Why do we have Daylight Saving Time?

18 December 2020


Clock face


Here in Europe it is dark and cold, and thanks to having switched back to regular time from Daylight Saving Time back in October, it’s even darker in the evenings than otherwise. But where did Daylight Saving Time come from, and is it still a good idea? Eva Higginbotham tried to answer this question back in November...

Eva - Here in Europe the clocks have recently gone back, causing - as usual - much confusion. And it’s not just humans that are missing their appointments; in the words of a Facebook friend, “how do you explain to a cat who routinely gets fed at 4pm that the clocks went back and he is screaming at me an hour early?”

The process of switching back and forth to daylight saving time - or daylight savings time, as most call it - feels unnatural. Why then do we do it?

The concept comes rather surprisingly from Benjamin Franklin, who, on holiday to Paris, saw the locals sleeping in through the early summer mornings and staying up after dark - and wondered whether they couldn’t just shift their schedules to save on candles. It was a bit of a joke - he suggested using cannons to wake everyone up - but by World War 2 many countries had adopted it and it’s stayed with us almost ever since.

For countries farther from the equator, with more pronounced seasons, the idea makes theoretical sense. If you wake up around 6,7,8 am to go to work, you’ll catch the full day’s worth of sun in winter, but miss the sunrise in summer. May as well put the clocks back, make the sunrise effectively happen ‘later’, and catch more daylight.

To understand how it works in practice, though, you’re getting into the complex world of the body clock. Our bodies run on a close to 24-hour rhythm, raising our temperature and blood pressure when it’s time to wake up, controlling our hormone levels throughout the day, releasing melatonin that helps us sleep at night. Each cell has its own clock, which keeps time by a ‘master clock’ in the underside of the brain. And the master clock sets its time by the sunlight.

But - every person is different. The reason you get some being morning larks and some being night owls is because people’s body clocks synchronise with the light differently. You can get data on this by looking at the times people wake up on their days off work - and data from Americans shows that three quarters would prefer to wake up and sleep later. Daylight saving time then moves the official time in the opposite direction to what they’d prefer - increasing what’s called their ‘social jet lag’, and bringing in all sorts of health problems.

So night owls don’t like the new times. Farmers generally don’t like the change, because they wake up with the sun anyway. And whenever people are surveyed on the issue, it’s usually a minority saying they think it’s worth the hassle.

But, does it save energy on lighting houses, as Ben Franklin suggested? There’s evidence from Australia and the USA that reductions in energy demand for lighting were matched by increased demand for air conditioning during the longer daytime. In the words of the University of Washington’s Hendrik Wolff, “everywhere there is air conditioning, our evidence suggests that daylight saving is a loser.”

There’s counter arguments though that the extra light is just good for us. People spend more time outdoors; the roads are lighter for the evening rush hour; and there’s less crime because of the light. In response, others propose: well if it’s so good in summer, why not year round? Perennial daylight saving time - effectively moving your country one time zone to the east.

But that proposition also causes arguments, as it would mean that in the winter, school children and workers would likely be starting their days in pitch darkness, and lots of circadian rhythm experts warn that that would cause harm too.

So, the debate continues, but for now, it seems opinion will keep flip flopping on whether it’s worth making the switch. Which seems pretty appropriate, actually


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