I was thinking about how my eyes get fatigued after looking at a computer or TV screen for too long and it occurred to me that it takes much longer for them to fatigue when looking at a book. It seems to me that the difference is that a screen emits light whereas a page in a book only reflects light. I'm sure it's possible to create a display that is only reflective and does not emit its own light, thereby reducing eye fatigue. Do such displays exist? If so, why are they not in wide use? How do they work? If they don't exist, why not? Is the problem technical or is this just something that nobody wants?