your actually not supposed to read ebooks on a backlit screen. It causes strain to the eyes compared to reading an e-ink reader or an actual book.
Tell that to all the people happily using ibooks, kindle, or nook apps on their ipads today.
Or the zillions of office workers reading stuff on backlit screens for hours every day...
Sorry, that just doesn't hold water anymore.
Sure if you have it on 100% brightness and do black text on white background you'll cause a problem. That's why the readers have sepia tones and brightness adjustments, it reduces the contrast and more closely mimics the light bouncing off a paper or e-ink page.