This is an excellent free resource for the chronologically challenged late night student or web surfer:  http://www.stereopsis.com/flux/
It is a small program that you download and install. It takes just a couple minutes to setup, then you forget about it.  Throughout the day, f.lux will subtly and gradually alter the color temperature of your monitor. You don’t really notice it, but as the night progresses you tend to be more sleepy than you would if you were web surfing or working without f.lux. So it is
easier to maintain a sleep schedule.