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Using ‘night mode’ on a smartphone might not improve your sleep after all

New findings from Brigham Young University suggest that blue light by itself isn’t what’s causing people to lose shut-eye.

Using ‘night mode’ on a smartphone might not improve your sleep after all
[Photo: Ketut Subiyanto/Pexels]
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The tech industry is under the impression that the blue light from screens disrupts our sleep cycles. See: Night Shift, the five-year-old Apple function that adjusts screen colors to warmer hues in the evening, and various Dark or Night modes on Androids.

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One problem: A new study finds that Night Shift has no impact on sleep.

Researchers at Brigham Young University asked 167 adults, ages 18-24, to stay in bed for at least eight hours per night after evening use of either their smartphone with Night Shift, their smartphone without Night Shift, or no phone use at all. “There were no differences across the three groups,” says coauthor Chad Jensen, an associate professor of psychology at Brigham Young University. “Night Shift is not superior to using your phone without Night Shift, or even using no phone at all.”

The researchers used wrist accelerometers to measure sleep duration, sleep quality, awakenings and time to fall asleep. Their finding suggests that blue light by itself is not impacting sleep.

This is contrary to a number of small studies that have found that evening screen use impacts melatonin levels, cognitive performance and alertness, and sleep quality. However, these were all very small studies that took place in lab conditions—for example, asking participants to read an e-book for four hours in a dim room—and none confirm that blue light itself is the culprit. The new study followed participants in their typical home lives, tracking how they actually interact with their phones. Further research is necessary.

One useful side tidbit emerged here: Among people who were generally well-rested (6.8 hours of sleep per night or more), those who didn’t use phones at all before bedtime enjoyed better sleep quality than those who did. But there was no difference among people in sleep deficit (under 6 hours of sleep per night). “This suggests that when you are super tired, you fall asleep no matter what you did just before bed,” says Jensen. “The sleep pressure is so high there is really no effect of what happens before bedtime.” In other words, when you’re tired, do whatever you want right before bed. 

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Overall, this suggests that what keeps some people awake may not be blue light, but simply the cognitive and psychological stimulation of using a phone—aka, the alertness that comes from the engagement of texting, scrolling, and posting. Keep your eye out for further study on the topic.