I keep my mac on when I go to bed...and the light it makes is terrible for trying to fall asleep...so i found this neat tip that doesn't require any downloading of any kind! Simply use control+shift+eject and your screen instantly darkens!
I knew about this as it was a workaround to the striped backlighting issue on some MBPs. However, mine doesn't stay off. After I hit ctrl-shift-eject and release eject, it's dark, but when I release ctrl or shift my screen turns back on.
You can also set a hot corner to sleep the screen. You can even set a modifier key so you don't accidentally sleep the screen when you don't want to. I use cmd + bottom left corner.
This trick actually puts the computer to sleep- not the display alone.
or you can just turn the darned thing off for the night!![]()