Problem:

I'm trying to figure out how to modify my working conditions so that I can program longer without harming my eyes. Because doing so experimentally hasn't given conclusive results so far, I decided to ask for studies in this area.

Required:

Question: Does looking at a bright screen in a well lit room strain eyes more than looking at dark screen in a dark room for prolonged periods of time?

Question: Is there a middle ground somewhere in-between that is most harmless?

Question: Is it a combination of contrasting screen/background?

I'm not asking for medical advice here. I already went to several doctors and they gave me different, sometimes contradicting answers, so I'm just looking for research.

Any ideas? Or better yet, pointers to places where this has already been answered?