[sbierwagen]

A rule of thumb I've heard is that your monitor shouldn't be any brighter than a sheet of white paper held next to it.

http://i.imgur.com/5Cwiuif.jpg

Mine isn't quite that dim, but it's not nearly as bright as the view out the window behind it.

[marcosdumay]

It certainly should not be the brightest thing within your sight.

[Grangar]

Wow, good one! I tried that and turned out my monitor was set really high. Let's hope this will be easier on my eyes.

[jotato]

I keep mine set to what seems like the brightness of everything around it. On this montior, that is 20/100