With kindle, you need a very good light source. You know how the ads say you can read it in the sun? What they don't say is you practically NEED sunlight to read it
. The more light, the better it looks. I like to go outside, put on sunglasses, sit in the shade while positioning the kindle so sunlight falls right on it. In the evening, I use a bright white light on a flexible arm mount and position it so it points toward the kindle and away from my eyes. This gives the kindle 3 the maximum contrast and makes its background look paper like white.
Of course everyone's eyes are different so you need to figure out what works for you. But don't go cheap and buy a used kindle 2. Buy the kindle 3 with the better screen. If you find you need the font so big that you get too few lines on a page to read enjoyably, then return it and get the DX latest generation. You have 30 days and amazon service is excellent.