Spring forward

What is Daylight Saving Time? The science behind turning back the clocks

Every spring, for better or worse, most Americans lose an hour of their day.

The classic silver clock on abstract background

In the wee hours of Sunday, March 8, the clock on your phone will appear to glitch. At 2:00 a.m., the clocks will "spring forward," suddenly switching to become 3:00 a.m. The intervening hour will be lost to the ether (and, if you have an alarm set, so will your sleep be rudely curtailed).

Setting the clocks forward and back twice a year for Daylight Saving Time may feel like an old-fashioned habit, but there is a scientific reason why we meddle with time in this way.

This year, Daylight Saving starts at 2:00 a.m. on Sunday, March 8. When the clock strikes two, time will be made to artificially jump forward an hour. If you have an automatically updating clock, and most smartphones do, then you can watch this happen in real time (stay with us), as the read out makes the leap from 1:59 a.m. to 3:00 a.m. Goodbye an hour of sleep, and hello earlier dawns.

But there is a reason why we do this to ourselves.

Who invented Daylight Saving Time?

While living in Paris in 1784, Benjamin Franklin, one of the United States' founding fathers, came up with a novel ruse to save money. He proposed that by changing the clocks to gain and lose an hour at different points of the year, one might save cash buying candles through the longer, darker winter months.

With the changing seasons come shifts in the hours of daylight we get. By waking up earlier (in terms of the Sun’s position), we have more hours of natural light to play with.

It was a simple enough concept, but its application today is moot, to say the least.

When did Daylight Saving Time become standard?

After Franklin first proposed the idea, Daylight Saving Time (DST) was hotly debated through the late 1800s and early 1900s. Not everyone was down with the idea of losing an hour, it seems.

But by the turn of the century, some cities around the world started to adopt the practice, and, during World War 1, “saving” daylight helped to reduce the amount of coal being burned for fuel on the Home Front. It was this that made Daylight Saving Time really take off in the United States and Europe.

In the US, DST became law in 1966, thanks to President Lyndon B. Johnson, who mandated states to sync up their timekeeping in the name of efficiency. But depending on where you live in the US, you might not have to save daylight.

People living in Hawaii do not change their clocks, and neither do folks living in parts of Arizona.

At the Hoover Dam, clocks show the time in Nevada and in Arizona, the latter of which largely doesn't observe Daylight Saving Time.


Does Daylight Saving Time save energy and money?

In the mid-20th century, playing Doctor Who twice a year and switching the clocks forward and back seemed to make a lot of sense as both an energy and money-saving practice.

And while today we rely far less on coal for electricity (or candles for light), there is evidence to suggest that DST still saves cash. In a 2011 study conducted in Norway and Sweden, researchers found that saving daylight reduced annual electricity spending by as many as 30 million Euros (some $34 million).

However, another 2011 study from the US suggests the contrary: Because they used more electricity as a result of Daylight Saving Time, homes in Indiana had increased electricity costs of $9 million a year, the researchers found.

Are there risks to Daylight Saving Time?

Waking up without that extra hour can feel like you have been cheated out of sweet sleep, but researchers are genuinely concerned that DST carries some hidden health risks.

A growing body of research suggests that messing with time messes with our internal body clocks. These internal clocks, also known as our circadian rhythm, regulate sleep and other vital body functions, including the immune system. Disruption to circadian rhythm is a hallmark of certain diseases, including cancer, diabetes, and heart disease.

As Inverse reported in 2019, disrupting the relationship between our internal clocks and the social clock that governs our lives can have serious health effects. But the problem may extend far beyond Daylight Saving Time.

Exposure to the blue light from screens can also upset this natural rhythm, a 2017 study suggests. And a 2018 study finds that Americans may be 75 minutes out of sync as a result of artificial lights allowing us to stay awake longer than there are daylight hours.

At least one study shows that our bodies never really adjust to the time change — even if we rest up, set alarms, and monitor our caffeine intake like experts recommend. In turn, that might mess with how we perceive and adapt to the changing seasons.

So should we scrap Daylight Saving Time? Researchers at the Society for Research on Biological Rhythms say yes, arguing that switching to Standard Time has more benefits to both our health and our societies than does Daylight Saving Time. But so far, the political will to do away with this tradition is not keeping up with the science.

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