Abendrot app icon - a golden sun setting into a calm sea beneath a warm twilight sky.

Abendrot

A macOS app for your circadian rhythm

Abendrot warms your entire workspace - including the Studio Displays and external panels where Night Shift stops. Open source, zero telemetry, grounded in melanopic research.

Download for macOS GitHub Blog
Your screen is warmed to 2500 K right now. Press & hold - or hold the space bar - to lift the warmth to true color.
The science below

The gap

Most warming tools quietly give up on half your desk.

Night Shift and f.lux do a fine job on a MacBook's built-in panel. Step beyond it and the coverage thins out - exactly where a lot of focused evening work happens.

Buttonless Apple displays

Studio Display, Pro Display XDR and similar panels expose no manual controls - and built-in night modes don't reach them, so they stay cool while everything else warms.

External monitors

LG UltraFine and other third-party displays often sit outside the reach of the system warming you trust on the laptop screen.

The newest Apple silicon

On the latest hardware, some long-standing warming paths fall back or stop entirely, quietly leaving displays at full daytime blue.

One mismatched desk

The result is a split workspace: a warm laptop next to a cold external - the jarring seam Abendrot is built to close.

How it compares

Deeper warmth, on every display.

Apple’s Night Shift is a fine, free, built-in option - especially on a MacBook’s own screen. Here’s where Abendrot goes further.

Warmest setting

Night Shift

~2700–3400 K1 - Apple publishes no value; never reaches ~1900 K

Abendrot

~1900 K - the warming curve takes the blue channel to its practical minimum

Blue at the warmest setting

Night Shift

Reduced, but not eliminated2

Abendrot

Driven to its practical zero

External & buttonless Apple displays

Night Shift

Works on Apple’s own (Studio Display, Pro Display XDR); inconsistent on third-party monitors1

Abendrot

Warms every display - built-in and external - via its gamma, DDC, and overlay engine

What you see

Night Shift

A “Less Warm / More Warm” slider

Abendrot

The actual color temperature and warming method, shown per display

Open & private

Night Shift

Closed-source; Apple’s telemetry

Abendrot

Open source (MIT), zero telemetry by default

Night Shift is free, built into macOS, and great for set-it-and-forget-it use on the built-in display. Abendrot is for people who want deeper warmth and reliable warming across every external display.

  • Apple publishes no Kelvin value for Night Shift; ~2700–3400 K is a third-party estimate. On external displays, Apple states performance “depends on the characteristics of the display”.
  • Per f.lux co-founder Michael Herf (2017 spectrometer measurement), Night Shift removes under ~30% of blue light’s biological impact at its default setting.

The engine

One warming layer for every panel, chosen per display.

Abendrot reaches each display with the strongest method it supports, and shows you which one it used. No display is left at full blue because of a missing button.

Universal

Gamma - the true-warm path

An OS-level color transform that warms every display, built-in and external, by reshaping the output curve. This is the universal foundation - it works where manual buttons don't exist.

Opt-in

DDC - a hardware upgrade

When a monitor speaks DDC/CI, Abendrot can warm the panel in hardware as an opt-in step - a deeper adjustment on supported external displays.

Floor

Metal overlay - the safety floor

Where neither applies, a lightweight rendered overlay keeps the warmth visually consistent - so the whole desk stays in step.

The warming curve runs 6500 K → 1900 K. At its warmest everyday setting, the curve takes the display's blue channel to zero - a property of the blackbody-based curve itself, not a measured per-panel emission figure.
6500 K · daylight 1900 K · blue → 0

The science

Lower melanopic load, in the band the body clock reads.

The body clock isn't tuned to brightness or to a color's name - it's tuned to a narrow band of short-wavelength light. Here's what the research actually says, and where to read it.

warming removes this first peak ≈ 490 nm 400 490 530 600 700 nm
Illustrative - the CIE S 026:2018 melanopic action spectrum, not a measured output of Abendrot. It shows where the melanopsin system is most sensitive (peak ≈ 490 nm) and how that sensitivity falls toward the red. Warming attenuates the short-wavelength region on the left first.
  1. 1

    The melanopsin-containing ipRGCs that set the circadian clock are most sensitive to blue light around 480–490 nm.12 That is the band screen warming attenuates first.4

  2. 2

    In a controlled human display study, it was the melanopic content of evening screen light - independent of luminance and color appearance - that drove the effect on melatonin and time to fall asleep.5

  3. 3

    Expert consensus states concrete evening light targets in melanopic EDI, not in Kelvin - keeping evening melanopic EDI low, starting hours before bed.6

  4. 4

    Individual sensitivity to evening light varies more than fifty-fold between people, so there is no single “right” setting - which is why Abendrot gives you a slider rather than a verdict.7

One honest note on dose: warming removes blue, but the circadian effect of light also depends on its intensity.8 For the calmest evening, remove the blue and lower your screen brightness.

Open & private

A warmth tool you can read every line of.

Trust shouldn't require faith. Abendrot is open source and collects nothing by default - the opposite of the night-mode apps that quietly phone home.

MIT

Open source

Licensed MIT. Free to use, free to fork, free to inspect - no asterisks.

0

Zero telemetry

No analytics, no tracking, no account. By default it reports nothing, to no one.

macOS

Native menu bar

A small, native menu-bar app - not a browser shell, not a daemon you can't see.

View the source on GitHub

References

  1. Berson DM, Dunn FA, Takao M (2002). Phototransduction by retinal ganglion cells that set the circadian clock. Science. doi.org/10.1126/science.1067262
  2. Brainard GC, et al. (2001). Action spectrum for melatonin regulation in humans. The Journal of Neuroscience. doi.org/10.1523/JNEUROSCI.21-16-06405.2001
  3. Thapan K, Arendt J, Skene DJ (2001). An action spectrum for melatonin suppression. The Journal of Physiology. doi.org/10.1111/j.1469-7793.2001.t01-1-00261.x
  4. CIE (2018). CIE S 026/E:2018 - System for Metrology of Optical Radiation for ipRGC-Influenced Responses to Light. CIE International Standard. doi.org/10.25039/S026.2018
  5. Schoellhorn I, et al. (2023). Melanopic irradiance defines the impact of evening display light on sleep latency, melatonin and alertness. Communications Biology. doi.org/10.1038/s42003-023-04598-4
  6. Brown TM, et al. (2022). Recommendations for daytime, evening, and nighttime indoor light exposure to best support physiology, sleep, and wakefulness in healthy adults. PLoS Biology. doi.org/10.1371/journal.pbio.3001571
  7. Phillips AJK, et al. (2019). High sensitivity and interindividual variability in the response of the human circadian system to evening light. PNAS. doi.org/10.1073/pnas.1901824116
  8. Zeitzer JM, et al. (2000). Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression. The Journal of Physiology. doi.org/10.1111/j.1469-7793.2000.00695.x