Flux display: what f.lux is and how it works

What f.lux is

f.lux is software that makes the colour of your computer screen follow the time of day. Its home page says it adapts the display to the time: warm at night, like sunlight in the day.

When people search for a "flux display", this is the app they mean. It is free on macOS and Linux, and free for personal use on Windows. The site also sells a corporate edition and asks for donations.

How f.lux works on a Mac

You download it from justgetflux.com and open it. Then you tell it two things: what kind of lighting you have, and where you live. From your location it works out when the sun sets, and it changes the screen colour on its own from there.

So there is a little setup. You pick the lighting type that fits your room, and that sets the evening colour you get.

What f.lux doesn't do

f.lux changes colour temperature. That is the mix of blue and red on the screen. It does not change brightness. If your screen is too bright at night, you still turn the brightness down yourself.

It also depends on what you tell it. The lighting type and location you enter decide the colour you get, so a wrong answer gives a wrong result.

Common mistakes

• Expecting it to dim the screen. It only changes colour.
• Leaving it on for work where colour must be exact, such as photo editing. A warm screen shows colours differently.
• Entering the wrong location. The sunset time comes from where you say you are.
• Judging it in daylight. The change shows up in the evening, not at noon.

A simpler option for the Mac

I made Lumiv, a free menu bar app for the Mac. I wanted my screen to follow the sun without me setting anything.

It finds your location and works out your local sunrise and sunset. In the day it sets the screen to 5000K (Health mode). At night it turns the screen deep red and removes blue light (Sleep mode). The names are labels for the two modes, nothing more. It works on every connected display at once, and it comes back after your Mac wakes or unlocks.

Lumiv has limits. It is Mac only and needs macOS 14.6 or later, so it is no help on Windows or Linux. It has nothing to tune: no lighting type, no sliders. If you want to tune the colour to your room, f.lux gives you more control. It changes colour only, never brightness. Your location never leaves your Mac, and there is no account and no tracking.

Get it from the Mac App Store. It is free, with no ads and no subscription. For the built-in option, read how to make your Mac screen warmer at night. For a side-by-side, see Lumiv vs f.lux.

Questions

What is flux?

Flux usually means f.lux, a free app that changes your screen colour to match the time of day. It is warm at night and like daylight in the day. It changes colour, not brightness. You can get it from justgetflux.com for macOS, Windows or Linux.

What is flux for computers?

It is a small program that runs in the background on a computer. You give it your location and lighting type, and it changes the colour of the whole screen as the day goes on. You don't open it each evening. It does the change by itself once it is set up.

Is the flux app free?

Yes, on a Mac. The f.lux site lists macOS as free, Linux as free, and Windows as free for personal use. It also offers a corporate edition and asks for optional donations. Lumiv, the app I made, is also free in the Mac App Store.

How do I turn off f.lux?

To stop it for good, quit the app and drag it from your Applications folder to the Trash. Your screen then goes back to its normal colours. If you only want a pause, check the app's own menu for the option.

Does flux change screen brightness?

No. It changes the colour temperature, which is the balance of blue and red on the screen. Brightness stays where you set it. Use the brightness keys on your Mac if the screen is too bright.