Blue-light-blocking phone night modes don’t help sleep, study finds

Over the last few years some scientists have claimed the blue light emitted from the screens of many electronic devices can significantly disrupt our sleep patterns. To combat this almost every laptop or smartphone nowadays comes with a specific “night” setting designed to reduce blue light emissions. A new study testing these night modes is suggesting they make no difference to overall sleep outcomes and the only way to improve sleep at all is to completely abstain from screen use before going to bed.

A couple of decades ago scientists discovered that a light-sensitive retinal protein called melanopsin is produced by small retinal cells in the back of our eyes. Melanopsin is generated in response to light and it helps regulate our circadian rhythms, telling our brain to stay awake and alert.

Melanopsin has also been found to be especially sensitive to blue spectrums of light, sitting around wavelengths of 480 nanometers. This underpins many hypotheses suggesting LED screen and smartphone use in the hours before bed can disrupt sleep.

So in response to these ideas most smartphone makers have incorporated night modes designed to add a warmer hue to screens in the evening. On the iPhone this feature is called Night Shift, Pixel phones call it Night Light and Samsung simply has a Blue Light Filter setting.

But do these night modes actually lead to any measurable improvements in sleep outcomes? A team of researchers from Brigham Young University and the Cincinnati Children’s Hospital Medical Center set out to answer that very question.

The researchers recruited 167 young subjects and split them into three groups for a seven-night study. One group was required to spend an hour before bed using their iPhone with Night Shift mode switched on. A second group did the same but with the night mode turned off, while a third group was directed to not use a phone at all for the hour before going to bed.

Sleep quality was tracked using a wrist-worn accelerometer, and a variety of outcomes were calculated, including time to get to sleep, total sleep duration and frequency of waking during sleep. Chad Jensen, one of the researchers working on the project, says the results were pretty clear.

"In the whole sample, there were no differences across the three groups," says Jensen. "Night Shift is not superior to using your phone without Night Shift or even using no phone at all."

Digging into the data, the researchers divided the cohort into two groups – those averaging around seven hours sleep each night and those sleeping less than six hours a night. In the latter group, more chronically sleep-deprived cohort, again no differences in sleep outcomes were detected between all three groups.

"This suggests that when you are super tired you fall asleep no matter what you did just before bed," notes Jensen. "The sleep pressure is so high there is really no effect of what happens before bedtime."

In the cohort sleeping around seven hours a night the researchers detected some very minor improvements to sleep quality in those subjects not using a phone at all before bed. This compared to no differences whatsoever in both phone use groups.

Jensen says these results suggest blue light plays little to no relevant role in how quickly one falls asleep or in the quality of that sleep. Instead, he claims the psychological engagement of using a smartphone is a much more powerful factor in altering the quality of one’s sleep.

"While there is a lot of evidence suggesting that blue 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," says Jensen.

The new research is not the first to suggest popular blue light filters for LED screens may not be useful. A 2019 study from the University of Manchester found perceived colors of light may be vital in regulating human circadian systems. That study argued yellow spectrums of light used in night mode settings could be counter-productive, modulating melanopsin activity in ways that actually make a body think it is daytime.

There certainly isn’t enough evidence to suggest smartphone night mode settings are doing the opposite of what they intend, and there is good research showing how blue light wavelengths influence circadian-regulating mechanisms in the human brain. But this new study does offer some of the first empirical evidence to suggest your smartphone night mode may not be doing much to help you sleep, and ultimately, if you really want to improve sleep quality it is possibly best to simply not use a device at all in the lead up to bed time.

The new study was published in the journal Sleep Health.

Source: Brigham Young University