Screen is brighter on MacOSX than on Linux

[Sylvain Joyeux <sylvain.joyeux@m4x.org>]

I have the feeling that the LCD is brighter when I'm on OSX than when I'm on 
Linux. At least, I do find it too dark.

I saw in the radeon fb driver that the backlight wasn't fully ON on purpose, 
but I don't know what the values mean here (and I'd like to avoid breaking my 
LCD :p)

I have an 12" iBook G4 800

Thanks in advance for any information
--
Sylvain Joyeux