f.lux is a reasonable first step. It shifts your screen color warmer at night and it does that fine. Circadian Shield is for people who found that was not enough — deeper dimming below what the OS allows, PWM comfort modes for flicker-sensitive users, scheduled display control across 11 modes, and 60+ display tools built around circadian science.
f.lux is free and simple to install. It has been around for over a decade and runs on Mac, Windows, and Linux. If your only need is a warmer screen after sunset, f.lux handles that adequately.
It applies an automatic color temperature shift based on time of day. For many people, that is enough. There is no setup beyond entering your location, and it stays out of your way.
If that is solving your problem, there is no reason to switch. But if you are here, you probably found that it was not.
These are specific, verifiable differences — not marketing adjectives.
Circadian Shield can dim the display below what the operating system allows. f.lux adjusts color temperature but does not extend the dimming range. If your screen still feels too bright at the lowest OS brightness setting with f.lux running, Circadian Shield solves that.
Some displays use pulse-width modulation to control brightness, which causes a subtle flicker that triggers headaches and eye strain in sensitive users. Circadian Shield includes software overlay dimming that reduces exposure to PWM flicker. f.lux does not address PWM at all.
f.lux operates on a simple preset model: warmer at night, normal during the day. Circadian Shield offers 11 distinct modes — Auto, Movie, Reading, Coding, Presentation, Gaming, Biohacker, Sunglasses, Dark, Custom, and Disabled — that can be scheduled, triggered manually, or assigned per-app.
Beyond color temperature, Circadian Shield bundles a broader toolkit: per-display profiles, screen effects, spotlight dimming, inactivity pause, and keyboard shortcuts. These are bundled in one app rather than requiring separate utilities.
Circadian Shield is built on melanopic equivalent daylight illuminance (EDI) research — the CIE S 026:2018 standard that measures the light wavelengths actually responsible for circadian disruption. f.lux uses color warmth as a proxy. For more on the difference, see the science behind Circadian Shield.
Circadian Shield includes built-in screen break reminders with flow detection and video call pausing. f.lux does not include a break timer.
| Feature | f.lux | Circadian Shield |
|---|---|---|
| Color temperature adjustment | Yes | Yes |
| Deep screen dimming (below OS minimum) | No | Yes |
| Number of display modes | Presets | 11 modes |
| PWM flicker comfort mode | No | Yes |
| Break timer (20-20-20 rule) | No | Yes |
| Melanopic EDI calibration | No | Yes (CIE S 026) |
| Mac support | Yes | Yes |
| Windows support | Yes | Yes |
| Price | Free | From $4/mo (14-day free trial) |
No. Circadian Shield starts at $4/month with a 14-day free trial that includes full Pro features. f.lux is free, but it only adjusts color temperature. Circadian Shield adds deeper dimming, PWM flicker and eye strain comfort modes, 11 display modes, a break timer, and melanopic EDI calibration.
Yes. Circadian Shield is available on both Mac and Windows.
The main differences: deeper screen dimming below the OS minimum, PWM flicker comfort modes, 11 schedulable display modes, a 20-20-20 break timer with flow detection, and calibration built on melanopic EDI research rather than color warmth alone.
For some people, yes. If a warmer screen color at night is all you need, f.lux handles that. But if you still find your screen too bright, get headaches from display flicker, or want more control over how your display behaves throughout the day, f.lux may not go far enough.
Install Circadian Shield from the download page, then disable or uninstall f.lux. Running both at the same time is not recommended — overlapping color filters can produce unpredictable results.
Yes. Your subscription covers both platforms.
14-day free trial. Full Pro features. No credit card required.