From an article in TechCrunch:
Back in November, I speculated that the new Kindles and Nooks and what have yous might have glowing screens, the likes of which we’ve seen occasionally but were never fully implemented. It turns out Amazon was thinking the same thing, and actually bought a company that was, I am told, the world leader in light-guide technology. They’ve finally gotten it to the point where it’s ready to be released, and a new generation of glowing Kindles will be coming our way sometime this year.
The device I saw was crudely camouflaged in a sort of cardboard enclosure, but the screen was clearly visible. With a tap, a slider popped up on the screen, and as it was dragged to the right, the screen lit up evenly with a rather cool light. In the dark, it was plainly noticeable as a glow, and in uneven light — say, shade or a shuttered room — the slight illumination made the screen much more readable. At full blast it was definitely projecting some light (technically speaking it was reflecting it), but it was still a soft glow and not the harsh flashlight of a backlit LCD.”
More details in the article.