F.lux Review: the software that makes you sleep better

Here’s a little thought experiment. How many technological innovations in the last 15 years have become indispensable in your daily lives? I can think of quite a few- the mobile phone, WiFi, GPS navigation, THE INTERNET, I could go on….

Recently I added a new one to my list. A  simple piece of computer software that I would now find hard to live without.

The cult of F.lux

You’d be forgiven if you’ve never heard of F.lux. It’s freeware so you won’t have seen any advertising or marketing campaigns.

Despite being well under the radar, F.lux has a large, loyal and enthusiastic userbase, as demonstrated by the thousands of comments on the download page. But it’s not easy to describe in words why there are so many devotees like me. Like all religious cults, F.lux is an experiential process, you have to live it to truly understand…

So what does F.lux do?

The strapline for the software is “Better lighting…for your computer“. Whilst this gives you a very broad idea, many people miss the point completely. There’s a misconception that F.lux is like a software version of the ambient light sensors found on most Apple products and a lot of laptops these days.

But there’s a subtle and important distinction. Instead of adjusting the brightness, F.lux works discreetly in the background, automatically adjusting the colour temperature of your screen. It adapts your computer’s display to the current time, “warm at night and like sunlight during the day.” In effect it tries to match the light from your computer to the light in your natural environment.

I still don’t get it, why do I need F.lux?

Kelvin Scale (K) – Color Temperatures

In order to fully benefit from using F.lux, it’s useful to know a little of the science behind this app.

Visible light is made up of different wavelengths which our eyes perceive as colour. These colours can be represented on a ‘temperature’ scale, measured in Kelvin(K). As the day progresses, the colour temperature changes – think of the difference between a bright clear morning and a golden sunset.

Human beings have evolved alongside these daily light patterns, developing biological mechanisms to trigger sleep and wakefulness. When the light starts to fade at night, our bodies start producing melatonin, aka the ‘sleepy hormone’.

As morning approaches, the daylight becomes a signal to stop producing melatonin, which makes us feel alert and awake. It’s a beautifully balanced symbiotic relationship with nature. The problem is, a 21st century lifestyle doesn’t always treat this relationship with a lot of respect.

Using computers at night wrecks your sleep

Computer screens – and that includes smartphones and tablets – emit light in the blue part of the spectrum. This doesn’t cause any issues in the daytime, but at night, this blue light limits the production of melatonin. In layman’s term, the bright light from your laptop/iPhone/iPad etc screws up your sleep-wake cycle.

If you want to know more about the science, the developers have provided a great resource on the site here.

F.lux settings

F.lux Preferences Settings Mac
F.lux Settings (an old version… on a Mac…)

F.lux is designed to work unobtrusively in the background. Apart from the settings page, there are no controls or interfaces – the idea is you set it up once and never touch it again. The app is cross-platform (with the exception of Android devices at the moment) so there are versions for Windows, Macs, Linux and iOS.

To set it up, the first thing you need to do is add your location, then the app calculates the time of sunset and sunrise wherever you are.

Next you select what type of light you want your screen to replicate at night. You can select Tungsten, Fluorescent, Halogen or choose your own custom value by adjusting the temperature sliders.

That’s pretty much it. You can choose either a slow or fast transition between the day and night settings. I prefer slow, as you barely notice when the change happens.

F.lux in use

During the daytime you won’t notice any difference to your screen, unless you prefer to change the default daylight setting of 6500K. As dusk approaches however, your screen gradually (if you have selected the slow setting) changes to a warmer, easier on the eye, colour setting.

The first time I tried F.lux, it just seemed to me that the screen was a little more ‘red’. It took a day or two to adjust to this new hue, but now the app is on 24/7 and I would find it almost unimagineable to go back to my pre- F.lux display settings. I can’t really put it into words, but the effect of disabling F.lux at night is not unlike staring at the sun.

If you need to do any colour sensitive work like photo-editing, you can temporarily bypass the app.


So hopefully you can now you can see why I’m such a fan of this app. In summary F.lux can:

  • reduce eye strain when using your computer, or tablet at night
  • increase your productivity by letting you work later into the nightschedules
  • reduce stimulated wakefulness by minimising the effect of ‘blue light’ messing up your sleep schedule

As I mentioned earlier, F.lux is a bit of a strange concept to get your head around, you just have to see for yourself what a difference this app makes.  I’d find it very hard to use my computer at night without F.lux now. If you’re still skeptical, give it a try, it’s free so you’ve nothing to lose. You may be pleasantly surprised…

Download F.lux: It’s Free!

Image via Flickr

24 thoughts on “F.lux Review: the software that makes you sleep better”

  1. F.lux is an AMAZING program that I think **EVERYONE** should try!
    I mean it’s FREE, just install it, set your location CORRECTLY, meaning somewhere within at least 25 miles of you, and set the transition speed to slow.

    Use the program for AT LEAST 3 days and figure out if you like it by a week or two
    If not, exit the program and remove it. That simple

  2. It’s incredible how wonderful this program is!!! I can’t live without it haha

  3. Just discovered this from a friend at work, and 2 hours after use, and HOLY CRAP!! This is amazing!!!

  4. Hi drobi,
    I’m running 10.7.4. I had a few problems recently but after I updated to the latest F.lux everything seems fine now!

  5. It’s simply fantastic. It can really change how you feel when sitting at your computer.

  6. Ive been using this on my PC and ipad for a good while now and it makes such a big difference. Due to an ios upgrade my ipad isnt jailbroken anymore and ive lost f.lux – working at night without it is terrible! f.lux is truly an essential app.

  7. I normally don’t bother to leave reviews, but this program is worth the attention.
    What a big difference such a small program can make 🙂
    The only thing that would make it even better would be a ‘dimmer mode’ button that halves the light intensity of your screen. It could be used when you’re sitting in a dark room just before going to bed or right after waking up.
    Thanks Guys!

  8. My Flux is installed on Apple OX 9.3 – ‘Mavericks.’ When Flux changes the lighting, the new light colour just blinks on intervals of approx. 1second. Not at all pleasing. Am I doing something wrong?

  9. It has hotkeys for brightness control – Alt/Page Up and Down respectively.

  10. Hi Will,

    I’m a Mac user too but I’m way behind on 10.7.5 so can’t comment on Mavericks. In my experience, bug fixes have been sorted pretty quickly, so if you’re running the latest version and stilll having problems, I’d get in touch at their support page https://justgetflux.com/faq.html

  11. I sometimes need to do editing work at night. Flux makes that very difficult, as I can’t see the screen well. I’m using an iMac with OS 10.6.8. I’ve been trying to say “No” when I boot up and it asks if Flux can use the machine. It makes no difference, it still gets dark. I’ve tried to delete Flux from the computer, but it always gives me an error message saying Flux can’t be deleted because it’s open. Apparently there’s no way to close it! Any advice?

  12. You can stop F.lux loading at startup by removing the application from your login items, which you will find in System Preferences, under Users.
    However, before you do that, I’d recommend downloading the latest version, which has loads of new features, including support for people like yourself who wish to work through the night!

  13. I assume F.luxes darkroom mode is the best solution for our eyes during night time, or am I wrong?

    When switching from darkroom to normal mode in the middle of the night you can feel the light burning in your eyes.

  14. Dark Room mode is for use in photo developing rooms as it will not interfere with the film development.

  15. Doesn’t work. Screen flickers even after driver updates. No help through support or tweets…. Super bummed as I watch ALOT of Netflix at night on my computer before I fall asleep 🙁

  16. Sorry to hear you’re having issues. The app has been pretty solid for me, I’ve only ever had one minor issue in over 2 years. Support is usually pretty good, but remember this is a free app and it takes up a lot of time to answer support emails.

    Keep on persevering, it will be worth it when you get it working!

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