I created this script to edit screen brightnes on a macbook.
First you have to install applesmc-dkms:

first add this line:
to your apt sources.list
Code:
nano /etc/apt/sources.list
then install it
Code:
apt-get install applesmc-dkms
now use my script
Code:
#!/bin/bash

# Francesco La Placa (frank10gm@gmail.com)
#
# This program just modifies the value of backlight for Apple Laptops
# You must run it as root user or via sudo.
# As a shortcut you could allow to admin users to run via sudo without password
# prompt. To do this you must add sudoers file the next contents:
#
#  Cmnd_Alias CMDS = /usr/local/bin/backlight
#  %admin ALL = (ALL) NOPASSWD: CMDS
#
# After this you can use this script as follows:
#
#     Increase backlight keyboard:
#	    $ sudo backlight up
#     Decrease backlight keyboard:
#	    $ sudo backlight down
#     Increase to total value backlight keyboard:
#	    $ sudo backlight total
#     Turn off backlight keyboard:
#	    $ sudo backlight off
#

BACKLIGHT=$(cat /sys/devices/virtual/backlight/apple_backlight/brightness)
MAX=$(cat /sys/devices/virtual/backlight/apple_backlight/max_brightness)
INCREMENT=1
MIN=0

if [ $UID -ne 0 ]; then
    echo "Please run this program as superuser"
    exit 1
fi

case $1 in

    up)
        TOTAL=`expr $BACKLIGHT + $INCREMENT`
        if [ $TOTAL -eq $MAX ]; then
		echo $TOTAL > /sys/devices/virtual/backlight/apple_backlight/brightness
           	exit 1
        fi
        if [ $TOTAL -gt $MAX ]; then
            let TOTAL=MAX
        fi
        echo $TOTAL > /sys/devices/virtual/backlight/apple_backlight/brightness
        ;;
    down)
        TOTAL=`expr $BACKLIGHT - $INCREMENT`
        if [ $TOTAL -eq $MIN ]; then
		echo $TOTAL > /sys/devices/virtual/backlight/apple_backlight/brightness
             	exit 1
        fi
        if [ $TOTAL -lt $MIN ]; then
             let TOTAL=MIN
        fi
        echo $TOTAL > /sys/devices/virtual/backlight/apple_backlight/brightness
        ;;
    total)
	TEMP_VALUE=$BACKLIGHT
	while [ $TEMP_VALUE -lt $MAX ]; do
		TEMP_VALUE=`expr $TEMP_VALUE + $INCREMENT`
		if [ $TEMP_VALUE -gt $MAX ]; then 
			TEMP_VALUE=$MAX; 
		fi
		echo $TEMP_VALUE > /sys/devices/virtual/backlight/apple_backlight/brightness
	done
        ;;
    off)
	TEMP_VALUE=$BACKLIGHT
	while [ $TEMP_VALUE -gt "0" ]; do
		TEMP_VALUE=`expr $TEMP_VALUE - 1`
		if [ $TEMP_VALUE -lt "0" ]; then TEMP_VALUE=0; fi
		echo $TEMP_VALUE > /sys/devices/virtual/backlight/apple_backlight/brightness
	done
	;;
    *)
        echo "Usage: backlight up|down|total|off"
        ;;
esac
If you want, assign the script to functions keys in system->preferences->keyboard shortcuts (ex: "/script_folder/backlight up" to F5)