Can Screen Time at Night Disrupt Our Sleep and Circadian Rhythm?

We have all heard the warnings about the harmful effects of blue light from screens, especially before bedtime because it can disrupt and delay our sleep. But is the blue screen light as dangerous as we believe?

According to British circadian and neuroscientist Russell Foster*, the discovery of our biological vision likely sparked the debate surrounding the effects of blue screen light. Our human vision can be divided into two distinct pathways: visual perception and biological vision. While visual perception is crucial for interpreting and navigating the world around us, our biological vision plays a vital role in regulating our circadian rhythm.

Tiny Cells Sparked the Debate

Within our eyes lie microscopic cells known as ipRGC cells. Discovered in the early 2000s, our understanding of these cells is relatively new. What sets them apart is their sole purpose of detecting light, with no involvement in visual perception. These ipRGC cells form the foundation of our biological vision, aiding in the regulation of our circadian rhythm.

The ipRGC cells are particularly sensitive to bright light with blue wavelengths, which is exactly what the sun emits during the day. The sunlight is not only bright but also rich in blue wavelengths. From an evolutionary standpoint, this means that our eyes are designed to interpret daylight and signal to our brain when it is daytime. Therefore, biological perception is a crucial part of our circadian rhythm regulation, however, it is also this perception that has sparked concerns about blue light from screens at night.

Blue Light Tricks the Eye

The narrative surrounding the disruptive blue light emanating from our phones, TVs, and computers likely stems from the knowledge gained through research on our biological vision. Our eyes are indeed sensitive to blue wavelengths, interpreting them as daylight. This has led to the conclusion that the blue light from screens may be detrimental or even harmful at night, as our eyes may misinterpret the light as daylight, keeping us awake.

However, when it comes to the impact of blue light on our wake and sleep cycles, it's not as straightforward as it may seem. While ipRGC cells are indeed sensitive to blue light, they also respond to light of other wavelengths. Therefore, it's not just about whether our screens emit blue light, but also factors like the intensity of the lighting.

Night Mode Is Not a Guarantee of Good Sleep

We often overlook the importance of light intensity when discussing the impact of devices on our sleep. If the light emitted from the screen is strong enough, it almost doesn't matter what colour it is, it can still affect us. This means that the night mode setting on our phones does not necessarily guarantee that the natural sleep preparation which occurs in our bodies in the evening won't be disrupted. If the light intensity is at maximum level, the warm colour tones of night mode may potentially have none to little effect. Therefore, night mode alone cannot ensure good sleep and a stable circadian rhythm; it also depends on the intensity of the light and, more importantly, the content we engage with on our devices.

Entertainment Delays Sleep

Another aspect that is often overlooked when discussing screens and sleep is the content we are exposed to. When it comes to disrupting your sleep and circadian rhythm, it is not just the light emitted by your screen that is the culprit – it is more about the content you are exposed to.

If you start reading emails or news, scrolling through social media, or watching YouTube videos while lying in bed, you're not just exposed to blue or bright light. You're also exposed to a lot of content that stimulates and entertains your brain, keeping you in a wakeful state. When you look at your phone, your brain is activated and not put on autopilot, which is what should happen at night when your body and mind need to reset after a long day.

A Helpful Tip For a Good Night's Sleep

Our devices are not necessarily the big culprits when it comes to light, as it takes a significant amount of blue light to keep us awake. However, using phones and scrolling before sleep can increase our alertness because the content we are exposed to can hinder our ability to fall asleep quickly.

The irony of the whole debate about a good evening routine and screen time is that we often find ourselves in the most illuminated room right before bedtime – the bathroom. Therefore, one can do a lot during the evening by lowering the lighting in the home and avoiding screens before bedtime, but all that effort can often be undone when we go to brush our teeth. The bright light in our bathroom can awaken our body again by lowering our melatonin production and melatonin is an important hormone that signals to our brain that the day is over and it's time for inactivity.

So, a good tip is to minimise all exposure to bright light for 30 minutes before you go to sleep.

*This blog post was inspired by Jesse Chappus' interview with Russell Foster, which you can watch on YouTube.