[tomsem]

The screen contrast is identical (they both use the same screen, with the same physical properties).

Proof: take a screen capture from your Kindle and make it a custom screensaver image on Nook. Compare side by side. They are the same.

So to the extent that there's a difference in contrast, it has to do with fonts.

Amazon has beefed up the smaller text sizes. They more resemble Caecilia/Helv Neue demi-bold (the weight between normal and bold) than 'normal'.

To illustrate this, I created a 'font test' epub file that uses embedded fonts, with samples of each font in the Caecilia and Helvetica Neue family (well. I messed up on Caecilia Heavy, it is actually Bold.). Now, if you compare the two devices, with larger sizes in the same typeface, to my eye at least, they're indistinguishable. It's only the smaller sizes where Nook looks 'lighter'. And one could even argue that by 'artificially' increasing the weight of the smaller sizes, Kindle is not accurately rendering the letterforms as designed, while Nook is. (But functionally, I agree, Kindle is 'better')

That said, I think Nook would do well to have a 'saturation' adjustment like Sony. This would shift the grey anti-aliased pixels to the blacker ranges and would make the smaller text sizes more readable (Kindle has a similar feature but it only applies to the PDF viewer). Since Nook potentially can display virtually any font (via font embedding), it could help improve the reading experience when a font with relatively narrow strokes is used (any strokes less than a few pixels wide start to fade out due to anti-aliasing).

To get a flavor of this, bring up the Text options panel, select the smallest text size, then dismiss it. The text that is redrawn under the panel looks noticeably darker (at least on my Nook), though it is a little subtle perhaps.

The more I read on my Nook, the less I am bothered by light text, and I would prioritize fixing several other things over doing anything about this. And though Kindle's text looks darker in smaller sizes, its typography (lacking hyphenation even of hard coded hyphens and em dashes) is not nearly as good, often leaving poorly justified text and rivers of white space (compounded because the default margins are too wide—fortunately there's a very easy hack to correct this). So overall I prefer Nook's text rendering to Kindle's.