Ashrem I cannot agree with the 'negative effect' issue. Just like the + or - zoom control, a simple script to vary the gamma level (brightness) a range of, say, 10 steps would give all/any user an easy variable effect from current (daylight) to apparent dusk lighting or even darker if desired. And only those wanting to use it are going to use it anyway. Which from what I've heard, would be about 1/4 of the people I've asked about it. That much participation would make that a worthy inclusion. In my humble opinion, anyway.
It sure wouldn't take a dev long to try it and see.