Comment 37 for bug 121833

I thought of a different way to re-add zero: simply allow it as one of the usable values. As it is right now, gnome-power-manager's indicated brightness levels
(100, 85, 71, 57, 42, 28, 14, 0)
 no longer match the indicated values in the dsdt:
(100, 87, 75, 62, 50, 37, 25, 12, and a true zero you could add.)

In addition, some time try out guidance-power-manager, and you'll notice that its backlight control is far more sane -- it actually remembers the levels you set for each power state.