I was thinking of buying a glowy reader, but after reading about the NST Glowlight problems and realizing I like my rooted NST much better than a Kindle, I decided to buy a light instead. After researching a bit I settles on the Kandle II. It illuminates the whole screen of my NST. The side opposite the Kandle (usually the bottom) is just a touch darker, but I don't suppose it would be much worse than the screen irregularities I've heard about on lighted readers. The Kandle II weighs about an ounce and doesn't require any real adjustment to light the whole screen.
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There's also the Kandle Flex, which looks interesting. The Kandle "I" had a bunch of problems (lots of the negative reviews on Kandle II are actually issues from the first) so I'd steer clear of that one.