Imagine it’s summer, and you live way up north. The sun is up for 22 hours of the day. Sunlight is good for sleep, right? Your sleep must be great.
Except, no. It sucks. And the reason it sucks isn’t just because it’s hard to sleep when it’s bright outside (people in northern latitudes know about blackout curtains). It sucks because sleep is a rhythm, and sleep suffers when your light exposure isn’t rhythmic enough.
Said another way: There are times of the day when you want light—a bunch of it!—for good sleep. But there are also times when light is actively bad for sleep.
This isn’t an easy concept to get. People are hardwired to understand “more of good thing” → “better” and “more of bad thing” → “worse.” We’re less adept at reasoning about things where the way you get more of the good thing is by being more rhythmic.
My eternal analogy is that sleep is like being on a swing.
Light exposure is like a push in the outward direction.
It’s good to get pushed forward when you’re heading forward.
It’s bad to get pushed forward when you’re heading backwards.
Light’s the same way. If you had 22 hours of daylight available to you, there would be times where that light was good for your sleep (morning, during the midday), and times where it was actively screwing your sleep up (late in the day, middle of the night). And this isn’t just true of sleep. The same applies for all the circadian rhythms in your body, which control metabolism, immune strength, DNA repair, hormones, you name it.
“Hang on,” you say. “I see where this is heading. You’re going to tell me that late daylight in the summer on Daylight Saving Time (DST) is screwing my sleep up, and that’s why we should switch to permanent Standard Time (ST). Except that’s stupid, because we’ve had DST in the summer for decades, and everything has been totally fine.”
You got me. Would sleep and health be better on Standard Time in the summer? Yep, 100%. Have late sunsets and DST in the summer caused the world to end? Of course not. This is one of the reasons why many sleep/circadian people have their order of preference for time systems as:
- (best) Permanent Standard Time.
- Current system where we do Standard Time in the winter and DST in the summer
- (way, way down) Permanent Daylight Saving Time.
Even though I’m not a fan of it, we’ve gotten by on summer DST for a long, long time. And people live at these super northern latitudes! They’re not collapsing the second they get a 22.1 hour day and gasping out, “it… was the light… that did it…. (eyes turn to cartoon Xs)” in their final moments.
But adopting DST in the winter is a really bad idea. There are good safety arguments to be made, but as a circadian mathematician, I think of it this way: on permanent DST in the winter, you have very weak light at the times you’d want it, given when society is making you have to get up…
…and too much light later in the day, when light’s having the opposite effect on your body.
You’d be more robust to that later-in-the-day light if you had morning light to counteract it. But on winter DST, the sun’s just not there when society’s making you wake up and start your day. This imbalance messes up your sleep rhythm (and all the other rhythms in your body as well).
So, in conclusion: Am I sympathetic to people wanting more light during the fun parts of the day? Absolutely I am. But we’re on the cusp of making a policy decision that puts us on either permanent ST or permanent DST. Do we really need to relearn the lessons of all the times permanent DST has failed before, or can we skip that part, and go to the system that Arizona’s had since 1968? Permanent Standard Time, thanks.
