I don't know if this can help but on my Dell XPS m1330 with Nvidia card, this is:
cat /proc/acpi/video/VID1/LCD/brightness which change. -- [hardy] [regression] LCD brightness control (Dell) no longer works https://bugs.launchpad.net/bugs/212733 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
