Why can't I set the time I want to go to sleep, instead of the time to wake up?



  • I don't understand why you ask me to set the time I want to wake up instead of the time I want to go to bed. By doing it the way you do, you have to make assumptions about how long I plan to sleep in order to calculate when to start warming the display. Given that people sleep for different lengths of time, it seems that it would make more sense to have people set their bedtime, rather than their wakeup time.


  • f.lux team

    We didn't know how to explain this at all in the UI, but here goes:

    If you have the lights in your house turned up really bright, and you turn them off right before you go to bed, your body takes nearly an hour to stop reacting to the light you were seeing. And the tricky part of this is--the lights you were seeing right before bed made you stay up later. So timing like this is a tricky problem.

    In nature, we have a few hours of "dim light" before we go to sleep, but of course nobody wants "darkness" when the sun sets (otherwise why would we have artificial lighting at all?). Our goal with f.lux is to find a balance that can achieve "most" of the benefits of artificial lighting while getting you wound down to feel tired when you go to bed.

    We think it's ideal to have an environment where your body can produce "most" of its natural melatonin on its natural schedule. This isn't a signal that says you have to go to bed right away, but where the light isn't having a big effect on keeping you up even later.

    If you Google around for it, you'll see that people have a melatonin rhythm that is quite a bit greater than the time they're asleep--so in natural conditions (especially in the winter) there is time spent awake, even in the dark.

    One theory about using wake time as a circadian marker is that the cortisol rhythm is connected to the circadian clock and so it "wakes you up" at a predictable time, but there is a lot of variation in this, so it is only an approximation.

    We can go into any level of detail about it, but it is very hard to do this in the UI, which is why we chose the wake time as the best question we can easily ask, and try to tune all the rest of the timing for you.

    We're going to add more customization as we figure out more about how this affects people, but it will be in the context of sleep timing and circadian rhythm, so it probably won't be "just pick a time you want to turn out the lights".


  • f.lux team

    f.lux dims the screen around the time when your body should start making melatonin. That cycle takes about 10 hours to complete. We use wake time because it's a nice way to synchronize your timing, and you'll feel crummy if you wake up before your body completes its melatonin cycle (https://justgetflux.com/news/2014/12/22/study.html).

    We don't know when you'll feel tired, we just want you to notice when you feel tired. Whenever you're ready, you decide to go to bed.



  • I really appreciate your effort to make it as "natural" as possible, and I get you rationale about it. However, it leads to a bit of a problem for me. I really like the idea of flux, since I am starting to suspect that the light from my laptop delays the onset of sleep, but being able to set some sort of a time frame instead of just basing it on location would be pretty awesome for me.

    Why? Because I live in the very Northern part of Sweden, which means that I have about 3½ hours of daylight each day right now, and with the sun setting at about 13.30 (or 1.30 PM) this time of the year, I'm not sure it's really necessary for my body to start producing melatonin that early.. :)

    I'd love to be able to set it to start dimming the lights at like ~21.00, and then going to sleep at ~23.00, waking up at ~7.00 or something. I have not read enough about melatonin cycles, but if it's accurate that it takes 10 hours for it to complete, the current settings based on my location would mean that it'd finish at 23.30.

    Anyway, as I said, I get your thinking behind it, and I'm sure that this isn't much of a problem for the vast majority of your users, but for the few of us living in subarctic regions, it gets a bit impractical.. :)



  • ..and now I realized that I posted in the osx part of the forum, which wasn't my intention. I apologize. I use the PC version, and have not found a way to set even wake up time yet, just based on my location.. Anyway, my bad, sorry.


  • f.lux team

    @anticute we owe Windows a very big update with the newer circadian features! We think a lot about the people in your part of the world, it's an interesting (and somewhat tricky!) problem.



  • Thanks for the reply, and for being cool with the foibles of a new user!

    Yeah, it's a bit tricky in general, this thing with the day/night cycle. In the middle of the summer, on the other hand, we don't have sunsets at all for a couple of weeks.. :)

    Takes a bit of getting used to, but honestly it's easier to live with 24h of light than the other way around (if it's bothering you there are always blinds), at least people don't have to fight SAD and vitamin D deficiency to the same extent..

    Anyway, good to know, and I'm definitely looking forward to having that feature in the future!



  • Probably most people get up at a regular time to go to their jobs or their kids, and have more flexibility about when they go to bed. F.lux doesn't tell you "you must go to bed now". It assumes you'll try to go to bed in time to get about eight hours of sleep. But that doesn't necessarily work for everyone.

    On the Mac you can easily set the time you want to go to bed by simply adding eight hours to it, and setting it as the time you wake up. It doesn't really matter if you don't actually wake up at that time, except that if you sleep less than eight hours and want to use the computer when you get up, you may have to use "disable for an hour". Eventually we might get the option for f.lux to disable itself at sunrise rather than at wake time, or at something other than eight hours after bedtime.

    You might find the notifications of "you're waking up in eight hours" confusing if you don't sleep eight hours, or you don't always wake up at the same time. I disabled the Backwards Alarm Clock in Options, and use a different app that notifies me when it's getting time for bed. I find sticking to a fairly strict bedtime is best - and f.lux has been very helpful with that - and then I sleep as long as I can, which is almost never eight hours.

    Even on the Mac, the Sunset time can be difficult for people in the North. It's been interesting for me to learn the names of all the cities closer to the Equator and a couple of hours west of me, in order to get my Sunset colour to kick in at a reasonable time :-) Again we may get a simpler option for it in the future, but for now that works reasonably well.


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