There's actually a difference there, though: books aren't a light source. When you're reading a book, you're reading it with indirect/reflected lighting. This really does make a difference with respect to eye fatigue. And, for that matter, think about the difference between reading in your living room with nice ambient lighting and trying to read the same book in bright sunshine in midday. The "white level" is much higher in sunshine but the black level remains about the same -- in other words, there's much higher contrast -- and it's harder to read.
It's certainly possible to go overboard with low contrast on web pages, but most of the research I've read suggests that there's a happy medium. What you want to aim for, IIRC, is around a 50-70 point difference in lightness on the LAB color scale between the main background and main body text, at least if you expect to be throwing article-length text at people rather than Twitter-length text.
It's certainly possible to go overboard with low contrast on web pages, but most of the research I've read suggests that there's a happy medium. What you want to aim for, IIRC, is around a 50-70 point difference in lightness on the LAB color scale between the main background and main body text, at least if you expect to be throwing article-length text at people rather than Twitter-length text.