Screen brightness ignores AC power in 11.10

[Gannin]

With 11.10, if I do not have the AC power plugged in, the screen is dim. If I plug the AC power in, the screen remains dim.

This worked with past versions of Ubuntu (10.10, 11.04). In past versions of Ubuntu, if I plugged in AC power, the screen would brighten up, and then if I unplugged AC power, the screen would dim to conserve battery.

Now the screen stays dim regardless of if AC power is plugged in or not. And if you adjust the brightness manually in System Settings, it doesn't save the change when you reboot.

[Gannin (spacesword)]

To add more information, I went to the Drivers module to try to enable the FGLRX driver for my ATI card and it wouldn't, and still won't, install. After downloading the driver it puts up an error message. However, since trying to install it, even though it wouldn't install, now the screen brightness works as it should. Unplug the AC and let it sit for a moment and it gets dim, plug the AC back in and it stays bright. Strange.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Christopher O. Nash (conwrite)]

This is kind of important for me. It usually takes me a couple a times to get the brightness just right. Use it for a while and then make adjustments. This is no big deal if after I'm satisfied with it, it stays set, but my adjustments are lost every time I restart which SUCKS! Too bright or too dim after a while gives me a headache. :-(

[spencer davies (bogwelsh)]

Same problems on HPG62 laptop...
1. plugging/unplugging external power has no effect on brightness
2. screen brightness setting returns to maximum after suspend or reboot

[Dave Jones (dgjones)]

I get the same problem with a HP G72 laptop, Intel HD graphics.

Screen brightness is set to minimum at boot regardless of mains/battery power.

[Christopher O. Nash (conwrite)]

Just to add... I upgraded my netbook yesterday to 11.10 and oddly enough, that always starts at full brightness which is the opposite of my laptop that I referred to above that always starts at max dimness. My laptop is a G72 like Dave's and my netbook is one of the old Acer models. Hope that helps in some way.

[snowguy (snowguy)]

In case there are others that had the same misunderstanding I had...I thought this bug affects me but it turns out it doesn't. First after reboot I can see that my brightness settings are not lost on reboot (the 2nd part of this bug). However I still believed the first part of the bug affected me since I couldn't see how to distinguish the brightness setting when I was on AC vs when I was on battery.

However, after some testing I found that different brightness settings for AC and batter do work (at least for me) ...it is just extremely unintuitive. Try this to see if, like me, this bug doesn't affect you.

Go into brightness setting on AC. set it all the way up to the top. Close the brightness settings window.
Now unplug your laptop. Now go back into the brightness setting and set it to be medium brightness. Close the brightness window.

Now plug your laptop in and then unplug it. If this is working for you, as it does for me, you'll notice a visible difference in the brightness setting for your screen.

[Ernesto Torresin (ewk)]

On a Dell Latitude D610, booting with kernel 2.6.38-11-generic instead of 3.0.0-12-generic seemed to solve the problem for me.

[Marco Parillo (marco-parillo)]

Upgrading to 12.04 solved my problem.
https://answers.launchpad.net/ubuntu/+source/acpi/+question/174296

[Marco Parillo (marco-parillo)]

Closing the bug based on comment 9