Technology is intimately linked with the personal and professional lives of so many, making it hard to remember how new some of the world’s most widespread innovations really are. The first personal computers came out in 1975, the first mobile phone in 1973, and electric light has been on the scene for fewer than 150 years. With this technology comes access to artificial light at all hours—a factor sleep scientists say we are not well-adapted to.
For the vast majority of our evolution, human activity was at the mercy of sunrise and sunset, and our bodies, just like everything else in nature, are set up to work in harmony with this cycle. This biological clock, governed largely by light, is known as our circadian rhythm. It’s also partially mediated by an internal clock, the mechanisms of which are the subject of ongoing research.
Every organism on earth, all the way down to bacteria, has a circadian rhythm—a series of physical, mental, and behavioural changes that approximately follows a 24-hour cycle. Our appetite, energy levels, body temperature, and many other basic functions work according to this schedule.
What does this all have to do with light exposure? Humans and other mammals are wired to respond to natural light. Light signals from your environment hit your optic nerve, which runs from your eyes to a part of your brain called the suprachiasmatic nucleus, or SCN. The SCN then sends signals to other parts of your brain that control hormones, body temperature, and other critical functions.
Unfortunately, backlighting from computer screens and phones, as well as light from LED bulbs (so-called "blue light"), triggers the same reaction as the sun. In other words, when it comes to your circadian rhythm, your brain can’t tell the difference between sunlight and blue light from other sources. (Not so with fire, by the way, which lacks the culpable wavelengths). That’s not a problem during the day, but when your body should be winding down for sleep and is being bombarded with light signals, things tend to go awry. Exposure to blue light delays your body’s production of melatonin, a hormone crucial for sleep.
Over time, chronic disruptions to your circadian rhythm, via late night internet sessions, shift work, or any other cause, are linked with a host of health problems including insomnia, depression, cancer, diabetes, and obesity, to name a few.
Given this, what’s a modern human to do? Short of becoming shut-ins who eschew technology and use exclusively candles and oil lamps after sundown, it seems like we have to fight a losing battle with nature.
The answer is simply to do what you can. If your schedule permits, go to bed around the same time each day. In the evening, use red or orange-toned bulbs instead of LED lights, or ideally, burn candles (they make for better mood-lighting anyway). Do your best to stay away from backlit screens in the evening hours—or if you must, use an app to warm up the light. In the morning, expose yourself to natural light as early as possible to get the cascade of daytime metabolic reactions going and set yourself up for an energetic day.