Without using a 3rd party program

As of version 0.13.0, you do not need a 3rd party program to adjust your display brightness.
However, your user will need a few extra permissions.

Laptop displays

Laptop displays are adjusted by reading and writing to the files in the /sys/class/backlight directory. To avoid having to run this library as root every time, you can do the following:

1. Add a udev rule to allow editing of the brightness files.
   This command adds a line to your backlight udev rules allowing you to write brightness values to the relevant files.

   echo 'SUBSYSTEM=="backlight",RUN+="/bin/chmod 666 /sys/class/backlight/%k/brightness /sys/class/backlight/%k/bl_power"' | sudo tee -a /etc/udev/rules.d/backlight-permissions.rules
   

2. Reload udev rules

   sudo udevadm control --reload-rules && udevadm trigger
   

3. If the above steps don't immediately work, reboot.

Credit to Nayr438's comment on the LTT forums for this.

Desktop displays

Desktop displays are dealt with by reading and writing to the I2C buses, located at /dev/i2c* on a Linux system. These are usually part of an i2c user group, which you can check by running the command ls -lh /dev/i2c*.

If you add yourself to the i2c group your user should be able to read from and write to the I2C buses without needing to use sudo. To add youself to the i2c group, run the following command:

usermod -a -G i2c [your username here]

The I2C permissions section of the DDCUtil docs has some more details on this process.

Using 3rd Party Programs

Supported Programs

There are a number of external programs that screen_brightness_control can call upon if the native methods fail. The advantage of using external programs is that, because they are installed using sudo apt install ..., they usually allow users to adjust the backlight without having to manually fiddle with permissions. However, they do need to be installed.

Here is an outline of all of the external programs that screen_brightness_control can call upon:

Program	Works on laptop displays	Works on external monitors	Per-display brightness control	Requires Special Permissions After Install
ddcutil	No	Yes (slowest) [1]	Yes	Read/write access for /dev/i2c* (see above)
xrandr [2]	Yes	Yes	Yes	No
light [3]	Yes	No	Yes	User must be in the video group [4]
[No program]	Yes	Yes (slow)	Yes	See above

Footnotes

[1] While both DDCUtil and the 1st party linux.I2C class do similar things over the same interface (I2C), DDCUtil also supports communicating with monitors that implement the Monitor Control Command Set over USB

[2] Xrandr has two key limitations. It doesn't support Wayland and it doesn't actually change the backlight of the display, it just changes the brightness by applying a filter to the pixels to make them look dimmer/brighter.

[3] This method is deprecated as the original Light project was archived in April 2023 and the repository has since been deleted. Unofficial packages are still available for some distros.

[4] You can add yourself to the video user group by running sudo usermod -a -G video [your username] and then logging out and back in again for the changes to take effect.

Install Instructions

• Arch
  • Xrandr: sudo pacman -S xorg-xrandr
  • DDCUtil: sudo pacman -S ddcutil
  • Light: sudo pacman -S light-git
• Debian/Ubuntu
  • XRandr: sudo apt install x11-xserver-utils
  • DDCUtil: sudo apt install ddcutil
  • Light: sudo apt install light
• Fedora
  • Xrandr: sudo dnf install libXrandr
  • DDCUtil: sudo dnf install ddcutil
  • Light: sudo dnf install light