I find it harder to fall asleep when I've been up late watching TV or sitting in front of any similar electrical device that fires a stream of electricity through a phosphorous gas mix at 70kHz into my face(i.e., a computer monitor).
We human creatures are finely attuned to variations in light, and it's natural for us to sleep after a period of darkness, so when we give ourselves high doses of light at night it's just like sending a signal to the brain saying "there's still light out there, you need to stay awake more!"

Yet here I am sitting in front of my electron beam at 4am.
:(