Night Shift, a major new feature iOS 9.3, is a display-based setting that lets you "warm up" an iPhone or iPad's screen at night to cut down on blue light exposure. Similar to f.lux on the Mac, Night Shift will automatically change the color temperature of an iOS device's display to reflect the time of day.
With Night Shift, an iPhone or iPad screen will look bright white with a blue-based lighting scheme during the day, but as the sun sets, that bright white will fade into a warm yellow that's easier on your eyes and your circadian rhythm.
What's the Deal With Blue Light?
Blue light, which is the light on the spectrum that makes our computer, tablet, and phone screens look so crisp and bright, is great during the day because it mimics a bright morning. Blue wavelengths wake us up, boost our attention, and let us know it's time to start the day.
At night, blue light is less desirable because that's the time when our bodies should be getting ready to wind down for sleep. Studies have shown that looking at a bright blue screen during the evening hours can confuse the body's biological clock and disrupt our natural circadian rhythm (the ~24-hour light and dark schedule everyone runs on) by suppressing melatonin production, making it harder to fall asleep. All light disrupts the circadian rhythm, but blue light has been proven to be the most disruptive.
On the Kelvin scale used to determine color temperature, an iPhone 6 display measures in at about 7100K, while an iPad Air 2 display is slightly warmer at 6900K. On the lighting spectrum, 6900K and 7100K blue light levels are similar to the light you would see on a bright, cloudy day outdoors. Blue light is also harder on the eyes, especially in an indoor room that's lit with a dimmer yellow light.
In a nutshell, your iPhone and iPad might be keeping you up at night, and Apple's solution to that problem is Night Shift.
Activating Night Shift
Night Shift mode works by shifting the iPhone or iPad's display from a blue tint to a much more yellow tint, either on demand, automatically at sunrise and sunset, or on a custom user-set schedule. Night Shift is turned on in the Settings app.
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Article Link: How to Use Night Shift Mode in iOS 9.3
