screen-dimmer

One brightness control for all my screens — laptop + external monitors — that stays eye-matched as it dims, and rides GNOME Night Light's curve so the screens dim warm and dark together at bedtime.

GNOME natively dims only the laptop panel and only shifts color (Night Light), never the brightness of external monitors. This fills that gap.

How it works

final_brightness[screen] = base[screen]  ×  master%  ×  nightlight%

• base[screen] — per-screen calibration you set by eye (a panel at 60% can look as bright as another at 85%). Lives in ~/.config/screen-bright.conf.
• master% — one slider (screen-slider) scaling all screens together. Because it's a multiplier, the screens stay matched while you dim.
• nightlight% — read live from GNOME's gsd-color D-Bus Temperature property, so brightness follows the exact same schedule/ramp as Night Light (your fixed hours, or sunset if you switch Night Light to automatic + location).

Brightness is applied with no root at runtime:

• laptop panel → systemd-logind SetBrightness (active session)
• external monitors → DDC/CI via ddcutil (the active user gets i2c access from ddcutil's uaccess udev rule)

A systemd --user timer (screen-auto.timer, every 1 min, change-detected) keeps brightness tracking the Night Light ramp.

Install

./install.sh

Then calibrate and try the slider:

$EDITOR ~/.config/screen-bright.conf   # tune BASE_* until screens look equal
screen-slider                          # master dimmer for all screens

Bedtime / auto dim (requires Night Light)

The time-based dim rides GNOME Night Light — if Night Light is off, the master slider still works but brightness never dims on a schedule. Turn it on and set the schedule/temperature in Settings → Display → Night Light (or automatic + Location Services for real sunset). install.sh enables it for you:

gsettings set org.gnome.settings-daemon.plugins.color night-light-enabled true

Optional: bind the slider to a hotkey (Super+B)

p=/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/screendim/
gsettings set org.gnome.settings-daemon.plugins.media-keys custom-keybindings "['$p']"
gsettings set org.gnome.settings-daemon.plugins.media-keys.custom-keybinding:$p name 'Screen dimmer'
gsettings set org.gnome.settings-daemon.plugins.media-keys.custom-keybinding:$p command "$HOME/.local/bin/screen-slider"
gsettings set org.gnome.settings-daemon.plugins.media-keys.custom-keybinding:$p binding '<Super>b'

Dependencies

• ddcutil — DDC/CI brightness for external monitors (ships the i2c uaccess udev rule)
• zenity — the slider dialog (GNOME default; already present on most systems)
• GNOME (uses gsd-color + logind D-Bus), Wayland or X11

Adapting to other hardware

This is built for one machine (1 laptop + Lenovo G32qc + ARZOPA). Three spots in bin/screen-apply are hardware-specific — edit them for your setup:

What	Where	Find it with
laptop backlight device	/sys/class/backlight/amdgpu_bl1	ls /sys/class/backlight/
external monitor models	the two ddcutil --model "..." lines	ddcutil detect
per-screen base values	~/.config/screen-bright.conf	calibrate by eye

Opening the slider

Three ways, all set up by install.sh:

• Super+B hotkey
• Screen Dimmer icon in the app grid / Activities search
• screen-slider in a terminal

Commands

Command	Does
screen-slider	master slider (0–100) for all calibrated screens
screen-apply	recompute & apply base × master × nightlight (used by the timer)
screen-calibrate	snapshot each screen's current brightness as its new base
screen-dim <0-100>	low-level: same absolute % on all screens, ignores calibration

Calibrating

BASE_* in the config is each screen's ceiling — the slider and Night Light only scale down from it. Two ways to set them:

• By eye, then snapshot: match the screens with their physical OSD buttons (at master 100, daytime), then capture — click Snapshot as base in the slider, or run screen-calibrate. Both write the current brightness into the config as the bases.
• By hand: edit ~/.config/screen-bright.conf and run screen-apply.

ARZOPA quirk: it blacks out above 73% (tested). ARZOPA_MAX (default 73) is a hard ceiling clamped in screen-apply — keep BASE_ARZOPA ≤ it.

Notes / limitations

• zenity --scale is one-shot (drag → OK → applies), not live-drag. External monitors dim slowly over DDC/CI anyway, so live drag would lag/flicker. Swap in yad --scale --print-partial if you want continuous drag.
• Laptop displays don't support DDC/CI — that's why the laptop uses logind, the externals use ddcutil.
• If externals report Permission denied right after install, log out/in once.

Uninstall

systemctl --user disable --now screen-auto.timer
rm ~/.local/bin/{screen-apply,screen-slider,screen-dim}
rm ~/.config/systemd/user/screen-auto.{service,timer}
rm ~/.config/screen-bright.conf
rm ~/.local/share/applications/screen-dimmer.desktop
gsettings reset org.gnome.settings-daemon.plugins.media-keys custom-keybindings   # drops the Super+B entry
systemctl --user daemon-reload

(Night Light, Location, and /etc/modules-load.d/i2c-dev.conf are left as-is — they're GNOME/system settings, not owned by this tool.)