Solar Screen

Solar-position display white-point controller for GNOME on X11.

Solar Screen estimates clear-sky direct sunlight at the configured location, maps its chromaticity onto an sRGB display, and applies the result through an atomic XRandR gamma ramp. It does not change hardware brightness.

At night, the controller transitions from the modeled horizon white point to red-only output. The default red-only threshold is -6° solar elevation.

Requirements

• Linux with an X11 session
• GNOME and systemd user services
• Python 3.10+
• libX11, libXrandr, gsettings, and gdbus

Wayland is not currently supported.

Install

git clone https://github.com/juanfradb/solar-screen.git
cd solar-screen
mkdir -p ~/.local/bin ~/.config/solar-screen
ln -sfn "$PWD/solar_screen.py" ~/.local/bin/solar-screen
cp config.example.json ~/.config/solar-screen/config.json
chmod +x solar_screen.py

Edit ~/.config/solar-screen/config.json with latitude, longitude, and altitude, then enable the service:

solar-screen enable

Control

solar-screen status
solar-screen disable
solar-screen enable

enable saves and disables GNOME Night Light before taking ownership of the display LUT. disable restores the exact baseline LUT and the previous GNOME Night Light setting.

Model

• NOAA apparent solar elevation, calculated in UTC every five seconds.
• Bird SPECTRL2 clear-sky direct-normal spectral irradiance.
• CIE 1931 2° color matching functions and sRGB conversion.
• Exact sRGB EOTF/OETF composition over the existing XRandR baseline.
• Smooth twilight transition to red-only output.

The runtime has no Python package dependencies and works offline. The bundled lookup table was generated with pvlib and colour-science; its reproducible generator is in tools/generate_solar_table.py.

A three-primary LCD cannot reproduce a full spectral power distribution. This project reproduces the closest display chromaticity available from its fixed RGB primaries. Cloud percentage is intentionally excluded because it does not determine spectral composition.

Verify

python3 -m unittest -v
systemd-analyze --user verify solar-screen.service

License

MIT