity and sleep tracker, and a smart adaptive light bulb called Bolt.

“The daily cycle of bright light and darkness present on earth for billions of years has programmed almost all living things with strong biologic responses to light,” said Dr. Diamond.  “But this cycle — our circadian rhythm — is disrupted in today’s industrialized society, where we’re exposed to artificial indoor lighting both during the day and at night.”  He explained that light is a dominant factor in influencing our sleep-wake cycle, and artificial light at night changes our hormonal levels and metabolism and may put us at risk for chronic diseases like diabetes. Surprisingly, it may also increase the risk of cancer.

“There are several hormones that are important for maintaining our health, and even our survival, that are primarily released at night. One of the important hormones released during the deepest stages of sleep is growth hormone, which is essential for our body’s healing and crucial for athletic performance,” said Dr. Diamond.  “Another hormone that is secreted at night is melatonin. Melatonin has the strongest influence on our sleep-wake cycle, and it plays an extremely important role in our metabolism and immune system.  There is increasing evidence that exposure to artificial light at night, which inhibits the production of melatonin and disrupts our sleep cycle, is a significant health hazard.”

The body’s natural secretion of melatonin, which peaks at night, is inhibited by light, and this effect is strongest for blue light. In fact, our physiology has evolved such that the most powerful inhibitor of melatonin is light at a frequency of 480nm, which is the color of a clear blue sky. While exposure to bright light during the day is a healthy reinforcement of our natural circadian rhythm, artificial light at night inhibits the production of melatonin when we need it.

Dr. Diamond explained the epidemiologic evidence.  “A growing body of research suggests a link between exposure to artificial light at night, sleep disruption, and cancer, especially of the breast and prostate.  There are numerous large population studies that show that among women who work night shifts (exposed to more light at night) there is a higher incidence of breast cancer.  Moreover, the risk of breast cancer seems to be directly related to the amount of exposure to artificial light at night.  In fact, those who are blind have a lower incidence of breast cancer, and across the globe the incidence of breast cancer is correlated with the amount of nighttime light as seen by satellite imaging.”

“Evidence of the link between artificial light and cancer is also supported by animal studies,” reported Dr. Diamond.  “Early research with lab animals showed that tumors grow larger and more quickly when animals are exposed to artificial light, rather than darkness, at night.  A more recent landmark study by the cancer researcher Dr. David Blask showed that blood drawn from women at night in the dark was able to stop the growth of human-derived breast cancer cells that he grew in rats, whereas blood taken from these women during the day or at night after light exposure did not slow the growing cancers.  This showed that at night, the blood of these women who were not exposed to artificial light at night, contained powerful inhibitors of cancer growth, which was missing after light exposure.”

The World Health Organization’s International Agency for Research on Cancer has since concluded that shift work that includes circadian disruption is probably carcinogenic to humans, and the American Medical Association has recently taken a strong position on the health hazards of light at night in general.

Does all light have the same effect?

“While light in general suppresses the production of melatonin,” said Dr. Diamond, “blue light has the strongest effect.”  Researchers at Harvard recently showed that exposure to blue light under controlled conditions suppressed melatonin for about twice as long, and shifted circadian rhythms twice as much, as other wavelengths of light.

Another study at Harvard demonstrated that participants who read at night on an iPad, which emits a significant amount of blue light, secreted less melatonin, took longer to fall asleep, had shorter REM sleep, and were more tired the next day, compared to participants who read from a book at night. Some LED light bulbs have the ability to change the color of the light they emit at different times of the day, making it possible to control what light you are exposed to.

So how can you harness the power of light while minimizing its risks? Take control of your light.

Here are some recommendations from Dr. Diamond:

– Try to use only gentle lighting at night.  Light tinted toward the red end of the spectrum is better than blue light at night. If you have to work at night in a setting with light, consider using a light filter or a device or program that limits your exposure to blue light.

– Expose yourself to lots of natural bright light during the day, especially in the morning.  This will help reinforce your circadian rhythm while improving your mood and alertness during day.

– Try to avoid using devices with light-emitting screens (e.g. computer, smartphone, television) for a few hours before bedtime. Although not easy there are countless benefits to unplugging yourself from electronic devices at night.

Misfit has provided a special discount on their Bolt and Beddit products exclusively for Casper readers — click here to use it.


Stevens RG, Zhu Y. Electric light, particularly at night, disrupts human circadian rhythmicity: is that a problem?  Philos Trans R Soc Lond B Biol Sci. 2015 May 5; 370.

Gooley J, Rajaratnam S, Brainard G, Kronauer R, Czeisler C, and Lockley S. Spectral responses of the human circadian system depend on the irradiance and duration of exposure to light.  Sci Transl Med. 2010 May 12; 2(31).

Chang AM, Aeschbach D, Duffy JF, Czeisler CA.  Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proc Natl Acad Sci U S A. 2015 Jan 27;112(4):1232-7.

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