EDIT: Updating to Ubuntu 13.10 solved this issue for me out of the box.

I'm trying to get some control over the brightness of my Samsung QX411 (Integrated Intel and discrete Nvidia, though Ubuntu doesn't see the latter yet, I'll play around with Bumblebee later)

Using the FN+up/down lowers the screen brightness from max to one peg down or back up. If I try to bring the brightness down any more, it just flickers and stays the same.

I can lower the brightness in Settings, but that's delicate and gets reverted to max if I open up the brightness settings again, or log out.

The closest I got was adding acpi_backlight=vendor to a line in /etc/default/grub, (source) I could consequently lower the brightness a couple of pegs down to the minimum with FN+down, but then it's as if the problem got inversed, and I'd get stuck in the bottom tier, I could only increase the brightness by one peg and back down. Rebooting would revert to max brightness.

acpi_osi=, acpi_osi=Linux, acpi_osi=vendor, acpi_osi='!Windows 2012', acpi_backlight=Linux, acpi_backlight='!Windows 2012' don't do anything for me.

I've also tried adding echo 2000 > /sys/class/backlight/intel_backlight/brightness to /etc/rc.local, where my max value from cat /sys/class/backlight/intel_backlight/brightness
is 4648, which didn't do anything.
(same result with echo 2000 > /sys/class/backlight/acpi_video0/brightness)
source

Samsung tools also didn't help in this regard.

I've spent hours on this, it's getting quite frustrating. Any help would be greatly appreciated.