About flicker: wrong. Lcds do flicker, crts were more noticeable because they are interlaced displays that change their screen at 30 Hz since they have to use up half of their refresh rate changing the interlacing (and there is a slow decay inherit to the technology, plasmas also have this decay that is what makes plasmas look more crt like than lcds). Lcds refresh the screen at 60 Hz minimum. It still flickers just so fast that we can't see it.
About eye strain: this doesn't require physics. When the screen is brighter than the surrounding environment it is easier to get eye strain because it is harder to focus on something else in the room from time to time. That is why I use a backlight when I watch tv, and I use autodim on my iphone. A kindle reflects the light, and is thus always the same intensity as the rest of the room... so it is harder to get eyestrain reading on it.