Contraversy to what most people think, the real danger of LCD is the backlight lamp. Imagine flash light pointed to your eyes... it's exactly how LCD works. As I allready pointed somewhere, I had the problem with the eyes (low vision in evening and dark) and that were caused by LCD. Before LCD i used CRT (the real good one with 120hz refresh rate) 5 years\10 hours on computer daily and no any problem with vision.
The second problem with LCD backlight is *LAMP FLICKING*, contravercy to CRT (where we had image flicking), LCD image has no distructive flicking, but LAMP flicking around 60HZ and thats also bad for eyes. This problem were solved about 2 years ago, but there's still some LCD displays which used old lamp.
So pixelqi without backlight is safe enough for your eyes.
On other hand e-ink still have contrast problem. Contrast ratio on current e-ink (and especially on EE) is not safe for using by children, and if you an adult, than it's recommend to read in good light envoverment to save your vision.