Comment 30 for bug 555122

Thank you, silvan. It worked on my HP Compaq 6735b too. I am writing below what I did. Combined from silvan's posts.

$ sudo killall gnome-power-manager
$ gnome-power-manager --verbose

I pushed brightness keys(Fn+F9/F10) on the keyboard, the brightness scale popped up on the screen

$ lshal | grep system.hardware.vendor
 system.hardware.vendor = 'Hewlett-Packard' (string)
$ lshal | grep system.hardware.product
 system.hardware.product = 'HP Compaq 6735b' (string)

$ sudo gedit /usr/share/hal/fdi/information/10freedesktop/10-laptop-panel-hardware.fdi

<match key="/org/freedesktop/Hal/devices/computer:system.hardware.vendor" string="Hewlett-Packard"> // my vendor 'Hewlett-Packard'
        <match key="/org/freedesktop/Hal/devices/computer:system.hardware.product" contains_outof="2510p;2710p;nc2400">
          <merge key="laptop_panel.brightness_in_hardware" type="bool">true</merge>
        </match>
 <match key="/org/freedesktop/Hal/devices/computer:system.hardware.product" contains_outof="6735b;4410s;4415s;4416s;Compaq 5X5"> //added '6735b' to this list
   <!-- needed since the acpi video module reports it handle the events, but it don't work on this machines-->
          <merge key="laptop_panel.brightness_in_hardware" type="bool">false</merge> //here is false
        </match>
      </match>

After that I saved the changes and rebooted.