how to change Backlight-Brightness

[Raphael Brunner <lilo-@gmx.ch>]

Hi Users

i have a HP pavilion dv9294ea Notebook with Nvidia geforce go 7600
inside. I installed debian testing (actual) on it and it works fine.
But one problem is, the key to change backlight-brightness don't work.
If the notebook is powered from grid, then the light is full brightness,
and if it's powered from accu, the light is very weak (I think the
minimum).

I have the nvidia driver from aptitude and all works find (also opengl).
Also the newest nvidia-driver from their homepage don't work the
backlight. I tried also "nvclock -S xx". But, the output say, i changed
the value to xx, but nothing changed real on the display.

Has onyone the same problem or possible a solution for this problem?

I don't know where to start debugging...

Thanks a lot for all ideas and help.
Raphael