Sleep is a process, the end result of a day-long series of events occurring both inside and outside the brain. As such, everything you do throughout the day affects the quality of your sleep. Many of these contributors are well-known, such as exercise and stopping one’s caffeine intake. Some are less commonly known, such as blue light exposure.
Blue light is one of the less known but detrimental factors to sleep quality. It tricks your brain into thinking it’s daytime, which results in a cascade of effects that have a negative impact on your physical and mental health. Luckily, there are many options for those who wish to improve the quality of their sleep. Changing up your routine, using specialized software, and donning a pair of stylish spectacles are but a few of the ways to reduce your exposure to blue light.
Winding down the internal clock
“Our bodies, great and complex as they are, have circadian rhythms that require light to tell us when to sleep.”
Many animals, including humans, have an “internal clock.” It tells them when to sleep and, in some cases, even how to navigate the globe. Some animals have more accurate circadian rhythms than others, relying upon mysterious biology to ensure that even blind animals know what time it is. Our bodies, great and complex as they are, have circadian rhythms that require light to tell us when to sleep.
The circadian rhythm is operated by a small part of the hypothalamus, which is located in the center of your brain near the pituitary gland. This is the hormone center of the brain, which decides what to release and when, be it testosterone, serotonin, melatonin, or any other the other various hormones the body needs. Among other signals, the hypothalamus figures out how much light there is from the eyes to figure out what time it is, specifically blue light.
Image: Murgatroyd C and Spengler D (2011) Epigenetics of early child development. Source: Wikimedia Commons
While the light colors of longer wavelengths – such as yellow, orange, or red – have been shown to not have any impact on sleep, blue lights can penetrate your eyelids and flow into your retinas, the thin tissue behind your eyeball that’s primary purpose is to detect light. Blue light is indicative of daytime, as that is when the sky is blue. Through the miracle that is biology, the brain relays this information to the hypothalamus which responds accordingly.
Image: kds4444. Source: Wikimedia Commons
When it is no longer blue outside, the hypothalamus will release 0.7 pg/mL of melatonin at nighttime. (the amount varies throughout the day). This is not an instant process: it takes a couple hours for your brain to adjust. Light colors of longer wavelengths – such as yellow, orange, or red – have been shown to not have any impact on sleep. Science has clearly shown that the color of light has a major impact on sleep. But why is this important? What’s changed?
Natural lighting at unnatural times
“It is widely agreed that both blue light and circadian rhythm disruptions have detrimental effects on sleep.”
The hypothalamus is not very versatile and cannot differentiate one light source from another. So long as the light has the same color – and therefore the same wavelength – it will assume that it is its corresponding time of day. If the light is blue, the brain will assume it is daytime; if it is yellow, it will assume it is the afternoon. For the most of human existence, this has been perfectly adequate at keeping humans sleepy when they should be (although night workers may disagree).
For almost all of earth’s history, the daytime sky was the only source of blue light. When it grew dark, humans may have lit campfires to gather around or lanterns to see by, but these sources released yellow light akin to a sunset. This did not bother the hypothalamus, which ran just as smoothly as always.
Then, all of a sudden, the world became filled to the brim with blue light. Streetlights are now being fitted with LED bulbs, which produce blue light. People spend hours of their day looking into the glass screens of cellphones, televisions, and computer monitors, all of which release blue light. Screens often incorporate LED into their displays, which are brighter, have more depth in color, and are more energy efficient. To the simple hypothalamus, which cannot differentiate between the sky and the screen, it is always daytime. Even when you are lying in bed around midnight, reading the news on your phone or texting your distant friend “good night,” your brain thinks that it is daytime.
This disrupts the circadian cycle greatly, which can result in insomnia, less REM sleep, and all of the consequences that ensue. As the constant bombardment of blue light makes your brain think it is daytime, the 24-hour cycle that the hypothalamus relies upon becomes desynchronized. This not only affects one’s ability to sleep, it can also contribute to mood disorders such as depression, anxiety, and even bipolar disorder.
Many studies have shown this to be true, and there are other disruptive circumstances that further prove how these disruptions contribute to insomnia. For example, seasonal affective disorder, wherein sufferers experience mood swings during autumn and winter, is largely caused by the lessening of light levels during the colder months. Shift workers, who often work at irregular hours, have disproportionate rates of insomnia and depression due to the interruption of their natural circadian rhythm. Jet lag, which occurs when one rapidly changes time zones via air travel, is another manifestation of an interruption to circadian rhythm. These disruptions affect sleep quality almost immediately, as anyone who