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DDC/CI

The DDC/CI standard (introduced in 1998!) allows a computer to send commands to external monitors.

For instance, we can programmatically set the brightness of all our monitors:

sudo apt install ddcutil
  • create a shortcut associated with a script to switch between bright and dim:
if [ "$(cat /sys/class/backlight/intel_backlight/brightness)" = "960" ]; then
	# Set laptop monitor's brightness
	echo 57984 | sudo tee /sys/class/backlight/intel_backlight/brightness
	# Set external monitors' brightness
	sudo ddcutil setvcp 0x10 60
else
	echo 960 | sudo tee /sys/class/backlight/intel_backlight/brightness
	sudo ddcutil setvcp 0x10 0
fi

0x10 is the code for brightness. Run sudo ddcutil detect to list the monitors ddcutil can work with, and sudo ddcutil getvcp all to list the features available.

info

Because sudo is required, the shortcut's command needs to use pkexec:

pkexec /path/to/switch-brightness.sh

And by the way, here's another script, to switch between light and dark themes:

if [ "$(gsettings get org.gnome.desktop.interface gtk-theme)" = "'Yaru'" ]; then
	gsettings set org.gnome.desktop.interface color-scheme "prefer-dark"
	gsettings set org.gnome.desktop.interface gtk-theme "Yaru-dark"
else
	gsettings set org.gnome.desktop.interface color-scheme "prefer-light"
	gsettings set org.gnome.desktop.interface gtk-theme "Yaru"
fi