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Old 06-12-2016, 04:24 AM   #1
werner291
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Screen brightness in Gnome 3 behaves wierd


Hello!

I just installed Debian Jessie with Gnome 3 on my MacBook to try it out, and I am very impressed with how well it performs. I'm seriously thinking about removing OSX completely.

However, the screen brightness is behaving wierdly.

When set to 90-100% brightness, it behaves normally, but around the 70-80% mark it suddenly goes from very bright to almost completely dark.

Sometimes (very inconsistently), it even starts flickering. Considering I've been installing and removing a lot of power-management-related software lately, I suspect some external program is affecting it (perhaps two at the same time that conflict with eachother?), but I'm not exactly sure which.

Is there a way I can see which programs are changing that setting?
 
Old 06-14-2016, 01:08 AM   #2
zH2L
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Check what Gnome extensions you have installed/enabled.

Also, how are you adjusting the brightness of your screen? Through the brightness buttons on your macbook? Or do you adjust the brightness via the OS only?
 
Old 06-14-2016, 03:38 PM   #3
werner291
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Hello,

I checked in the gnome tweak tool and disabled all the extentions I could find.

I also noticed I had f.lux configured to run onstartup.

Problem seems to be gone now, though I'm not sure what exactly caused it.

f.lux seemingly worked well so far, so I wasn't suspicious of it.

The problem appeared both when using the brightness keys and using the Gnome 3 brightness slider.
 
Old 06-29-2016, 04:19 AM   #4
werner291
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So, turns out it's not flux as I'm quite sure it's turned off now, and happening in KDE as well as Gnome.

Is there anything else that I could check?

EDIT: I have an Intel graphics card in case that's relevant.

Last edited by werner291; 06-29-2016 at 04:25 AM.
 
Old 06-29-2016, 04:35 AM   #5
werner291
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More info:

I went into /sys/class/backlight/intel_backlight and tried echoing values into "brightness".

Using 2228 or higher seems to give full brightness.
Using 2227 yields a wierd blinking effect.
Using 2226 also yields the blinking effect, but a lot darker.
Finally, 2225 and lower gives complete darkness.

The blinking uses a smooth transition.

It almost looks like an attempt at using PWM to dim the backlight, while some other part of the system tries to make the transition smooth. That would certainly explain the behavior.

EDIT: more info

The problem only appears after I close the laptop lid. If I reboot, the brightness behaves normally, until I close the lid. After re-opening the lid, the brightness behaves weirdly.

Last edited by werner291; 06-29-2016 at 04:54 AM.
 
  


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