Cannot adjust screen brightness on laptop

I have a Acer Aspire 5738Z laptop which I have just updated to 10.04. I cannot adjust the screen brightness either. On my machine the screen should be adjustable by using the window key and the left and right arrows. Pressing them does bring up a slider control which can be adjusted but it makes no difference to the actual brightness. The panel applet behaves exactly the same and makes not difference to the brightness.

I have the same problem with my Dell Vostro 3500/NV310M/. (ubuntu 10.04, Nvidia driver 195.36.15)
The brightness of screen is set at 100%.
I try to change it manually, "echo -n 30 >/proc/acpi/video/PEGP/LCD/brightness ". The value in ../brightness file was changed but the screen didn't change brightness.

Sorry for my english. :)

Yes, I have the same problem with my Toshiba T110 - the screen brightness should dim/brighten with the function keys but as with other comments, pressing them does bring up a slider control which can be adjusted but it makes no difference to the actual brightness.

one more: i experience the problem with lucid on an asus k70ij
function keys don't work, sometimes a slider appears after some seconds, but brightness remains at 100%
neither the "echo -n 30 >/proc/acpi/video/PEGP/LCD/brightness" command works for me
i found that "setpci -s 00:02.0 F4.B=11" does the job, but the problem is that in an unpredictable manner, brightness suddenly gets back to the maximum
doh!

The same problem I have in my Compaq Presario CQ60. I can add that that applet worked fine in 9.10, using both: function keys or mouse with the applet in the panel I have.

I add myself to this bunch. Exactly the same with Ubuntu 10.04 LTS 32-bit. It is a HP/Compaq 615.

Changing the slider on the applet does not have any visible effect.
The Function Keys controlling the brightness have no effect and fail to control the slider.
The brightness is set to maximum.

When plugging in the cable and removing it, thereby running on battery, the screen dims a step. Repeating the process the screen continues to being dimmed. There is no possibility to brighten it up again. So having done this a couple of times the screen is nearly dark. Rebooting the system, the screen brightness is back to maximum.

Can I help with some more info? BTW.: I am Linux newbie but with a high level of comprehension. Taught myself on computers since early 90's.

Thank you anybody helping us out on this one.

@moderator: Please remove the answer flag from this one - It is far from being answered at all! Thanks.

Yep, same here - a new duel boot 10.04 install on a Asus 1005PE and the screen brightness control does not work either.
Windows XP is happy and the GRUB loader works dandy and sees both installs but the Ubuntu desktop screen is very dark and if you try to adjust it, the screen brightness goes up and down and off in no real order - its not happy. I'd say its deff a bug! 10.04 Lynx is not happy but I ran 9.10 Koala on the Mini 1005PE for 9 months and it was great.

Cheers'
Dave

In previous distributions the Lightness Applet worked fine on my Dell XPS M2010. It stopped working properly after installing Lucid. Clicking on the applet causes the scroll bar to disappear (it used to jump to the far left side of the screen until I installed a recent update to Lucid). I learned from another posting that the up and down arrow keys adjust brightness. That seems to work, so do that until the applet is fixed: Click on the Brightness Applet so the vertical scroll bar is displayed; then use the up and down arrow keyboard keys.

Or the other option is to .... nuke and pave 10.04 Lynx and re-install Koala on the same partition like I did yesterday. (grin)
Someone said it's becasue they play with the frame buffer .... I'm sure they'll fix it eventually anyway but in the meantime going back to 9.10 is no biggie for me and it's happy as a clam !

Cheers'
Dave

Thanks Adrien Crivelli, that solved my question.

@moderator: Please remove the answer flag from this one - It is far from being answered at all! Thanks.

I agree this not solved. I merely provided a workaround (http://ubuntuforums.org/showpost.php?p=9429211&postcount=19) which I am not pleased to have to use. This probably need real debugging.

I would be gald to provide logs or whatever info may be necessary if someone tells me what/how.

I have dell vostro 3500 and added this line to my /etc/Xorg/xorg.conf

    Option "RegistryDwords" "EnableBrightnessControl=1"

in Section "device"

this solved the issue for me.

It worked for me as well on my Vostro 3500 (after a reboot). Thanks !

Do you have nvidia drivers for 64 bit ubuntu?

I believe it is but cannot fint out for sure. The "NVIDIA X Server Settings" dialog shows:
Operating System: Linux-x86_64
NVIDIA Driver Version: 195.36.24

Let me know how to find out more, if it is needed.

JohnB (Original poster), I have just noticed a similar problem, that the slider disappears as soon as I click on it. HOWEVER, I have found that it seems to be a GUI problem. If I click on the applet to make the slider appear, then RIGHT-click on it (the context-menu will then appear), then left-click back on the slider, it will then work. I have no idea why, but this seems to be a GUI bug. Hopefully, this helps some others out there as well.

Thanks Ochach, it works (after reboot) Samsung r700 ))