When iOS 9.3 was launched back in 2016, one of the most talked-about announcements was Night Shift, a feature that adjusts the colour output of the screen at night in order - in theory - to improve sleep. But does it actually work?

MacRumors reports that psychology professor Chad Jensen at Brigham Young University in Nevada has tested the feature's effectiveness. He examined the sleep of 167 people between 18 and 24 years old, comparing those who used a smartphone before bed with ‌Night Shift‌ turned on, those who used a phone without ‌Night Shift‌, and those who didn't use a phone before bed at all.

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

Jensen also compared the effects of the feature on a variety of sleep patterns. In the group with individuals who slept less than six hours per night - those who might be considered most in need of assistance - Night Shift had no observable effect at all. In the group that averaged about seven hours of sleep per night, Night Shift provided only a marginal improvement in sleep quality; bigger improvements were gained by those who didn't use a phone at all.

Chad Jensen's conclusion is that too much focus is currently placed on the technical issue of blue light produced by screens, which is what features like Night Shift are designed to minimise. In fact, he argues, it is simply the use of mobile phones that disturbs our sleeping habits the most, and for optimal bedtime conditions we should put away our electronic devices well before sleep time.

Although Night Shift may not help us sleep better, it may be helpful for our eyes... but that's a different story.

Night Shift should not be confused with Apple's True Tone screen tech, which also adjusts colour output but in different ways and for different reasons. Read True Tone vs Night Shift for an in-depth explanation.

This article originally appeared on Macworld Sweden. Translation by David Price.