Ubuntu 14.04 - brightness problem in HP hybrid laptop
Solution 1:
sudo gedit /etc/default/grub
find this line:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
and change it to:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"
and then: sudo update-grub
That works for my HP ProBook. Here is where i found the solution: http://www.techjail.net/solved-brightness-problem-in-ubuntu-12-04-precise-pangolin.html