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I'm currently using a LG laptop with Nvidia Cuda GeForce GT 335M.

I have difficulty adjusting the screen brightness using FN+Arrow Up/Arrow Down. The brightness indicator will appear and the bar will not decrease beyond the first jump. Subsequently, if I depress the button, the indicator bar will randomly appear to be dim and bright, with no actual difference to the screen brightness.

I have tried to adjust the brightness through System Settings>Screen. Although the bar can be dragged up and down, there seems to be no actual difference in the brightness.

Furthermore, after installing Ubuntu 11.10, I have difficulty adjusting the brightness in Windows 7 as well. The function button does not respond at all, and adjusting it through the Control Panel does not seems to have any actual difference.

What could be the problem?

I have tried to edit the /etc/X11/xorg.conf, and add the line Option "RegistryDwords" "EnableBrightnessControl=1", but it is not working for me.

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3 Answers 3

Try this: http://askubuntu.com/a/120796/54126 Confirmed working solution on clean Ubuntu 12.04 beta2 with 3.2.0-22 kernel with latest nvidia drivers. FN keys work, no need to make changes in grub or Xorg.conf

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If the button is not working either in ubuntu or windows, then the problem may be coming from the button itself rather than ubuntu. I would have that button checked, maybe it is buged or some connection to the motherboard went MIA.

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Hi, the button is definitely working. The problem here is that the brightness does not change with the input of the button, and the on-screen indicator of screen brightness refuses to change or have some random change which does not correspond to any actual difference in screen brightness. –  Tan Zhong Xian Jan 8 '12 at 15:50
    
The button IS working but not properly....Maybe get it checked –  Jester Jan 8 '12 at 22:40
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try this on your terminal.

sudo setpci -s 00:02.0 F4.B=50
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Hi, what does this command do? Nevertheless, I tried, but the terminal returns setpci: Warning: No devices selected for "F4.B=50" –  Tan Zhong Xian Jan 8 '12 at 15:50
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