Checking social media, news updates or group WhatsApp messages before bed has long been blamed for a night of tossing and turning.
Rather than counting sheep, smartphone users may turn the device to night mode, a feature introduced by Apple and Android, supposedly to help people fall asleep.
With any claims of the features' benefits purely anecdotal, scientists from Brigham Young University (BYU) analysed the sleep outcomes of 167 young adults.
For an hour before bed across seven consecutive nights, the participants either used an iPhone with its Night Shift mode enabled, the same device with Night Shift disabled, or no phone at all.
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Results reveal there was "no significant difference in sleep outcomes" across the three groups.
The blue light emitted from phones, laptops and tablets was once blamed for users struggling to fall asleep.
Rather than pointing the finger at blue light specifically, the general glare given out by these devices is now thought to suppress the release of the sleep hormone melatonin.
To help combat this, Apple introduced the iOS feature Night Shift in 2016, which "uses the clock and geolocation of your device to determine when it's sunset in your location".
"Then it automatically shifts the colours of your display to warmer colours," according to Apple.
Android soon followed suit, with most smartphones now having a similar feature.
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To better understand Night Shift's effects, the BYU scientists looked at 167 adults aged 18 to 24 who typically used a mobile phone every day.
After being divided into the three groups, the participants attempted to sleep for at least eight hours, while wearing a wrist accelerometer to record the quality and duration of their shut eye.
"In the whole sample, there were no differences across the three groups," said study author Professor Chad Jensen.
"Night Shift is not superior to using your phone without Night Shift, or even using no phone at all."
In a second half of the experiment – published in the journal Sleep Health – the scientists separated the participants into those who got around seven hours of sleep a night and those who got by on less than six hours.
The team found the participants who got seven hours of shut eye – the lower end of healthy recommendations – had a slightly better quality of sleep if they did not use an iPhone before bed, regardless of whether it was on Night Shift.
"This suggests when you are super-tired, you fall asleep no matter what you did just before bed," said Professor Jensen.
"The sleep pressure is so high, there is really no effect of what happens before bedtime."
Rather than just a phone's light exposure keeping people awake, the mental stimulation that comes from scrolling may also discourage sleep.
"While there is a lot of evidence suggesting light increases alertness and makes it more difficult to fall asleep, it is important to think about what portion of that stimulation is light emission versus other cognitive and psychological stimulations," said Professor Jensen.
Yahoo UK has approached Apple for a comment.
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