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Try

echo 4 > /sys/class/backlight/acpi_video0/brightness

That will set brightness to 40%. You may need to change the directory to match your video card.

xbacklight can be also helpful, e.g.

xbacklight -d :0 -dec 30

should decrease brightness by 30%.

Be aware that these two are hardware modification (people usually prefer that to manipulate screen brightness), and your initial command xrandr --brightnes uses software to manipulate gamma. The screen may or may not look exactly the same after applying these different techniques.

Try

echo 4 > /sys/class/backlight/acpi_video0/brightness

That will set brightness to 40%. You may need to change the directory to match your video card. Note also that you'll have to be in the video group.

xbacklight can be also helpful, e.g.

xbacklight -d :0 -dec 30

should decrease brightness by 30%.

Be aware that these two are hardware modification (people usually prefer that to manipulate screen brightness), and your initial command xrandr --brightnes uses software to manipulate gamma. The screen may or may not look exactly the same after applying these different techniques.

Try

echo 4 > /sys/class/backlight/acpi_video0/brightness

You may need to change the directory to match your video card.

xbacklight can be also helpful, e.g.

xbacklight -d :0 -dec 30

should decrease brightness by 30%.

Try

echo 4 > /sys/class/backlight/acpi_video0/brightness

That will set brightness to 40%. You may need to change the directory to match your video card.

xbacklight can be also helpful, e.g.

xbacklight -d :0 -dec 30

should decrease brightness by 30%.

Be aware that these two are hardware modification (people usually prefer that to manipulate screen brightness), and your initial command xrandr --brightnes uses software to manipulate gamma. The screen may or may not look exactly the same after applying these different techniques.

Try

echo 4 > /sys/class/backlight/acpi_video0/brightness

You may need to change the directory to match your video card.

xbacklight can be also helpful, e.g.

xbacklight -dec 30

should decrease brightness by 30%.

Try

echo 4 > /sys/class/backlight/acpi_video0/brightness

You may need to change the directory to match your video card.

xbacklight can be also helpful, e.g.

xbacklight -d :0 -dec 30

should decrease brightness by 30%.