Glenn Fleishman, in an article at Macworld titled iOS 9.3: The new Night Shift feature probably won’t help you sleep better:

In fact, this feature likely will have little or no effect on most people. Apple hasn’t misrepresented any of the science, but clinical work done to date doesn’t point a finger right at mobile devices or even larger displays. Night Shift also can’t remove enough blue to make a difference if that color is the culprit. And blue light may not be the trigger it’s been identified as. While researchers haven’t tested the new feature yet, several factors add up to at best a placebo effect and a reminder to power yourself down.

The article is well worth a read. I just want to report my experience on the matter, an experience that leads me to believe that tools like f.lux and the Night Shift feature in iOS 9.3 can, in fact, be effective. All I can offer is anecdotal data, but I don’t think the benefits I’ve noticed are simply the result of a placebo effect.

I’ll talk about f.lux, because none of my iOS devices supports Night Shift — both my iPad 3 and iPhone 5, despite running iOS 9.3, are 32-bit devices.

I first installed f.lux on my MacBook Pro in late 2009. It came as a trusted recommendation from a night owl friend who told me he had started noticing much less eye strain immediately after trying the software. I was sceptical at first, but figured it wouldn’t hurt to give it a try. 

Now, this is probably going to sound like a sponsored testimonial, but hear me out. 

Since I started freelancing around 2000, my daily schedule and habits have been severely disrupted. Before, when I had to go to university or to a workplace by 8:30 in the morning, I typically went to sleep at 11 PM to wake up at 6:30–7 AM, more or less. As soon as the reason to wake early in the morning went away, and the freelancing demanded I stayed an increasing number of hours at my computer every day, I quickly turned into a night owl. I went through a terrible period of overwork, staying up until 5 AM to get up at 9:30 and go on with my work assignments. Since I’ve always worked with text, that means staring at words on a white electronic page for hours, and well into the night. You can imagine the effect on my eyes, eyesight and sleep. There were periods where the fatigue reached such a point that I started wearing sunglasses when working at my Mac at night. 

As for sleep, the problem wasn’t insomnia — I never had issues at falling asleep, thank goodness. In fact, I often go to bed so tired that it takes me like two minutes to fall asleep once I’ve acquired my ‘sleeping position’. The problem, before switching to f.lux, was the quality of my sleep. Sometimes my sleep got fragmented by waking up three or four times during the night (well, morning); sometimes, despite going to bed extremely tired, I would wake up after three hours and couldn’t get back to sleep no matter how hard I tried; sometimes, despite sleeping seven-eight hours, I would get up the following morning feeling more tired and unfocussed than the day before. 

You’re free to believe what you want, but after one week of using f.lux on my Mac, the eye strain was completely gone. My eyes stopped ending up bleary and teary at night, but most importantly my sleep got better too, generally speaking. I still experience the occasional bad night, but that usually happens when I sleep less than six hours. All those sleep disruptions mentioned in the previous paragraph have rapidly vanished since I started using f.lux.

Now, you might wonder: Are you sure it’s thanks to f.lux that you’re feeling better at night?

I’m quite sure, because a few months ago I did a little experiment: I disabled f.lux for two weeks. The eye strain returned almost instantly, and the quality of sleep started deteriorating from the second night on. Going back to f.lux was a relief. I know, perhaps it’s all auto-suggestion. Perhaps a more scientific way to conduct my test was to stop using f.lux for a longer period and see whether my sleep re-adjusted in the long run after the initial ‘shock’. But that second week without f.lux was hard: I had forgotten how bad reading and writing at 4 AM was. I experienced a similar drop in quality of sleep and increase in eye strain when I tried using my iPad as primary machine, and that happened before I could sideload f.lux on my iPhone and iPad. Sure, the fatigue and general disruption weren’t that severe — a 9.7‑inch display without f.lux isn’t as dazzling as a 24-inch widescreen monitor at 4 in the morning, but still, the negative effects were perceptible.

I am well aware that this is just my experience, and not scientific research. It could all just be a placebo effect for all I know, although it’s strange how my eyes get sore and teary every time I don’t use f.lux — e.g. when I happen to do some photo editing late at night, and I keep f.lux off for obvious reasons — while they remain well-rested when f.lux is enabled and I’m writing at 5 AM. And I don’t think that quality of sleep is something I can subconsciously control, so there must be some external factor to take into account for my much improved sleep these past years. Maybe the use of f.lux has just been coincidental, but what matters to me is the outcome — a better sleep.