night mode with reverse video?
I have found under setting (in Android 4.3 anyway) that I can go to Device: Accessibility:Negative Colors.  This will produce the "inverse video" effect so normally white backgrounds are black.  In conjunction with normal (or app enhanced) screen dimming this reduces liht significantly over the normal black on white output.

I will update this answer if I find a way to control backlight brightness.

Update: This mechanism does not work when the onscreen keyboard is involved, as those are typically dark and negative video makes them too bright.