So, sometimes you need to work at night and not light up the whole room (e.g. when there is a sleeping baby next to you). The dimmest setting on the mac screen is still annoyingly bright, and indeed after a while, begins to hurt my eyes. One native thing to try is "invert colors" under "screen" in "accessibility". It makes the screen look like a negative image. It looks very cool, a bit annoying if you have images, but for text it is a very good counterpart to bright backgrounds during the day.