iOS 9.3 Beta, released today, adds a neat feature to iOS 9, called “Night Shift”. Night Shift is designed to reduce the amount of blue light an iOS device is putting out during the evening hours. Blue light can negatively impact sleep by altering the body’s circadian rhythm.
When Night Shift mode is enabled, your device will determine when sunset is at your location and the iPhone’s screen will automatically change towards the warmer (yellower) colors in the spectrum, reducing blue light at that time. In the morning, the display automatically turns to its normal temperature color, mimicking natural daylight.