If your Acer Aspire V5 uses intel_backlight device instead of acpi_video0, then this set of scripts might provide a solution to you. See if you have intel_backlight device by examining the output of "ls -l /sys/class/backlight". To determine if your notebook responds to brightness commands on the intel_backlight device, start a root shell by executing "sudo -i" and then do this in the root shell:
Determine your maximum brightness:
Decrease brightness to a desired value, for example to half of the maximum brightness value (substitute 500 with your value):
echo 500 > /sys/class/backlight/intel_backlight/brightness
If your brightness has decreased, then use the above set of scripts to fix the problem with your brightness control hotkeys.
Finally, see how many steps you have for brightness control. If you completely decrease or increase brightness in about 5 key presses, then you should make one additional correction to your configs so that you have 10 steps to regulate brightness, as originally designed.
In your root shell, execute:
If you see 'Y' or '1', run the following command:
echo 'N' > /sys/module/video/parameters/brightness_switch_enabled
Replace 'N' with '0' if you received '1' as an output from the previous command. After that, you should have 10 steps for brightness control instead of 5.