Since the invention of the light bulb, we no longer depend on the natural light of the Sun for our main activities.
Today, more than ever, many people spend most of their day not only in artificially lit rooms, but also in front of a display (smartphone, PC, TV). Recently, there have been several studies expressing concerns about the fact that looking at bright screens in the evening can upset our circadian rhythm, the internal clock that regulates our sleep-wake cycle.
This means that watching a display before bed makes it harder to fall asleep.
There are many products that filter out blue light on displays, promising to improve the quality of the sonno. Do they really work?
Is it really that simple? If screen light changes our circadian rhythm, just filter it to solve the problem? Things are more complicated than that.
How does the circadian rhythm work?
The circadian rhythm is an innate “biological clock” found in many life forms, including plants, fungi, and animals. In humans, the biological clock is located in the hypothalamus.
The hypothalamus releases a hormone called melatonin. Melatonin is often referred to as the “sleep hormone” because its levels are high at night but drop just before waking in the morning. The clock has an inherent rhythm, but can also be adjusted in response to light.
Is technology changing our circadian rhythm?
Professor John Axelsson, sleep research expert at the Karolinska Institute, explains: “our internal clock follows an intrinsic circadian rhythm of almost 24 hours. It is very sensitive to light around dusk and dawn, and this allows our systems to be dynamic and adapt to seasonal changes in day and night length.”
Many aspects of modern technology, from the basic light bulb to the brand new touchscreen phone, emit light. Professor Jamie Zeitzer of Stanford University says: “Light does two main things to the clock. Set the time of the clock and change the amplitude or strength of the clock.”
As our circadian rhythm changes melatonin levels, we can look at levels of this “sleep hormone” to see what is disrupting our body clock.
And what we see is not clear. Several studies have shown that intense and artificial light suppresses the production of melatonin in humans.
Good light and bad light for the circadian rhythm
Interestingly, very bright artificial light is actually also used for phototherapy, which helps people with very off-kilter body clocks wake up and fall asleep sooner.
The intensity of the light used for phototherapy is much higher than that emitted by any screens or light bulbs we use.
A study (from 2014) looked at a more realistic scenario: comparing melatonin levels and sleep quality of people who read a regular book or ebook before bed. They found that participants with the ebook had reduced melatonin levels.
Doctor Cele Richardson from Western Australia University says: “There is evidence that 1,5 hours (or more) of screen use reduces the natural nocturnal increase in melatonin, and this effect is exacerbated over multiple nights.”
Importantly, “however, this does not appear to translate into how long it takes to fall asleep.”
What does this mean for our sleep patterns?
Although we know that melatonin has many effects on the body and is associated with the circadian rhythm, we don't know exactly how and how much reduced melatonin affects our sleep quality.
There are many studies that look at technology use and sleep quality or the time it takes to fall asleep. Many of these find a correlation between screen time and sleep, but these are weak correlations. They don't show that increased screen time causes sleep problems.
The 2014 study I cited found that on average paper book readers fell asleep 10 minutes earlier than ebook readers. Other studies have compared people who use display filters to regular users. Here the difference noted is only 3-4 minutes in the time it takes to fall asleep.
So many variables
Since sleep is influenced by many factors, it is often difficult to ensure that it is only the effect of time spent in front of a display.
A bidirectional relationship between technology and sleep is also likely. Yes, technology use can affect sleep over time, but technology can also be the effect of sleep problems. People who have trouble sleeping may subsequently increase their use of technology.
A summary, at the moment, is lapidary:
technology, especially that involving artificial light, changes our circadian rhythm.
We know this because there are definitely differences in melatonin levels after using the display.
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