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How to change brightness of LCD want image look deemed and soft the

xrandr --output LVDS1 --gamma 0.8:0.8:1.1

change only gamma but not the brightness of image. I have no option --brightness for xrandr

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From man xrandr (this is not listed in the -h options, but it works for me):

--brightness brightness

Multiply the gamma values on the crtc currently attached to the output to specified floating value. Useful for overly bright or overly dim outputs. However, this is a software only modification, if your hardware has support to actually change the brightness, you will probably prefer to use xbacklight.

I don't know if there is a universal standard for manipulating LCD brightness; if not this will become a matter of hardware drivers, etc.

Which I suspect it is; trying xbacklight -get on my philips LED gave:

»xbacklight -get
No outputs have backlight property

Guess I am stuck using the gimpy buttons on the panel. ;)

BTW: xrandr --brightness does exactly the same thing as using three identical values with --gamma.

  • This is great. Works on FreeBSD even when xbacklight(1) doesn't! – Mateusz Piotrowski Sep 15 '16 at 21:29
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If someone should stumble upon this but meant to look for a way to set backlight through xrandr:


$ xrandr --verbose gives some hints:

$ xrandr --verbose
Screen 0: ...
...
    BACKLIGHT: 268 
        range: (0, 852)
    Backlight: 268 
        range: (0, 852)
...

There is some property or variable BACKLIGHT; hopefully it can be set.

Reading from $ man 1 xrandr reveals a --set <property> <value> option. So there we have it:

$ xrandr --output <output> --set BACKLIGHT <value>

I use this to increase/decrease my backlight in about 1/40 steps:

$ xrandr --output eDP1 --set BACKLIGHT $(( $(xrandr --prop | awk '/^eDP1/,/^DP1/{if ($1 ~ /BACKLIGHT/) {print $NF; exit} }') + (852/40) ))
$ xrandr --output eDP1 --set BACKLIGHT $(( $(xrandr --prop | awk '/^eDP1/,/^DP1/{if ($1 ~ /BACKLIGHT/) {print $NF; exit} }') - (852/40) ))
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Neither of the solutions above were sufficient for me.

Use the below to find which backlights are available.

ls /sys/class/backlight/

In my case there was a folder intel_backlight in that folder.

Look for the max brightness file, it will let you know the upper bound you can set your brightness to, in my case this file:

/sys/class/backlight/intel_backlight/max_brightness

Set the brightness to max:

cat /sys/class/backlight/intel_backlight/max_brightness | sudo tee /sys/class/backlight/intel_backlight/brightness

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