Exposure to light late in the day or in the middle of the night will phase delay the body's clock, making one want to wake up later and go to sleep later.

“So the simple way to think about this is if you're having trouble waking up early and feeling alert early in the day, you're going to want to try and get bright light exposure even before waking up because it will advance your clock. It's sort of like turning the clock forward. Whereas if you are having trouble waking up early, you definitely don't want to get too much light exposure or any light exposure to your eyes late in the evening and in the middle of the night because it's just going to delay your clock more and more.”