Comment 6 for bug 140782

@Matthew Garrett:

The problem is that, when brightness max levels is more than 20, g-p-m use an increase/decrease step value of max_levels/20 (5%).
So, in my case, acpi reports brigthness max levels=100, and possible brightness values are: 12 24 36 48 60 72 84 100.

When I'm at 72, if I try to increase brightness using hotkeys, g-p-m tries to set brightness to 79, but it's not enough to get to the next brightness level. Please also read my comment at <https://bugs.launchpad.net/ubuntu/+source/gnome-power-manager/+bug/140839/comments/5>.

This has been also reported at bug #140839.