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I'm using a macbook pro 8,1. When I use the brightness keys on the keyboard, decreasing the brightness works until it reaches the lowest brightness level. At that point (when on the lowest level), the brightness is something like 70 or 80% instead of 0-10% (or whatever it usually is). All the other levels are fine.

How can I adjust/calibrate these brightness controls?

PS: I'm currently using 12.04 but I've had the same issue no later than 11.10 (and I'm fairly confident it was present in 11.04 as well).

UPDATE: If I go to System Settings and select "Brightness and Lock" the exact same thing happens, but there is more fine grained control of the brightness. It goes to completely black when the dial is about 10% from the left edge. When it passes that point, anywhere inside that left 10% appears to be about 70 - 80% brightness (there's no change regardless of where the dial is in this section).

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+50

This is a bug in how ACPI backlighting is handled on your platform. Please install 'fwts', run the full suite, or just the backlight tests, and upload the results to a new launchpad bug.

See https://wiki.ubuntu.com/Kernel/Debugging/Backlight

Thanks.

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is this the same bug? That seems to be about not being able to adjust the backlight and other issues like that. I can adjust my backlight and it all works fine. It's just that minimum brightness is quite a bit brighter than the level right above minimum (all other levels are fine). –  greggory.hz Apr 13 '12 at 6:13
    
iirc there are special conditions for how brightness controls act at the boundaries, so if you get all to way to zero brightness and tap lower brightness twice, it might pop you back to 50% brightness. www.acpi.info/DOWNLOADS/ACPIspec40a.pdf. I used to debug this sorta stuff for a living. We may be able to work around it with a platform specific patch though, so file a bug and also contact your vendor. In the future, check out the list of certified platforms, as those have had their BIOS/ACPI hardened so these features "just work" right out of the box. ubuntu.com/certification –  ppetraki Apr 13 '12 at 13:34
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