Hi Xiaopanda and welcome to MobiloeRead. I read on my iPaq for years and liked it fine but eInk technology is a great improvement. I especially like not having the back light shining in my eyes. My attitude has always been that you don't have back lighting with a printed book yet it's easy enough to read.
Anyway, there is a cover available for the Sony that has a built in light and seems to work fine. Check it out here
http://www.sonystyle.com/webapp/wcs/...52921665480080
Also, the 700 has the light built right into the reader.