A recent study by Harvard researchers find that E Ink displays with front lighting are up to three times less stressful for retinal cells than LCD displays. E Ink displays without a front light do not emit any blue light and so are not stressing retinal cells at all.
Blue light, according to researchers, is potentially harmful when emitted into the eyes for hours at a time. Blue light poses a hazard to retinal cells in the eye, and exposure to blue light near bedtime reduces levels of the sleep-inducing hormone melatonin, disrupting the circadian rhythm and restorative sleep.
The effects of blue light are known for a long time, and this new research finding is not surprising.