I nurse and e-Read, and while I used to use my iPhone for 2-4 hours reading sessions, it made my eyes very cranky (even with low brightness and reversed text).
I have found the best combo to be an e-Ink device with a directed clamp-on light. The light I'm using right now is from Target:
http://www.simplyparticular.com/2010...ption-for.html
Because of the way this light is designed, if the little guy stirs, I just flip the light down and it blocks the light cast until he settles or I turn it off. I'm reading 3-4 hours with a nursing or sleeping baby AND my eyes aren't bloodshot.