Some addition things worth considering
Effective intensity of observed object (last I checked, paper isn't a mirror and doesn't reflect very well)
Frequency profile of the light being observed (cf light from the sun being imperfectly reflected vs lamp being reflected vs direct light source)
Ambient light around observed object which affects both stimulation profile of receptor region of eye AND pupil dilation
So yeah original emitter source isn't the only piece of this puzzle
Whether you're looking "at the lamp" or at a newspaper that reflects light, the end result is the same: photons hit your eyes.
No, I don't buy the green screen argument, any more than the randomness of paper being somewhat white and ink being in contrast to that. Certainly white on black is useful in astronomy, the stuff you are interested in is lit. This article was such a wall of text, I don't know if it ever supported its conclusion very well, which is ironic for an article promoting "productivity".
Not sure what this even means, sarcasm or not.
If the sun could be set in "low brightness", like a screen can (and ignoring infrared), then yes, you _could_ stare in the sun.
Screens should not be brighter than ambient light as a rule of thumb, i.e. if you hold a piece of paper next to your screen, the screen should not brighten up the paper. If it does, reduce brightness of your screen and/or turn up the light in your room.
So, a dark room is not an ideal working environment anyway.
I think it makes all the difference in the world.
Aside from power consumption, e-books and e-paper displays exist for this reason.