Let’s start with a couple obvious things. If you lived in a bunker, and you never ever saw the sun, the choice between permanent Daylight Saving Time and permanent Standard Time would really not matter to you. We could just pick one and roll with it, and you would continue to be a person who lives in a bunker and sets their lighting to whatever they want, whenever they want it.
Choosing between permanent DST (pDST) and permanent Standard Time (ST), then, is choosing where you want the sun to be, relative to all the things on your calendar you have to be awake for. The sun matters because it’s way brighter than all the lights you’ve got in your house, and it’s free, and it lights all of the outdoors. Permanent DST means you’ve got more sun later, like during the hours you’ve got free after work. Permanent ST means you’ve got more sun earlier, like when you’re driving into work. There’s been a lot of talk lately about stopping the twice-yearly time change and selecting one of these as our year-round system.
If we’re picking between these two, we’ve got to go with permanent Standard Time.
Look, I know it sucks to have it be dark outside after work. I know having a little more light when you commute home feels better than doing it in the dark.
But short days are a consequence of winter, not Standard Time. Getting more light in the evening means giving it up in the morning, and losing light in the morning is worse than losing it in the evening.
Imagine you get up for work at 7:00 am local time every day, without fail, and you turn off all your lights at exactly 11:00 pm (or 23:00) every day, without fail. You’re at your job from 9 to 5, and your only chances to see the sun are between 7:00 am and 9:00 am, and after work. We can use mathematical models of circadian rhythms to predict what your melatonin profile—your body’s biological signal for night—would look like on both ST and pDST.
Since sunrise and sunset depend on location, we can first ask: What’s the melatonin profile of a person in Miami look like in the middle of the winter on ST and pDST? Here’s what we get when we do this:
The model predicts they’ll have a lot more melatonin in their body when their alarm goes off if they’re on pDST than they would have on ST (I’ve put a box around this part to highlight it). Having more melatonin when your alarm goes off should make it harder to get up and make you feel groggier. After all, you’re trying to start your day during your body’s biological night.
The difference between the two schedules in this simulation is coming from the fact that, for people on pDST, light exposure is much lower in the morning and much greater in the evening, which late-ifies them (or “phase delays” them; makes them more of a night owl). This happens even though they’re turning off their lights at 11:00 pm each night: that late-in-the-day light is still shoving their rhythms later.
It’s not going to be the same in every location. Someone in Boston on the same day would be waking up with even more melatonin in their body when their alarm goes off under pDST than they would be on ST:
And this is with lights-off fixed at the same time every night! In reality, later light would be expected to shift people’s bedtime later, both by simply delaying them, but also through the positive feedback loop that light in the evening has, where you don’t feel tired, so you keep the lights on, so you late-ify yourself more, so you don’t feel tired, and so on. This asymmetry in how the timing of light changes biology and behavior is important not only for when we just talk about winter, but summer as well. If we go with permanent Standard Time, will the sun rise super early at some times of the year? Yep, I fully own this. But early-in-the-day light doesn’t trigger a behavioral feedback loop the way late-in-the-day light does. And even if you’re totally unconvinced by my beautiful simulations and elegant mathematical arguments, let us not forget that we did pDST in the 70s and didn’t even last a year.
The code for these simulations is on this GitHub repo, and the exact numbers will depend on your assumptions, including when you normally wake up, go to bed, and the light you get at work and at home. The results will be different for a person who never gets up until 10 am or for people who have plenty of opportunity to see the sun during their work day. Plus, mathematical models are always, at best, approximations of what’s going on in a complicated, messy human body.
The point I’m trying to make, though, is all about the trends: later sunlight drags your body’s clock later, making it so you’re trying to start the next day when your body’s still in night mode. And the pain will be felt differently in different places at different times of the year.
So on top of making it so we don’t have to worry about time changes twice a year, permanent Standard Time is the option that best aligns our body’s clocks and the social clocks we’ve hardcoded into society. Things like school start times, work times: these are the social tugs that would make a lot of us wake up in the dark (before our bodies are ready) if we adopted pDST.
And sure, we could shift the times of all human activities—school, work, lunch, anything on the calendar—to be later. But if we make sunrise later and everything else later too, we’d end up basically where we started. Permanent standard time, please.
