It seems that Apple will release their own implementation of f.flux as part of iOS 9.3. All I can say is finally! I have been using f.flux on my Macs for ages and looking at the iPhone after having used the Mac screen during the evening feels terrible.
Many studies have shown that exposure to bright blue light in the evening can affect your circadian rhythms and make it harder to fall asleep. Night Shift uses your iOS device’s clock and geolocation to determine when it’s sunset in your location. Then it automatically shifts the colors in your display to the warmer end of the spectrum, making it easier on your eyes. In the morning, it returns the display to its regular settings. Pleasant dreams.
Source: iOS 9.3 Preview