I'm not sure if a tablet with it's backlit screen gives off more of a glow than an e-reader with a lighted cover? If you decide to get an e-reader, I doubt there is really any particular one that is better than any other in this respect. The 'official' lighted covers look pretty good (I particularly like the latest Kindle ones), but they are expensive (about $50). Or you could just buy a clip-on light. Anway, a couple of links that show what these covers are like:
Kindle Touch lighted cover
Sony PRS-T1 lighted cover