The case against us

Evening light is worth more than morning light

Here is the best version of the argument, and it is genuinely good.

Yes, the window only slides. Granted. But the hours it slides between are not interchangeable, because people are not evenly distributed across the day. At 7am most people are indoors, asleep, or in a car. At 6pm they are walking, cycling, shopping, coaching kids, running errands, and standing in intersections.

An hour of darkness at 7am costs relatively little because few people are exposed to it. An hour of darkness at 5pm costs a great deal because everyone is. If light is a safety good, put it where the people are.

That is not hand-waving. It is arithmetic, and four separate literatures support it.

Four findings that should give us pause

• 366 livesFull-year daylight time would reduce pedestrian fatalities by 171 a year and vehicle-occupant fatalities by 195 a year, in the 5–10am and 4–9pm windows. This is a serious, peer-reviewed estimate and we do not have a refutation of it, only a caveat: it is a simulation that reallocates light while holding behaviour fixed.
• −7% robberyA regression discontinuity at the spring transition finds daily robberies fall 7%, and 27% in the sunset hour itself, worth $59 million a year in avoided social cost from the 2007 extension alone — four extra weeks. The authors note the year-round figure would be far higher. This is the single strongest result in the whole debate on either side.
• 23,188 kidsAccelerometer data on children aged 5 to 16 across nine countries, with the clock change used as the natural experiment: daily activity is higher on days with later sunsets. The authors call the increase small, and it was weak or absent in the US, Brazilian and Madeiran samples — but it is objectively measured rather than self-reported, which is more than most of this literature manages.
• +11% depressionThe sharpest finding against us. In a Danish registry of 185,419 hospital contacts, the transition to standard time is associated with an 11% rise in unipolar depressive episodes lasting about ten weeks — the longest-duration effect anyone has found. The spring transition showed nothing comparable.

The best philosophical objection

Two physicists, Martín-Olalla and Mira, have spent years publishing methodological critiques of the chronobiology in this debate, and their central argument deserves a hearing in a Royal Society journal, which is where it appeared.

Their point: seasonal clock change is not an arbitrary imposition. It is a solution to a real problem. At our latitudes sunrise time swings enormously across the year while work and school schedules stay fixed. Something has to give. Pick permanent standard time and you start the day too late relative to a 4:30am June sunrise, wasting hours of early light. Pick permanent daylight time and you start too early relative to a 9am January sunrise.

Both permanent options fight human physiology. The only question is which season you would rather mis-serve.

If they are right, abolishing the switch is not a clean win at all. It is choosing which half of the year to be wrong in, and the people who designed the switch understood something the abolitionists have forgotten.

And then there is the vote. H.R. 139 passed 308 to 117, with majorities in both parties. Nineteen states have already passed laws to adopt permanent daylight time the moment Congress lets them. Whatever the sleep societies think, this is what the elected representatives of the country have concluded.