In general, looking at your phone at night is a terrible idea.
Smartphone screens emit bright blue light so you can see them even at the sunniest times of day.
But at night, your brain gets confused by that light, as it mimics the brightness of the sun. This causes the brain to stop producing melatonin, a hormone that gives your body the "time to sleep" cues. Because of this, smartphone light can disrupt your sleep cycle, making it harder to fall and stay asleep — and potentially causing serious health problems along the way.
If you are an iPhone user who can't use f.lux, you haven't been able to tone down the levels of blue light coming out of your phone. Now, the recent iOS 9.3 update changes that. It enables a new mode called Night Shift that you can set starting at whatever you choose time in the evening. When Night Shift kicks in, your phone automatically adjusts the display so that it gives off warmer, less blue light.
Here's how blue light at night affects your brain: