One of the strengths of the iPhone display is its brightness. This is great during the day, when you want to be able to see the screen as easily as possible. Night time is a different story. We've all seen smartphone users' faces illuminated in a bright, blue glow at night. Not only does it look strange, but this light can actually interfere with the body falling asleep.
The developers of f.lux have a different idea, iPhone display lighting colors that actually match the time of day. They have released similar software for desktop computers, which automatically adjusts the color of your display. F.lux is smart enough to know when sunset occurs based on your location, so your iPhone adjusts without intervention.