About LCD Brightness Control

Hi
      I want to develop an application about LCD brightness control in the
platform of Windows XP SP1.
As mentioned in online MSDN which released in February 2003, some APIs, like
IOCTL_VIDEO_QUERY_DISPLAY_BRIGHTNESS and IOCTL_VIDEO_SET_DISPLAY_BRIGHTNESS,
can be useful for my development. But the outcome of my application is not 
desired, which means that the APIs may not work correctly. I have no idea to
solve this problem, so can anyone give me a hand ??
Thanks a lot !! 

Jack

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