The Impact of Light (and Dark) On Our Sleep

Read any article on insomnia and how to treat it and you’re likely to see that you should be spending at least some time each day out in the sunlight, and this is definitely true. Our bodies have evolved to respond to the specific wavelengths from the sun so that we are more alert during the day and drowsier at night. But very few of the articles that you read will also tell you about the need to be in the dark. That’s right, just as you need a certain amount of sun exposure, you also need to spend time away from the light so that your body will respond appropriately when you close your eyes. Our circadian rhythms, which are our internal body clocks, are set by the pattern of light and dark that we expose it to every day, and failure to properly expose ourselves to both aspects of day and night can lead to disrupted sleep and insomnia.

Our ability to sleep and to wake up on time is a finely tuned physiological process that is a response to a number of different stimuli, including our exposure to light and dark, our activity levels, what we eat and when we eat it, our body temperature, and many other factors. These control the production of melatonin in our blood stream, and other hormones as well. When everything is working perfectly, the endogenous circadian rhythm that results is a continuous cycle that repeats approximately every 24 hours. It is kept regular by exposure to the sun’s light, as well as the dark. The system has evolved over billions of years, and is present not just in humans but also in other animals and plants around us, including microscopic life.

The human body responds to darkness by lowering its temperature, slowing its metabolism down, and increasing its production of the hormone melatonin. As the sun rises the process is reversed with melatonin production cutting off and the temperature and metabolism increasing. The process is automatic, but studies have shown that when people are kept in total darkness for an extended period of time, the cycle will quickly skew from society’s schedule because it is not an exact 24 hour rotation. It is our exposure to the pattern of sun and darkness that keeps us set to the confines of clock time. Evidence of his has been collected both in studies of people kept in darkness, and in observations of the blind.

The impact of the dark part of our daily cycle is essential to the process. When we are no longer in sunlight, various hormone levels shift. Leptin, a hormone that controls our sense of hunger, increases so that we do not have the urge to eat – if we are not exposed to enough darkness our levels remain low and we will be driven to eat more. Though scientists are not certain as to why this happens, there are theories that suggest that the biological system developed in this way because foraging for food at night would not have been safe for our prehistoric ancestors. The result has been that we essentially fast every night between dinner and breakfast without suffering pangs of hunger.

Studies have shown that those who are awakened in the middle of the night have a tendency to experience hunger pangs and that their leptin levels decrease. Other studies have shown that the entire cycle is controlled by specific genes which are also controlling our metabolism, our immune system and our ability to restore and repair damage to our bodies. When we are awakened during the night, or exposed to light, the genes in charge of this system experience damage and the result can be a number of serious and chronic conditions that endanger our health, including obesity, diabetes, depression and even cancer.

Studies have shown that those who are awakened in the middle of the night have a tendency to experience hunger pangs.

Extensive study has been done on the different types of light that control this cycle, and have found that while the Sun’s light is a blue, short wavelength light, other lights are dimmer and come in long wavelengths of yellow or red. Where the blue light has a strong impact on our circadian rhythms, the others do not. These others are represented in our daily lives by candles, campfires and incandescent lightbulbs. Our electronic devices, such as our televisions, tablets, smart phones and computers, emit the same kind of light as the Sun, and this has proven to be disruptive to the physiological transition that is supposed to take place each night. They have made it harder to fall asleep and to stay asleep, and thrown off our bodies’ schedules.

Technology has brought us many benefits, but scientists are increasingly concerned that since the discovery and harnessing of electricity, we have lost our natural exposure to the pattern of bright, full-spectrum light during the day followed by darkness at night. It has had an impact on our sleep and on our activities at night. Where the nights previously lasted for twelve full hours, we are now only exposed to darkness when we go to bed at night, exposing ourselves to unnatural light for three or four hours per night.

Studies have shown that by removing ourselves from the world of electricity and light, we can reset our internal circadian rhythms in a relatively short period of time, and this may be a good idea for us to do every once in a while. Camping is one of the best ways to accomplish this, though not everybody has access to this activity. One of the best things that we can do to accommodate our need for nature’s original light and dark pattern is to get out into the sunlight during the day and also to sleep in as dark a room at night as possible. It is also a good idea to make sure that the lightbulbs in your home are yellow or red wavelength and that you dim them in the evening hours.