Well more like... Can a computer screen cause headaches when there is no major light source in the room? (FYI: The room's lights are off and blinds on the window is closed). I'm kinda curious here.

Of course. I usually just take paracetamol. Heh.

Yes. Televisions do this too. It's why there are http://www.tvlamps.net/. I recommend having a desk lamp on during the night hours to prevent eye straining (which leads to migraines).

Yes. Always a good idea to have some dim light in the room so it's not completely dark.

It varies from monitor to monitor too, my old fat 17" Hanzol CRT from 1999 was extremely unpleasant and actually managed to even make my eyes cry on several occasions because it made them sting, while my current http://www.eizo.com/global/products/flexscan/ev2336w/ is extremely plesant and automatically adjust the brightness of the monitor depending of the light in the room.

This is also why http://www.youtube.com/watch?v=hE8K0kwmv0Y are nice, not only do they bright up the room a bit, but they light up the wall behind the TV differently depending on what's on the screen.

Okay. That explains my headaches the past week... I've been listening to my step mother and having my light off during the daytime which caused the room to be "dark" (not pitch-black dark, mind you)... Cause, you know, apparently having lights on in the room is wasting electricity cause the sun should provide enough light for the room (but it really doesn't due to trees and such in the way. Plus I hate having my blinds open because I don't trust people looking into my room... Paranoid, I know).

Yep, any kind of eye strain can cause headaches.

http://www.pcworld.com/article/258703/how_to_eliminate_eyestrain_from_your_big_beautiful_pc.html

I have those bias lighting LED strips on the backs of my monitors, and they seem to help as long as the monitors aren't too far away from a wall to reflect the light. They do seem to improve the perceived contrast of the monitors when the room is dark, too...a little.