Is Circadian Shield free like f.lux?
No. Circadian Shield Pro is $47, a one-time payment that covers up to 3 computers on Mac and Windows, with free updates and a 14-day money-back guarantee. 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.
Is f.lux better than Windows Night Light?
For control, yes. f.lux offers warmer presets down to 1200K, separate daytime, sunset, and bedtime color targets, a disable-for-this-app option, and Philips Hue smart bulb control. Night Light is a single strength slider on one schedule. Night Light is the better pick if you cannot install software on the machine or just want zero setup. For a plain warmer screen at night, either one works.
Why does Windows Night Light sometimes stop working?
The usual causes are driver related. Microsoft's support documentation notes Night Light is not available on devices using DisplayLink or Basic Display drivers, and a recurring user complaint is Night Light dropping out when full-screen games or video take over the display. If the sunset-to-sunrise schedule fails, check that location services are enabled. f.lux avoids some of these problems, though any software filter still depends on the GPU driver cooperating.
Can I run f.lux and Windows Night Light at the same time?
Turn one off. Both adjust the same display color output, and stacking them produces double-filtered color that is hard to predict. Pick the tool you prefer and disable the other. The same rule applies to running either one alongside Circadian Shield.
Does f.lux control smart lights?
Yes. f.lux can control Philips Hue bulbs so your room lighting warms in step with your screen in the evening. Windows Night Light does not control smart bulbs, and neither does Circadian Shield, which focuses on the display itself.
Does f.lux block blue light?
It reduces blue light rather than blocking it. Warming the screen color shifts the display's output away from short blue wavelengths, and the warmer the setting, the larger the reduction. No software filter removes blue light entirely while the display is on. Melanopic EDI is the measure of how much a given setting actually matters for circadian timing.
Does Circadian Shield work on Windows like f.lux does?
Yes. Circadian Shield is available on both Mac and Windows, and one purchase covers up to 3 computers across both platforms.
What does Circadian Shield do that f.lux does not?
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.
Is f.lux good enough for sleep?
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.
How do I switch from f.lux to Circadian Shield?
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.
Does f.lux work on Mac?
Yes. f.lux runs on macOS 10.15 and later, supports Apple Silicon, and is a free download from justgetflux.com. It lives in the menu bar and shifts color temperature on a sunrise to sunset schedule once you set your location. Circadian Shield is built for the same Mac users who want more than a sunset color shift.
Is f.lux safe to install?
Yes. f.lux has been available since 2009, has tens of millions of users, and only needs the Accessibility permission required to adjust display color. It does not transmit usage data in any documented way. The one thing to watch is running it alongside another color tool like macOS Night Shift or True Tone, since overlapping filters can fight each other.
Who is the competitor of f.lux?
On Windows the first alternative to try is the built-in Night Light. On macOS it is Night Shift. Beyond the built-ins, the main competitors are Iris (cross-platform and paid, with blue light reduction plus break reminders) and Circadian Shield (solar-position scheduling and melanopic EDI calibration rather than color warmth alone). For a three-way breakdown, see Iris vs f.lux vs CircadianShield.
Does f.lux reduce PWM flicker?
No. f.lux adjusts your screen's color temperature and does not touch backlight PWM, the rapid on-off pulsing many displays use to dim. What can help is keeping hardware brightness high, where most panels run at or near full duty cycle with little PWM, and dimming the image with a software overlay instead. That is how Circadian Shield's PWM comfort mode works. The honest limit is that no software can remove flicker from a backlight that pulses even at 100% brightness. In that case only flicker-free hardware fixes it. See our flicker test, the PWM and headaches guide, and how to verify a flicker-free monitor.
Night Shift vs f.lux, which is better?
They overlap more than they differ. Night Shift on Mac and Night Light on Windows are built in and free, with a single warm-to-cool slider on a sunset-to-sunrise schedule. f.lux is also free and adds finer color control, more presets, and cross-platform support including Linux. If you want a bit more control than the built-in toggle, f.lux is the better free pick. If you also need deeper dimming, PWM comfort, or melanopic EDI calibration, neither goes that far, which is where Circadian Shield comes in.
What is melanopic EDI, and why does f.lux not use it?
Melanopic equivalent daylight illuminance (EDI) is the measure in the CIE S 026:2018 standard for how strongly light stimulates the melanopsin in your eyes, the signal most tied to circadian timing. f.lux and the built-in tools work in color temperature (Kelvin), which is a reasonable proxy but not the same thing. Circadian Shield calibrates its filtering to melanopic EDI directly. It is designed to support your evening wind-down rather than to treat any condition. More on the melanopic EDI explainer and the science page.