Using 12.04 on an Acer Aspire V5-561-9410. When I use the function keys to modify screen brightness (or use any solutions I've found here to this problem like the one found here or here), I see the brightness bar appear and change in the top right of my screen, but my actual screen brightness doesn't change. Does anyone know of a fix for this? I'm assuming it's a related issue, but I also don't see any change in screen brightness when going from running on AC power to running on battery.
This may not be the most modest approach, but it works for my Ubuntu 12.04 Acer.
You will need to run this command as super user (su).
$ sudo su # echo 200 > /sys/class/backlight/intel_backlight/brightness
This will change your brightness (on a scale of 0-1000). Be careful you don't put in 0 or your screen will turn off!
If this process works for your machine, it's not too difficult to write a short script that macros the command to your keyboards shortcut keys.