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F.lux beta can now estimate the circadian effect of your screen brightness

The f.lux beta for Windows is making it even easier to judge the impact of your screen brightness on your body with its latest update. Version 4.21 introduces a couple of new features that not only show you an approximation of how much light your seeing, but also how it's impacting your body and circadian rhythm.

f.lux % daylight

From the f.lux release notes:

In this new build, we've exposed one of our models of how the light from screens affects your body (based on your screens' sizes, and using our 5,000-person survey to approximate your viewing distance). As you adjust settings in f.lux now (or even as you change your laptop's backlight, which is important), you'll see one of five common-sense scores for how much light you're seeing:

  • Bright as Day
  • Ready to Work
  • Staying up Later
  • Winding Down
  • Circadian Darkness

In addition, f.lux says you'll now see a measure of how much light your seeing measured as "% daylight." The preferences menu will also now tell you how light is offsetting your circadian rhythm based on time of day, indicating whether the light you're seeing is "advancing" or "delaying" your internal clock depending on time of day.

Here's a look at some of the other changes in f.lux version 4.21:

  • Notifications are redesigned, when you use the hotkeys (alt-pgup, alt-end, etc)
  • Some extra support for wide color ranges on Windows 7
  • Gaming mode (safe mode) is removed, because we've incorporated everything it does, finally. Use "very fast" transitions if you notice problems
  • We now ask for the "earliest" time you wake up, to clarify what you should do when you have a variable schedule

All of this is in addition to a new bedtime feature f.lux introduced in its previous beta release. When combined, both updates should make it easier to get some insight into how those work sessions in the wee hours of the morning are impacting your quality of sleep.

To check out the latest beta release, you can give it a download at the f.lux forums.

Dan Thorp-Lancaster is the Editor in Chief for Windows Central. He began working with Windows Central as a news writer in 2014 and is obsessed with tech of all sorts. You can follow Dan on Twitter @DthorpL and Instagram @heyitsdtl. Got a hot tip? Send it to daniel.thorp-lancaster@futurenet.com.

18 Comments
  • Sure, Windows 10 has Night Light, which is great, but F.lux is for power users ;) Love it.
  • Yes used f.lux for years, it's great.
  • Hmm, I have used it for many years, but lately it's been pretty buggy. I prefer OS level integration and Night Light (and Night Shift..yes, I use both platforms) are perfect for me.
  • Flux is a fantastic application, only started using it recently, it's definitely helping with my constant eyestrain
  • I used to use F.lux, but it interferes with software gamma settings which I had to increase for my new monitor. It doesn't have gamma options in its settings menu.
  • What do you mean interferes? I have been having problems with my Gamma settings in which it will never change. I even changed the default. 
  • It sets my settings back to the default Windows settings whenever F.lux is running, even if it's not dark outside. Even if I try to change the gamma level with the Windows color calibration tool, F.lux will force it back to the color temperature it's set to be at at the time.
  • As I said, they're trying to stay relevant 😝
  • That's not trying, but doing.
  • I hope MS introduces a Xbox night light - would be a dream to have a whole house blue light appropriate experience.
  • I'm sorry, but I just don't buy into any of this.  Yes, I understand circadian rhythm.  But the sleep we get is the sleep we choose to get.  Either we have behaviours that are generally conducive to proper rest or we don't.  If we're foolish enough to be sitting at a screen earlier or later than we should, then be prepared to accept the consequences.  I have lived my entire life hovering right around 4 hours of sleep each night.  Once in a while, if I have had a particularly physical day, my body demands I catch up on a weekend, but I am fully accustomed to this routine.  My wife absolutely requires 8 hours, in stark contrast.  But I refuse put myself through an even greater challenge of seeing a screen (which Windows 10 already continues to make this a pain with wireframe icons, etc.) by intentionally dimming or discoloring it in a misguided attempt to "trick" my body.  
  • You are missing the point. It's being exposed to blue light that has been scientifically proven to impact the amount of melatonin our body produces. Science. Can you still sleep when exposed to light? Yes, but studies find it impacts quality and how long you are in REM. As you indicate, all people are different. The basic premise is humans are biologically programmed to respond to blue light since the ONLY natural source occurs during the day from the sky. From the perspective of thousands of years of human history, it's only been within the last 10 years that this fundamentally changed for humanity. Even traditional light bulbs don't even emit much blue light. Now you are correct, that nobody understands the exact impact on your circadian rhythm, but impact to melatonin production has been proven.
  • I don't care about whatever science may be attributed to it. All I know is I prefer not to have a cold blue display shining in my eyes in the dark. All you need to do is use Night Light (or f.lux or whatever) in the dark for a while. Then flip it off. It's shocking and not in a good way. YMMV.
  • Been using f.lux for years.  Nice to see Win10 add this feature, but it's no f.lux, will stick with it, plus it does so much more!
  • Gosh, i hope f.lux comes to W10M someday...
  • I did love f.lux but have recently switch over to the nightlight feature which works as well.
  • I tried it for a month. Really does nothing for me but make my beautiful screen look like crap.
  • .