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How Blue Light and Intensity of Light Impacts Circadian Rhythms

John Bankston John Bankston July 14, 2021
Medically reviewed by Susan Kerrigan, MD and Marianne Madsen

Sleeping used to be simple. People fell asleep shortly after sunset. They awakened with the sunrise. During the day, they worked––often outdoors. If they decided to read or do another activity at night, it was often by the light of a candle or a fireplace. 


Today, fitness apps track and log our sleep patterns. Everything from supplements like melatonin to prescription drugs like Ambien promise uninterrupted slumber. Why? Well, the lightbulb may have been a bright idea but it didn’t do our tired bodies any favors. In the 21st century, we endure a constant assault by artificial blue light thanks to energy-efficient bulbs, laptops, smartphones, and a host of other sources. All of this manmade light has damaged our natural sleep patterns. So if you’re wondering how blue light and intensity of light impacts circadian rhythms, here’s some information along with some tips to reduce its impact.


The Blues Can Make Us Happy


Circadian rhythm is the “physical, mental, and behavioral changes that follow a 24-hour cycle. These natural processes respond primarily to light and dark and affect most living things, including animals, plants, and microbes.” In other words, we are hard-wired to sleep at certain times and wake up at others. Even night owls have a pattern––one inextricably linked with the signals our eyes transmit to our brains. 


There are three types of light-detecting photoreceptors in our retinas. Rods and cones are responsible for most of what we see. Rods are at their best when the light is minimal while cones excel with bright light and are why we can see colors. The third type are the photoreceptive retinal ganglion cells (ipRGCs). These transform light into electrical signals that travel to the part of the brain called the hypothalamus. This action regulates melatonin production––the naturally produced hormone that determines our sleep-wake cycle. These cells are highly affected by blue light–light with blue wavelengths on the short end of the color spectrum. 


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Sleep Tips - Falling Asleep & Circadian Rhythm

Sleep Tips - Falling Asleep & Circadian Rhythm

For most of human existence, there was one steady supplier of blue light: the sun. The electromagnetic radiation it sends toward us can be subdivided into seven colors. In the visible spectrum––what we see when we see a rainbow––blue is the hottest color. It’s also the most damaging to our eyes (just try staring at a blowtorch!). Short-wave blue light with wavelengths between 415 nm and 455 nm has been shown to be the worst for our eyes because it passes right through the cornea and lens to the retina. Besides its connection to everything from dry eyes and cataracts to age-related macular degeneration, blue light gives us a short burst of energy when it stimulates adrenocortical hormone production and taps down melatonin production. This is a major reason why staring at the blue lights emitted by electronic devices during the evening hours can either keep us awake or prevent a fully rested sleep. 


If you’ve ever felt energized during a sunny day, it’s in part because of your body’s hormonal response. Unfortunately, insufficient amounts of natural blue light doesn’t just damage your body’s ability to get a good night’s sleep but can also contribute to mood disorders including anxiety and depression. Indeed, one theory about the sudden rise in those conditions among teens and young adults has less to do with the social media populating smartphones than the artificial blue light emitted by the devices themselves. 


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Sleep Tips - Lights and Temperature

Sleep Tips - Lights and Temperature

More Than Your Laptop


Energy efficiency can have unintended consequences. Energy-efficient buildings, inoperable windows, and recirculated air were shown to be serious disease vectors during the COVID-19 pandemic. Similarly, LED lightbulbs may be better for the environment, but they may not be better for your health. They emit more blue light than traditional incandescent bulbs. So if you’re having trouble sleeping, switching out the LEDs in your bedroom and bathroom is an excellent start. Office fluorescents also emit a high amount of blue light. While you may not be sleeping at work, your health will benefit if you take regular outdoor strolls.  


The best advice is to stow your electronic devices shortly after sunset. If you must use your laptop, desktop, or smartphone, studies show that blue-blocking glasses are effective at protecting your eyes (and your brain) from the damaging light. Whether you choose a nighttime electronics diet or buy a good pair of spectacles, make getting seven solid hours of sleep every night a priority. 

Doctor Profile

John Bankston


John Bankston is a published author of over 150 nonfiction books for children and young adults including biographies of Jonas Salk, Gerhard Domak, and Frederick Banting.

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