Debian - slow brightness responce on Dell laptop fix

On some Dell laptops with gnome3 brightness change takes veeeery long (seconds) and system is choppy in the meantime.

A workaround has been posted on https://bugs.launchpad.net/ubuntu/+source/linux/+bug/828296/comments/5 and is to:

1. add acpi_backlight=vendor to GRUB_CMDLINE_LINUX_DEFAULT option in /etc/default/grub file (eg. GRUB_CMDLINE_LINUX_DEFAULT="quiet acpi_backlight=vendor")
2. run $ sudo update-grub

Bug for ubuntu is filed: https://bugs.launchpad.net/ubuntu/+source/gnome-power-manager/+bug/847001

Worked on my Dell e6430.