I am not sure if this bug is affecting me, and if I am right to post my
comment here. I am using Ubuntu 10.10 (AMD64) on a HP ENVY 14 with an
Intel i5 CPU (and integrated GPU).

The fn keys (fn+f2 and f3) for controlling the brightness do work.
However, I noticed the following:

1.) Ubuntu did start with dark screen (minimum brightness set to 0) as 
described here (http://ubuntuforums.org/showthread.php?t=1593079).
Adding "echo 2 > /sys/class/backlight/acpi_video0/brightness" to 
/etc/init.d/rc.local as sugessted did help.

2.) Settings in gnome-power-manager related to the backlight had no real
effects, except on notify-osd. For example, although
brightness_dim_battery (LCD dimming amount when on battery) was set to
50, unplugging the notebook had no effects on the brightness, but
notify-osd appeared to be reduced by a half.

3.) the notify-osd was completly out of sync; while it could only be
increased and decreased in five steps, the brightness itself could be
changed in ten steps. A similar bug was reported here
(https://bugs.launchpad.net/ubuntu/+source/notify-osd/+bug/351326).
Adding "acpi_backlight=vendor" as suggested as a solution did deactivate
the fn keys (fn+f2 and f3) completely and /sys/class/backlight became
empty. However, ubuntu did start with full-bright screen.

I am wondering now if the backlight PPA could be a solution to my
problem?

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https://bugs.launchpad.net/bugs/568611

Title:
  Screen brightness control fails on Dell Studio 1558

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