Is Using Your Phone Before Bed Actually Disrupting Your Sleep?

Pre-sleep exposure to blue light produced by smartphones or laptop screens seems to not interfere with sleep quality as much as previous research led us to believe.

It’s a popular misconception that using modern technology right before bed can affect the length or quality of your sleep. Conventional wisdom made us believe we should turn off all screens before going to bed. It is thought that using digital media of any kind might interfere with our natural sleep cycles. But in the twenty-first century, where electronics are so commonplace, it is unlikely that many of us are avoiding screen time for an hour before bed.

Many studies over the past decade have linked poor sleep to using digital screen devices before bed. They discovered that pre-sleep exposure to blue light produced by smartphones and laptop screens could interfere with sleep quality and make people less sleepy. One of the supposed explanations for this is that the melatonin hormone, which usually tells our body that it is time to go to bed, is blocked by biological systems due to blue light exposure.

The earlier studies have limitations

Most of the research treated using a device as a single, homogeneous activity. They often ignore the subtle and complicated range of ways we use digital media. Most of the studies on the topic rely on self-reported sleep diaries, which are infamously unreliable.

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Is Using Your Phone Before Bed Actually Disrupting Your Sleep? 4

This study dwelled deeper

The study showed that if you are only exposed to a modest amount of the blue light that smartphones and laptop screens emit, it may actually not harm how well you sleep. 

Christine Blume and her colleagues at the University of Basel in Switzerland decided to investigate further to see if blue light, which exclusively affects the eyes’ intrinsically photosensitive retinal ganglion cells (ipRGCs), could have any impact on the quality of the subsequent sleep.

IpRGC PLR by William Thomas Keenan under CC0 1.0

“Light activates the eye cells, including rods and cones. However, intrinsically photosensitive retinal ganglion cells are particularly sensitive to blue light and are believed to play a significant role in determining the body’s internal circadian rhythms,” says Blume.


What did the researchers do?

Under laboratory conditions, the researchers studied 29 people by exposing them to two different types of light. All the participants were an average age of 23 and had healthy sleep histories.

The participants were exposed to one type of screen light for an hour on one of the nights they were in the lab. The exposure was terminated 50 minutes before their usual bedtime. The participants went to bed on average at 11:00 PM. They experienced a night with a different lighting scenario around a week later.

To the participants, the two distinct lights would have appeared nearly identical. But one had a large proportion of blue light, which the specialized retinal ganglion cells would be able to detect. The other light had a far lower blue light percentage, which would not be detected by these cells. An electroencephalogram (EEG) gadget monitored brain activity while the participants slept.


They also measure changes in melatonin levels

The researchers collected saliva samples from the volunteers every 30 minutes in the five hours before they went to bed to monitor changes in melatonin levels. 

Samples were also taken in the morning. Before going to bed, the participants were asked how tired they felt. And in the morning, they were questioned about how well they slept and how alert they felt.

What Blume and her colleagues discovered

Compared to other light frequencies, the blue light that was meant to affect melatonin lowered the hormone levels in the blood by an average of 14 percent. But there was no impact on self-reported sleep quality.

Melatonin In The Brain
Melatonin In The Brain by KathyG123 under CC BY-SA 4.0

According to Blume, melatonin and sleep are probably not as tightly related as people believe. She explained many reasons are behind why blue light may not have had an impact on the participants’ sleep.

Two factors mostly determine when you need to go to bed:

• The pressure to sleep builds during the day; and


• The circadian clock, which is the body’s internal clock that regulates when we need to go to bed and wake up on a 24-hour cycle.

The interplay of these factors also has an effect. According to Blume, sleep pressure may outweigh blue light effects on the circadian clock in young people (like those who took part in the study) without any obvious health issues.

The blue light effect can be driven by other eye cells

The study also implies that other eye cells rather than ipRGCs may be responsible for the blue light effect on sleep quality.


Blume emphasized if they had kept the screens on closer to bedtime, it might have taken the participants longer to fall asleep. However, the researchers needed to question the participants and let them brush their teeth.

It’s complicated and there is no simple answer

Although some studies have found that using a device before bed may not be bad for sleep, lots of current research has suggested the opposite. It is evident that science is having a difficult time coming to a consensus on this complicated problem.

According to Blume, the current study demonstrates that brief nighttime exposure to bright light does not always affect sleep. “I don’t believe this study alters how we generally see blue light’s effect on sleep. Rather, I believe it only adds to the body of existing evidence,” she adds.


Stuart Peirson from the University of Oxford explained that “this does not demonstrate that exposure to blue light before bed will not impair sleep. It only demonstrates that the study’s use of the particular type and intensity of blue light was unsuccessful.”

According to Hugh Selsick from University College London, “I think what this work alludes to is how intricate the processes of sleep and awake may be.”

“The role of melatonin in sleep-wake regulation is well established. But it is only one of many factors involved in the process, such as the mental state, homeostatic sleep drive, physical health, and environment, among many others,” he adds.


Featured image credit: Shutterstock

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