Brightness Controls Not Working on a Dell Inspiron N4010 Laptop

I have a Dell Inspiron N4010 laptop. My brightness hotkeys are not able increase or decrease the brightness of the screen. And as a matter of fact, I also can not reduce the brightness from the Brightness & Lock menu under System Settings. Any solutions?

EDIT: I think I may have found the reason behind the problem. In the previous versions of Ubuntu there were acpi_video0 and intel_backlight inside the /sys/class/backlight folder. Now in 13.04 there are dell_backlight and intel_backlight in that folder. And the most interesting part, my friend installed 13.04 on his Dell Vostro and in his system's /sys/class/backlight folder there are acpi_video0 and intel_backlight. So the brightness hotkeys are working for him.

I have the same model and I had the same problem all the way through 13.04 development until one day before release and then it started working. I filed the bug here: Bug #1105604: Brightness control stopped working

What you can do is to use a manual override that I used throughout development, by modifying /etc/rc.local as follows:

#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.
echo 978 > /sys/class/backlight/intel_backlight/brightness
chmod 777 /sys/class/backlight/intel_backlight/brightness
exit 0

The downside is that you can't change the brightness easily except by manually modifying the file /sys/class/backlight/intel_backlight/brightness

When I did have it working, I used the Fn + brightness keys to check the settings: the lowest setting is 490 and after that it goes up in increments of 488. So these are the default settings for /sys/class/backlight/intel_backlight/brightness:

490 Lowest with backlight on
978
1466
1954
2442
2930
3418
3906
4394
4882 Brightest

My brightness controls were previously working, but are broken again so I decided to create a script to manage it:

#!/bin/bash
# Dell N4010 brightness control workaround
# Note: add the following to /etc/rc.local
#       chmod 777 /sys/class/backlight/intel_backlight/brightness
# For convenience I've assigned the keys Alt-Up and Alt-Down to run this script
# Fine tune the bump parameter as required
#
# Usage:
#    ./brightchg.sh up   # bump up brightness
#    ./brightchg.sh down # bump down brightness
#
curr=`cat /sys/class/backlight/intel_backlight/brightness`
bump=244
if [ "$1" == "up" ]; then
  curr=`echo "$curr + $bump" | bc`
else
  curr=`echo "$curr - $bump" | bc`
fi
# Set the brightness to the new level making sure it's always above 30 (minimum usable)
if [ $curr -gt 30 ]; then
    echo $curr | tee /sys/class/backlight/intel_backlight/brightness
fi

Note: I added a line in /etc/rc/local to give me authority to the brightness file:

chmod 777 /sys/class/backlight/intel_backlight/brightness

Then I assigned it to the keys Alt+Up and Alt+Down as shown here: