Circadian Reality

Michael Herf
3 min readOct 7, 2015

VR glasses are going to affect sleep like nothing we’ve ever seen

I took my iPhone 6 and popped it into Google Cardboard. Put the spectrometer where my eyes usually go, and pushed the button.

The meter took the reading really fast…

360 lux

f.luxometer says that’s 90% as bright as daylight — meaning it can kick your circadian clock two timezones away, after looking at a device for just a few hours. That’s almost as fast as the sun.

That measurement of Google Cardboard (not a specialized VR device at all) is more than double the 27" Apple Thunderbolt Display cranked up all the way, at a really close distance. I dim that screen like crazy at night.

So that means that Google Cardboard with an iPhone is pretty much the brightest screen we’ve ever measured. The iPhone 6 is already a really bright screen, and I never put it 2 inches away from my eye. Except that’s what you do with Cardboard.

Just for the math, that’s 36x brighter than my normal iPhone. Because the inverse-square law makes a 2" viewing distance 36x brighter than a 12" one.

A light therapy box on your face

At these brightness levels, and with a wide field-of-view, we’ll be able to shift sleep by more than two hours in just one night.

For a casual device that you might use at night, it’s sort of unprecedented. Watching a movie on a 70" screen doesn’t even compare, because you usually sit pretty far back from a screen in your living room.

With your phone in a dark room, you might dim it because it’s so much brighter than what’s around it — not so with a great pair of VR goggles, because you can see that gorgeous wide angle view with no darkness around, and you won’t feel uncomfortable at all.

The only real question is: how bright is the content you’re seeing, and can you dim the screen at the right times? In our lab, we measure screens as if everything is a white page (like Google’s homepage), but if it’s a darker game or movie, the results could be a little more reasonable.

But just think, it might keep going: in a few years, we’ll be able to dial up the power budget by a factor of 2 or 5 again, and make things even brighter.

This means that we absolutely need more software to be circadian-aware, to know if it’s right before bed, or if it’s a dreary morning in Seattle, to do the right thing at the right time.

What’s amazing is that we have devices coming up that can do so much good. If we make the devices aware of the people using them, we can improve sleep and make people happier and more alert at the right times.

But if we don’t, this new way to look at screens has the potential to steal a bunch of sleep, more than the brightest screens we’ve ever seen.



Michael Herf

co-founder of f.lux, finding the connections between circadian rhythms, sleep, healthy buildings, and light. (Previously made Picasa.)