i have ubuntu 12.04 and sony laptop, and i've installed nvidia driver. screen brightness changing (with keyboard fn keys) and keyboard backlight works in unity, but it doesn't in kde. when i issue the command:
echo 8 > /sys/class/backlight/acpi_video0/brightness
it changes brightness, but it doesn't anything when i press brightness functions keys, even displaying a bar.
and also when i enter:
echo 1 > /sys/devices/platform/sony-laptop/kbd_backlight
it turns on keyboard backlight but it is not turned on by default. the best practice is what happens in windows: turn it on when you're in a dark place, using a light sensor.
thanx for your help ;)