The thing is, unless you're in a blackout room like a theater, there will be other sources of light already reaching the reading surface. In order to overpower

The thing is, unless you're in a blackout room like a theater, there will be other sources of light already reaching the reading surface. In order to overpower the existing light enough that the contrast ratio between text and background is strain-free, you'd often need to crank up the intensity of one or the other to the point that it starts to become as uncomfortable as looking at a traditional display.