One of the earlier Sony's also used a layer to create lighting. I think it was the PRS-700(?). It was a big failure as it definitely made the text harder to read. They also introduced a special light cover that used a flip down layer of clear plastic that created the light similar to how the 700 did. I had one for my 600 I believe and it to was terrible. I never saw the 700, but the 600 with lighted clear plastic cover was a headache inducer. But this was a few years ago and it looks like Amazon has done it without these side effects.

BTW, both the 600 and 700 used the older, lesser contrast pre-Pearl eInk screens.