I am trying to change the screen brightness.

I've already tried:

  • Loading acpi_video with kldload.

    The module loads fine however sysctl hw.acpi.video prints only:

    sysctl: unknown oid 'hw.acpi.video'

  • Adding Option "RegistryDwords" "EnableBrightnessControl=1" to the Device section. It doesn't work. Rebooting didn't help.

  • Running xbacklight(1).

  • Installing nvidia-settings. It seems like I cannot control the brightness from there.


  • uname -a returns:

    FreeBSD pc 10.3-RELEASE-p4 FreeBSD 10.3-RELEASE-p4 #0: Sat May 28 12:23:44 UTC 2016 root@amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC amd64

  • The machine is Dell XPS L702X.

  • The graphic card is NVIDIA GT550M.

  • I use an external Samsung 2043NW display.

Related threads


I wasn't able to use xbacklight(1) and activate the brightness control keys but I've found a couple of other ways to change the brightness:

  1. xrandr(1)

    Thanks to How to change LCD intensivity/brightness I was able to change the brightness of the external monitor using xrandr. The command looks like this:

    xrandr --output HDMI-0 --brightness 0.9

    The default value seems to be 1.

  2. redshift(1)

    Redshift is a software allowing you to change the temperature of your screen. It has -b, -t and -g options which might come handy (see man redshift for more details).

One way or another, I would still like to know if it is possible to use xbacklight on this machine.

It looks like the problem with colors might be caused by the fact that I connect the monitor over a VGA-HDMI adapter. HDMI seem to mess up the colors of a connected monitor this way.

I've found a solution to this problem: Yellow and gray blend with white on a remote monitor connected with a HDMI-VGA adapter


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