Comment 54 for bug 954661

I can confirm this regression in 3.8.0-22. Only noticed it when I went on battery today.

Fix for me was the same as beerfan above. I also went one step further and added:

echo 0 > /sys/class/backlight/intel_backlight/brightness

to rc.local and the following:

#!/bin/sh
# to fix backlight issues on resume

case "${1}" in
resume)
echo 0 > /sys/class/backlight/intel_backlight/brightness
;;
esac

to /etc/pm/sleep.d/99-backlightfix (remember to make it executable!). Might need to alter it a bit to make it work for hibernate but brightness control works on resume. Will test again on the next kernel update.