bobcathy has the best idea. prefer natural light, then incandescent, then halogen (dimmable, preferably. this is the one advantage of halogen lamps: most are dimmable), then fluorescent. never right over the screen, or reflecting off the screen.
i'll presume you meant fluorescent in the first paragraph. you may have thought that the lights in the office were good, because you could always see the screen, but most likely they making your office way too bright. the monitor itself is a source of light, and fluorescents just overload your eyes. with a more gentle source of light i'll guarentee you'll feel better at the end of the day.
complex