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#1 2018-01-02 22:15:30

elifarley
Member
From: Rio de Janeiro
Registered: 2008-03-07
Posts: 37
Website

[SOLVED] Intel screen brightness doesn't change

I have a Lenovo IdeaPad Z400 Touch.

When I press the keys to increase or decrease the screen brightness, the values I read on

/sys/class/backlight/intel_backlight/brightness

do change, but the real brightness doesn't.

This laptop has an Intel HD Graphics 4000 integrated graphics controller but it also has a Nvidia GeForce GT 635M controller.

Maybe having 2 graphics controllers is causing this problem...

Any advice?

SOLUTION: In my case, acpi_backlight=vendor did the trick.

lspci | grep VGA
00:02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor Graphics Controller (rev 09)

uname -a
Linux ideapad 4.14.6-1-ARCH #1 SMP PREEMPT Thu Dec 14 21:26:16 UTC 2017 x86_64 GNU/Linux

ls /sys/class/backlight/
intel_backlight

cat /sys/class/backlight/intel_backlight/max_brightness 
976

cat /sys/class/backlight/intel_backlight/brightness
976

xbacklight -set 100
No protocol specified
RANDR Query Version returned error -1

Last edited by elifarley (2018-01-04 14:07:11)

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#2 2018-01-03 07:59:23

olive
Member
From: Belgium
Registered: 2008-06-22
Posts: 1,461

Re: [SOLVED] Intel screen brightness doesn't change

On another laptop (an older HP elitebook 2560p), I had problem due to some conflict with the intel backlight and acpi backlight and I fixed by passing acpi_backlight=native to the kernel command line. I see other parameters in the wiki. Can you try to use these parameters and see if it works. You can try also to change the acpi backlight (do a find /sys -iname "*bright*") to find all the methods in your laptop. It is usually a good idea to keep only one method (using acpi_backlight kernel command line).

Also my laptop has a ambient light sensor that gives problems with Linux. Since I don't need it, I disabled it in the firmware.

Last edited by olive (2018-01-04 08:29:41)

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#3 2018-01-04 14:03:35

elifarley
Member
From: Rio de Janeiro
Registered: 2008-03-07
Posts: 37
Website

Re: [SOLVED] Intel screen brightness doesn't change

The option acpi_backlight=vendor did the trick for me, thanks!

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