I found this old bug report about user-customizable minimum brightness setting, that says "Fixed in Fremantle", but I still don't know how to customize the brightness level: https://bugs.maemo.org/show_bug.cgi?id=1261 Anyway I think the levels are not hardcoded but computed from the brightness levels and brightness_max, if you look at 255/5 it's 51, which is exactly what the levels are multiples of...