Adults and children are spending more and more time in front of screens which emit blue light. How does the blue light from our devices differ from daylight, and how does that affect our sleep? What controls the circadian rhythm and is this blue light dangerous? These are just some of the topics we will cover.
As biological creatures, we are controlled by a built-in internal clock that regulates when we are active and when we are at rest. It's based on the daily periods of light and darkness which are affected by the Earth's rotation. Our body temperature and our hormone levels vary at different times of the day, as does our need for food and sleep. There are some variations in this circadian rhythm from person to person - some are early risers while others are night owls. It's well-known that humans and animals are controlled by the circadian rhythm, but in 2017 a group of researchers was awarded the Nobel Prize in Medicine for discovering exactly how this inner clock functions.
The American researchers were able to show that all biological creatures are ruled by their circadian rhythm down to the cellular level. The researchers discovered that a gene in fruit flies codes for a protein which builds up during the night and is broken down during the day. They found several proteins whose functions combine to form our inner circadian clock. Although their studies were on fruit flies, further research has shown that the same function exists in the vast majority of living beings and organisms on Earth. In this way we have evolved to live according to the patterns of day and night. Maybe you've seen how certain flowers open up in the daylight and close when it gets dark in the evening. This is a sign of their circadian rhythm.
The discovery of the circadian clock has led to a completely new perspective on our connection to daylight, circadian rhythm and the changing seasons. If our circadian rhythm is disturbed by factors such as prolonged shift work, irregular habits or severe sleep problems, there can be negative consequences for our health. The risk for developing certain health issues can increase, such as diabetes, mental illness and becoming overweight.
As you're probably aware, daylight is very important to us because it makes us feel more alert and awake, improves our mood and affects how we sleep. That's why it's not uncommon for us to feel more tired and unmotivated during the winter months when we don't get as much daylight.
Daylight also controls the secretion of the sleep hormone melatonin and the feel-good hormone serotonin.
The sleep hormone melatonin is produced in the pituitary gland of the brain and helps regulate the circadian rhythm. When it's light outside, production of melatonin increases, so the body understands that it's time to sleep. This process is called ”Dim light melatonin onset” or 'DLMO' and defines the start of melatonin production. The natural twilight light is a clear signal for the circadian clock. However, the blue light from electronic screens is thought to inhibit the secretion of melatonin because the brain is fooled by the blue light and this then confuses the circadian clock.
The neurotransmitter serotonin is a happiness hormone that affects our mood and makes us feel good. 90% of this hormone is found in the stomach and intestines and the rest in the central nervous system. Melatonin makes us sleepy, and serotonin makes us alert. Serotonin release is also stimulated by sunlight and a deficiency can contribute to sleep problems.
Natural light improves mood and makes us feel more awake and well compared to electrical light from screens, according to research. The intensity of daylight also changes all the time during the day and follows the seasons, which is not the case with electric light. Natural daylight is also much stronger than ordinary indoor lighting. According to recommendations, indoor office lighting should be around 500 lux. That is still only half as strong as the daylight your skin is exposed to outdoors on a cloudy winter's day. Even that is barely comparable to the light on a sunny summer's day, which can reach up to around 100,000 lux.
That's why it's becoming more and more important to take advantage of daylight, even indoors. When new offices and residential buildings are built, the availability of natural daylight is important. It's measured both by daylight factor (the amount of daylight indoors), and daylight autonomy, which is a measure of how much time in one year the surface is lit by daylight of a certain intensity.
Until recently, we spent most of our time outdoors, being active in daylight and then resting by a fire or a candle before going to bed. Nowadays, we spend more and more time indoors with electric light, whether it's working at a computer or looking at a phone or tablet. We don't absorb anywhere near as much daylight, which tricks the brain into thinking that the day is much longer when we spend the evenings in front of various electronic screens. The electric light delays our sleep and causes a shift in the circadian rhythm.
Both our bodies and the brains are synchronised with the sun. When it's bright outside we are alert and awake and when the sun goes down we become sleepy. If the light changes, our inner clock can become confused and we find it difficult to sleep or stay awake. The most common example is the jetlag that results from travelling between time zones. Your body is used to falling asleep at a certain time, but even though it's still bright outside in the new time zone, you can't keep your eyes open. It usually takes at least a couple of days for the body and brain to adapt to the new time.
Light is made up of electromagnetic particles that move in waves. Blue light is the short light waves found in sunlight. Different light comes in different wavelengths and blue light has a wavelength of between 400 and 450 nanometres. The lower the wavelength, the higher the energy. Natural blue light makes us energised and alert and that's how we feel when we spend time outdoors during the day. That helps regulate our circadian rhythm.
Blue light is also the light that comes from our electronic screens. Because we spend a lot of time in front of the screens with the blue light that makes us alert, our circadian rhythm and our sleep cycles can be disrupted. The body is tricked into thinking that it's still light and the secretion of melatonin that makes us sleepy is delayed. To look at it from a pessimistic point of view, in the modern world we're spending more and more time in a kind of half-day: indoors during the day and then in front of our screens at night.
Most studies show that we become more alert from the blue light found in sunlight and our electronic devices. The light delays the secretion of melatonin and if we use our devices late in the evening, there is a risk of poor sleep and a disrupted circadian rhythm.
For example, the LAN theory, or Light-at-night theory, concludes that light exposure at night lowers melatonin production. The stronger the exposure, the lower the level of melatonin secretion and that affects the sleep cycle.
However, further research into this topic disagrees with the theory. In some cases, only a small effect has been observed and this may be due to a so-called photo history where how much daylight you get during the day reduces the effects of light exposure later in the evening.
Researchers in Manchester, for example, found by experimenting on mice that the blue light was not a significant problem. They showed that it's more similar to the light present during twilight, which humans are already used to. However, more yellow light tones in the evenings confuses the brain to a greater degree. However, the experiments were performed on mice, which does not guarantee that they would have the same effect on humans.
As society has developed, we live in densely lit buildings more and more often. Lots of us spend a large part of our days indoors in front of screens in an office environment and when we get home we spend most of the evening in front of the TV, tablet, telephone, possibly even using several screens at the same time. We are exposed to natural daylight less and less and more and more to electric light. This applies to both children and adults. In addition, we are affected by all the dramatic events we see on our screens, whether that's video games, exciting TV series or provocative posts on Twitter. The adrenaline production in the body rises and it gets more difficult to relax and go to sleep.
Despite society's increasing reliance on screens and screen time, there are things you can do to improve your sleep quality.
Turn off your phone and other devices one hour before bedtime so that your body will have time to get used to the natural darkness. If your brain still needs stimulation, you can read, write down your thoughts from the day, or listen to an audiobook or podcast.
Lower the brightness on your phone and turn on night mode. This makes the colours on your phone's screen warmer and more yellow. On many new phones this is an existing setting that automatically adapts to the time of day, depending on which part of the world you're in, and changes the screen brightness.
The process of getting a good night's sleep begins during the day. If you want to sleep better make sure you get enough daylight outside during the day. Exercising outdoors doesn't just tire out your body, it also decreases stress and increases endorphins. Other outdoor activities like days out, working in the garden or walks are also beneficial for your health and quality of sleep.
If you have problems sleeping, it might be worth trying to keep to a sleep schedule. They are especially popular for helping young children sleep better. The idea is to eat, be active, rest and sleep at the same time every day as much as possible. Your body and brain will appreciate the predictability and your sleep will improve.
https://www.health.harvard.edu/staying-healthy/blue-light-has-a-dark-side https://www.theatlantic.com/health/archive/2012/03/your-bodys-internal-clock-and-how-it-affects-your-overall-health/254518/ https://www.cincinnatichildrens.org/news/release/2020/light-sensing-cells https://time.com/5752454/blue-light-sleep/
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