Candela

Manual brightness and color temperature control for Linux — named after the SI unit of luminous intensity.

A clean, dark-themed desktop utility for tuning your monitor at night (or any time). Two sliders: one for brightness, one for color temperature in Kelvin. No automatic scheduling, no daemons — just instant manual control when you want it.

Why Candela?

Most Linux tools in this space are either time-based and automatic (Redshift, Gammastep), command-line only (xrandr, sct), or have dated UIs that expose raw R/G/B gamma channels instead of a human-friendly Kelvin temperature slider. Candela aims to be the tool you reach for when you just want to quickly dim your screen and warm the color for late-night use.

Features

• Brightness slider — 10% to 100%
• Color temperature slider — 2000K (warm candlelight) to 6500K (daylight)
• Multi-monitor support — dropdown auto-populated from connected outputs
• Instant apply — changes take effect as you move the slider
• Settings persist after closing, within your X session (until logout/reboot)
• Reset to Defaults button restores 6500K / 100% brightness
• Dark UI — easy on the eyes when you need it most

Requirements

Python: 3.10+

Python packages:

pip install PyQt6

System packages:

sudo apt install redshift        # Debian / Ubuntu / Mint
sudo dnf install redshift        # Fedora
sudo pacman -S redshift          # Arch / Manjaro

redshift handles color temperature. Brightness works without it (software gamma via xrandr).

Note: X11 only. Wayland is not currently supported.

Install

git clone https://github.com/jfblanchard/candela.git
cd candela
pip install PyQt6
python candela.py

Install via pip

pip install candela-ctrl
candela

Build a standalone binary

pip install pyinstaller
pyinstaller --onefile --windowed --name candela candela.py
# Produces: dist/candela  — single executable, no Python required

Contributing

Issues and PRs welcome. If your monitor supports DDC/CI, hardware brightness control (via ddcutil) is the next planned feature — real backlight reduction instead of software gamma.

License

MIT