Luz

Warm your screen at night, from the tray. Like f.lux, in one small app, on Windows, macOS and Linux.

Website  |  Download

Luz is Portuguese for light.

Luz is a sun in the tray. At sunset it turns your screen's colour from daylight to a warm, lamp-like light, more slowly than you'll notice, and in the morning it turns it back. With Bedtime mode it goes warmer still before you sleep. It works out sunrise and sunset for where you are, and it has f.lux's colours and keyboard shortcuts, so if you're coming from f.lux nothing has to be relearned.

It's one small executable (under 1 MB) with nothing else to install. It doesn't ask for your location and doesn't use the network.

The sun

Sun	Daytime. Your screen looks the way it always does.
Sun going down	Evening, after sunset. The screen is warm.
Moon	Bedtime mode. Warmer still, until you wake.
Sun struck through	Paused. Your screen is back to its own colours for now.

On Windows the sun and moon are filled with the colour your screen is turning, so you can tell at a glance. Either click opens the menu.

Running luz again while it's already in the tray pauses it for an hour, or resumes it if it's paused. Pin it to the taskbar, or open Luz.app again on macOS, and that's a switch for a moment of true colour.

The menu

The top line says where Luz is right now (Evening · 3400 K), and the line under it says what comes next (Bedtime at 23:00). Under them:

Pause for an hour	Back to your screen's own colours for an hour, for photos or design work. While paused, this reads Resume.
Pause until sunrise	Off for the rest of the night. With Bedtime mode on it's Pause until morning, at your wake time.
Back to the schedule	Drops your adjustments. They also go by themselves at the next change, so a nudge at 21:00 lasts until bedtime. Only there while you've adjusted.
Adjust	Warmer and Cooler, a step at a time on top of the schedule. Dimmer and Brighter turn your monitors' own backlight down or up, 10% at a time; where no monitor lets Luz do that, they darken the picture instead, down to 30%. More below.
Brightness	Each monitor's backlight level, with 100, 75, 50, 25 and 0% to pick from. Only there when a monitor answers.
Colours	The Daytime, Sunset and Bedtime colours, from f.lux's list: Daylight 6500 K, Sunlight 5500 K, Fluorescent 4200 K, Halogen 3400 K, Incandescent 2700 K, Candle 1900 K, Ember 1200 K, and a few in between.

Settings holds the things you set once:

Location	Where Luz thinks you are. More below.
Bedtime mode	On or off, and when it starts.
Wake time	When Bedtime mode ends.
Transitions	Slow fades over an hour, the way the light outside changes. Fast takes 20 seconds.
Keyboard shortcuts	f.lux's, system-wide. More below.
Run at login	Just for your user, no admin needed. On macOS it shows up in System Settings > General > Login Items. Move Luz.app to Applications first.
Edit settings file…	Opens the config file in a text editor (⌘, on macOS). More below.

Under that is the version you're running, and Check for updates… opens Luz's web page in your browser with that version, and the page asks GitHub whether there's a newer one. Luz itself still doesn't use the network. Quit Luz (⌘Q on macOS), next to Settings, puts your screen's colours back as it goes.

The day

Two fades, each taking an hour (or 20 seconds on Fast):

• At sunset, from the Daytime colour to the Sunset colour.
• At bedtime, with Bedtime mode on, from there to the Bedtime colour. It stays that way until your wake time, then fades back.

Mornings start at sunrise. With Bedtime mode on they wait for your wake time if it's later, so a 5 o'clock dawn in June doesn't light up your screen before you're up. Each fade starts at its moment rather than finishing at it, as f.lux's do. Colours fade in mireds, the scale the eye sees as even, so a fade doesn't seem to hurry at the warm end.

Every change fades, including the ones you make. Pausing takes two seconds, and a step warmer takes less than half a second.

Where you are

Luz needs to know roughly where you are to know when the sun sets there. It guesses from your time zone. Every time zone is named after a city, and tzdata, the time zone database every OS ships, knows where that city is. That's usually close enough. A big time zone can put you a few hundred kilometres out, which moves sunset by a few minutes. There's no location prompt and nothing goes over the network.

To be exact, give it your coordinates (south and west are negative):

luz location -23.55 -46.63     # São Paulo
luz location auto              # back to the time zone's city

That writes to the config file, and a Luz that's already running picks it up within a second.

Brightness

Luz can turn down the light itself, not just its colour. Most external monitors take brightness commands over DDC/CI, the same channel their own buttons use, and Luz sends them there. That's better than darkening the picture: the backlight really dims, so there's less glare, and blacks stay black.

Monitors that answer show up under Brightness, and Dimmer and Brighter (Alt+PgDn and Alt+PgUp) move all of them 10% at a time. The level is the monitor's own setting, so it stays where you put it, even after Luz quits.

Laptop screens don't speak DDC/CI; their brightness keys already do this. Neither do some docks, USB-C adapters and TVs, and some monitors have DDC/CI switched off in their on-screen menu. With no monitor answering, Dimmer and Brighter darken the picture with the gamma ramp instead, and that lasts until the schedule next changes. On macOS and Linux this is the only kind for now: monitor brightness there needs private system services or /dev/i2c access, and isn't in Luz yet. GNOME and KDE on Wayland can't darken the picture either (see Linux), so there Dimmer and Brighter do nothing.

Keyboard shortcuts

The same keys as f.lux, so your muscle memory still works:

Windows, Linux	macOS
Alt+End	⌥End	Pause for an hour, or resume
Alt+Shift+PgDn	⌥⇧⇟	Warmer
Alt+Shift+PgUp	⌥⇧⇞	Cooler
Alt+PgDn	⌥⇟	Dimmer (monitors' backlight where they answer)
Alt+PgUp	⌥⇞	Brighter

On a Mac laptop, End and Page Up/Down are fn with the arrow keys. If another app already has one of these (usually f.lux itself), Luz skips that one and the rest still work. On Linux the shortcuts need X11; a Wayland session doesn't let apps listen for keys system-wide.

Coming from f.lux

Quit f.lux first, and turn off its Start with Windows or login item. Two apps setting your screen's colour take turns several times a minute, and you'll see it flicker. If f.lux is running when Luz starts, Luz tells you once.

Windows' Night light and macOS's Night Shift work differently: they sit on top of what Luz does, so with either one on you get both. Turn them off too.

From a terminal

luz status                    # the colour now, the day's sun, and where Luz thinks you are
luz location -23.55 -46.63    # set where you are (south and west negative)
luz location auto             # back to guessing from the time zone
luz reset                     # put the screens' colours back, after a crash
luz                           # pause the running copy for an hour, or resume it

Install

Windows

scoop bucket add kidchenko https://github.com/kidchenko/scoop-bucket
scoop install kidchenko/luz

winget and Chocolatey packages are on the way.

Or grab Luz-Setup.exe directly. Each release also ships a portable luz-x.y.z-x64.exe that runs without installing; see Releases.

The installer can also do something the portable copy can't on its own: lift Windows' limit on how warm the screen may go. More below.

The app isn't code-signed yet, so SmartScreen warns you the first time you run it. Click More info, then Run anyway.

macOS

brew install --cask kidchenko/tap/luz

Or download Luz.dmg (Apple silicon and Intel), open it, and drag Luz into Applications. It lives in the menu bar and doesn't show up in the Dock.

The app isn't notarized yet, so macOS blocks it the first time you open it. Homebrew takes care of that for you. Otherwise, do one of these once:

• Go to System Settings > Privacy & Security and click Open Anyway next to Luz.
• Run xattr -dr com.apple.quarantine /Applications/Luz.app

Move it into Applications before you do this. It won't work while the app is still inside the disk image.

Linux

curl -L https://github.com/kidchenko/luz/releases/latest/download/luz-x86_64-linux.tar.gz | tar xz
./luz/luz

Put luz/luz wherever you keep programs (~/.local/bin is a good place) before you switch on Run at login in Settings, which starts it with your desktop from then on.

It needs GTK 3 and the AppIndicator library for its tray icon. Most desktops have both already; if no sun shows up, install it:

sudo apt install libayatana-appindicator3-1      # Debian, Ubuntu, Mint
sudo dnf install libayatana-appindicator-gtk3    # Fedora

GNOME hides tray icons unless the AppIndicator extension is on. Ubuntu turns it on for you; elsewhere, install AppIndicator and KStatusNotifierItem Support.

How Luz changes the colour depends on the session:

X11, any desktop	Gamma ramps, just like Windows and macOS.
Hyprland, Sway and other wlroots compositors (niri, river, labwc)	Gamma ramps too, through the compositor's gamma control. Everything but the keyboard shortcuts works. The compositor puts its own colours back the moment Luz quits, crash or not.
GNOME on Wayland	GNOME keeps the ramps to itself, so Luz drives GNOME's own Night Light instead: always on at Luz's colour, off for daylight. Dimmer and Brighter can't work through it. Your Night Light settings are saved first and put back when Luz quits.
KDE Plasma 6 on Wayland	The same, with KDE's Night Light (in kwinrc).
Other Wayland desktops	Not yet. Luz says so in its menu.

To check which you have: echo $XDG_SESSION_TYPE.

Only one app can hold a screen's gamma at a time, so quit wlsunset or gammastep first (Luz says so if it finds one running). On Omarchy, its own Nightlight toggle is hyprsunset, which tints on top of Luz rather than taking turns with it: leave that toggle off. The tray icon shows up in Waybar's tray, which Omarchy, and most Hyprland and Sway setups, already have.

Requirements

Windows 10 or later. macOS 11 or later. Linux on x86_64 with glibc 2.35 or later (Ubuntu 22.04, Debian 12, Fedora 36), on X11, a wlroots compositor, GNOME or KDE Plasma 6.

How it works

Every screen has a gamma ramp: a table the graphics card passes each red, green and blue value through on its way to the screen. Luz writes a table that turns blue and green down by just enough to match the colour of a light at that temperature. Nothing is drawn over your screen, so screenshots and screen recordings come out in their true colours.

Windows	SetDeviceGammaRamp, for each screen on the desktop
macOS	CGSetDisplayTransferByTable, for each online display
Linux, X11	RandR's SetCrtcGamma, for each lit CRTC
Linux, wlroots on Wayland	zwlr_gamma_control_v1, for each output
Linux, GNOME on Wayland	Night Light's temperature, through gsettings
Linux, KDE on Wayland	Night Light's temperature, through kwriteconfig6

The colour of each temperature comes from Krystek's fit to the colour of a glowing black body, worked out relative to 6500 K so that daylight leaves your screen exactly as it was. Sunrise and sunset come from NOAA's sunrise equation. Your time zone comes from the OS, and its city from a table built from tzdata and CLDR (assets/make_zones.py writes src/zones.rs).

If a screen's ramp already has a calibration curve on it, Luz tints that curve rather than replacing it, and puts it back when you quit. The OS drops ramps now and then (after sleep, a resolution change or a full-screen game), so Luz sets them again every few seconds.

The sun is drawn in code (src/icon.rs). The images in assets/ and docs/img/ are generated from it with .\build.ps1 -Icons. The glyphs in the menu come from Lucide (ISC): assets/icons/make.sh rasterises them into assets/icons/glyph/, and assets/icons/LICENSES.md has the license.

Configuration

%APPDATA%\Luz\config.json on Windows, ~/Library/Application Support/Luz/config.json on macOS, ~/.config/luz/config.json on Linux. You can do everything from the menu, but you can edit the file if you'd rather. Luz notices changes within a second, so there's no need to restart it.

{
  "dayKelvin": 6500,
  "sunsetKelvin": 3400,
  "bedtimeKelvin": 1900,
  "bedtime": true,
  "bedtimeAt": "23:00",
  "wakeAt": "07:00",
  "fadeSeconds": 3600,
  "latitude": null,
  "longitude": null,
  "hotkeys": true,
  "pausedUntil": 0
}

Key
dayKelvin, sunsetKelvin, bedtimeKelvin	Any temperature from 1200 to 6500, not just the ones in the menu.
bedtimeAt, wakeAt	24-hour clock, local time. Any minute, not just the menu's half hours.
fadeSeconds	How long each fade takes. 1 second to 3 hours.
latitude, longitude	Degrees, south and west negative. Both or neither; null guesses from the time zone.
pausedUntil	A Unix time. Luz keeps a pause going across a restart.

Troubleshooting

Luz writes a log to luz.log, next to the config. It notes where it thinks you are, the day's sunrise and sunset, every change of phase, and anything the OS refused:

INFO  location: Bangkok, from your time zone
INFO  sun for 2026-10-23: up 06:10, down 17:55
INFO  2 screen(s) tinted
INFO  now Evening
INFO  2 screen(s) tinted, held at about 2940 K by Windows

luz status prints the same picture from a terminal.

Windows stops at about 3000 K

Windows refuses gamma ramps that stray too far from a straight line, and on most screens that limit falls somewhere around 3000 K, short of the Candle colour Bedtime mode uses. When that happens Luz goes as warm as Windows allows, and the menu says Windows is holding it at about 2900 K.

The installer lifts the limit (it's the Allow colours warmer than Windows' usual limit box, ticked by default). With the portable copy, click Allow warmer colours… in the menu and say yes to the admin prompt. Either way, Windows only reads the setting when it starts, so restart once. It's the same setting f.lux uses (GdiIcmGammaRange under HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ICM), and it only allows warmer colours. It doesn't set any.

A monitor isn't under Brightness. It doesn't answer DDC/CI. Look for a DDC/CI setting in its on-screen menu, and try it on a direct cable rather than through a dock or adapter.

One screen isn't changing. Windows skips the gamma ramp on screens in HDR mode. Turn HDR off for that screen in Settings > Display. Some DisplayLink and other USB displays have no ramp at all.

The colour flickers. Something else is setting it too, usually f.lux, a monitor vendor's app or a game's own gamma setting. Quit the other one.

The sunset time is wrong. Check Settings > Location. If it says a city that isn't near you, give Luz your coordinates with luz location.

My screen stayed orange after a crash. Run luz reset, or start Luz again. On macOS the OS puts the colours back by itself when Luz quits, even if it crashed.

Opening Luz again doesn't seem to do anything. It did. The second copy paused or resumed the running one, then quit. Check the sun.

Build

winget install Rustlang.Rustup
choco install innosetup -y     # only for the installer

.\build.ps1                    # tests + release binary + installer, in dist\
.\build.ps1 -Run               # ...then launch it
.\build.ps1 -Choco             # ...plus the Chocolatey package
.\build.ps1 -Icons             # regenerate assets\icon.ico and the PNGs
.\build.ps1 -SkipInstaller     # binary only

./build.sh                     # tests + release binary + dist/Luz.app
./build.sh --run               # ...then launch it in the menu bar
./build.sh --universal --dmg   # what a release ships: arm64 + x86_64, in a .dmg

On Linux, with the GTK and AppIndicator headers:

sudo apt install libgtk-3-dev libxdo-dev libayatana-appindicator3-dev
cargo build --release          # target/release/luz

All you need is the Rust toolchain. The schedule, the colours, the sun and the menu are shared. Only the OS-specific parts are split: GDI vs CoreGraphics vs RandR vs wlroots ramps (or GNOME's or KDE's Night Light), the Windows time zone name vs /etc/localtime, and WinRT toasts vs osascript vs notify-send. Monitor brightness (src/backlight.rs) is Windows only for now, through the Monitor Configuration API.

cargo test covers everything that doesn't need a desktop: sunrise and sunset against NOAA's full calculator, the schedule through a day with and without Bedtime mode (and in a polar summer), the colour of each temperature, time zone lookups, config parsing and the icon drawing. Three tests that touch the real screens (two tint them for a moment, one steps a monitor's brightness down and back) are left out by default; cargo test -- --ignored runs them.

The landing page is docs/index.html, a single static file served by GitHub Pages from /docs.

Releasing

1. Bump version in Cargo.toml and add a section to CHANGELOG.md.
2. git tag vX.Y.Z && git push origin vX.Y.Z

The release workflow builds the DMG on macOS, the installer and portable exe on Windows and a tarball on Linux, puts them on a GitHub Release with checksums, and updates the Chocolatey and winget manifests with the new version and checksums:

• Chocolatey is pushed automatically when the CHOCO_API_KEY secret is set.
• winget: submit the manifest-winget artifact to microsoft/winget-pkgs, or use wingetcreate submit.
• Homebrew: kidchenko/homebrew-tap bumps Casks/luz.rb itself, right away when the HOMEBREW_TAP_TOKEN secret is set and otherwise on its daily run.

If you run the workflow by hand from the Actions tab, it's a dry run. It builds everything and uploads it as artifacts, but doesn't publish anything.

Not yet

• Monitor brightness on macOS. It needs the private services MonitorControl and Lunar use; for now Dimmer and Brighter darken the picture there.
• Other Wayland desktops. COSMIC, for one, has no way in yet.
• Linux packages. A .deb, an AUR package or a Flatpak, rather than a tarball.
• Brightness on the schedule. Dimming at sunset along with the colour.
• Pause for an app. Off while a photo editor or a game is in front, as f.lux does.
• A signed, notarized Mac build. No more Gatekeeper step, and notifications would show up as Luz.
• Code signing on Windows. No more SmartScreen warning.

License

MIT. The menu's glyphs are from Lucide (ISC); see assets/icons/LICENSES.md.