Ask anyone for advice on how to improve your sleep, and one of the first things they’ll usually say is to stay off your phone before bed. 

Reducing our exposure to blue light has become standard ‘sleep hygiene’ advice – the idea being that the light from our phones, laptop screens and TVs messes with the production of the sleep hormone melatonin, leading to a disruption to our internal body clock.

But according to a new study, that might not be the case – or at least, it might not be as big a deal as it’s made out to be. The research, which was carried out by a team at the University of Basel, Switzerland, found that no single colour of light (along the blue-yellow axis) was any more disruptive than another when it comes to sleep. 

It also puts forward the idea that the overall brightness of the light we’re exposed to likely plays a larger role in disrupting our internal clock or circadian rhythm.

The findings, which were published in the journal Nature Human Behaviour, suggest that dimming the lights around us – whether that’s our phone screens, overhead lights or bedside lamps – could help to prevent a disruption to our sleep hormones, positively impacting sleep as a result.  

To find out how various types and intensities of light could potentially affect sleep, the research team recruited 16 participants who were exposed to three different light ‘scenarios’: a plain white control light, a yellow light and a blue light. The participants were exposed to these lights for an hour, starting 30 minutes after their habitual bedtime, ie the time when they’d usually start to get sleepy.

While you might expect the blue light to be particularly disruptive, the study reports there was “no conclusive evidence” that changes in light colour played a role in preventing sleep. In fact, they said there was “conclusive evidence” that different colours of light did not suppress melatonin differently. Instead, they found that all three types of light did delay the onset of sleep, suggesting that it was the light itself, as opposed to the colours, that made a difference to the participants’ body clocks. 

Being exposed to any form of bright light before bed has the potential to mess with our sleep due to specialised cells that sit within our retina – the light-sensitive tissue that sits at the back of the eyeball.

These cells are known as ‘ganglion cells’, and they play a role in the sleep-wake cycle because they’re designed to detect light intensity, so they help us to discern when it’s day or night.

Ganglion cells are a type of photoreceptor – basically, a cell that helps us see. The other two photoreceptors in the eye are rods and cones, and these both convert light that comes into the eye into electrical signals which pass to the brain, where they’re used to provide vision. 

It’s the cones, in particular, which help to detect colour (the rods are used to help us see in low-density light, so they’re not relevant here). In this study, the researchers made sure that all three light sources affected the ganglion cells in the same way, so they could measure solely how the colours being processed by the cones did or didn’t affect the sleep-wake cycle.

The lack of evidence that the colours made a difference – paired with the fact that the participants did experience some delay in their sleep – suggests that the way all three lights interacted with the ganglion cells is likely responsible for the disruption they experienced. 

This study isn’t an invitation to spend hours scrolling on your phone before bed, if that’s what you were hoping. Scrolling on your phone can also be disruptive for other reasons – doomscrolling, for example, can lead to a spike in the stress hormone cortisol, which counteracts melatonin.

And not only are the results of the study limited by the number of participants who took part – you’d want more to confirm whether the results are truly accurate – but it’s clear that there are still benefits to reducing the amount of light you’re exposed to in the hours leading up to bedtime.

As the study’s authors told Medical News Today, the short-wavelength light that our ganglion cells are most affected by can still be produced by the screens of our phones and tablets, even when it doesn’t appear to be blue. That’s why the team still recommends people reduce their exposure to this kind of light before bed, dimming screens and overhead lights where possible to avoid disruption. 

Images: Getty