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Spring Forward, Cut Back?Does daylight-saving time really save energy?

By Daniel Engber
Posted Friday, March 9, 2007, at 2:12 PM ET

Daylight-saving time begins on Sunday this year, three weeks earlier than normal. The change comes from a 2005 law that aimed to reduce energy costs by limiting our consumption of oil. In an "Explainer" column printed two years ago and reproduced below, Daniel Engber described how the new system could save money.

Springing forward. Click on image to expand.

Congress is on the verge of passing a new energy bill this week that would make daylight-saving time last from mid-March to early November. (It now runs from April through October.) The sponsors of the daylight amendment say it will save the country at least $180 million in energy costs. Why does resetting your clock save oil?

Because people tend to waste several hours of natural light each day. Most of us wake up well after the sun rises and go to sleep long after it sets. If we spent more waking hours when the sun is out, we wouldn't need to use as much electricity to illuminate our surroundings.

Springing forward has its trade-offs. When you set your clocks forward, you exchange morning daylight for a later sunset. Later sunsets tend to get people out of the house more in the evenings, which could lead to an increase in driving (and gasoline use) and a reduction in the use of household appliances. And if daylight time extended too far into the winter, more people would wake up before sunrise and turn on the lights. Government research from the 1970s suggests that extended daylight-saving time produces a modest but significant energy savings of about 1 percent. A British experiment with extended daylight time in the late 1960s failed to produce much corroborating evidence.

American daylight-saving time began in 1918 as a way to conserve energy for World War I. (Germany adopted it two years earlier; British "summer time" followed soon thereafter.) But our six-month schedule of clock changes was repealed just after the war in deference to farmers, whose sun-based schedule works best when the rest of the world is on a standard clock. FDR signed a more extreme form of daylight-saving time into law during World War II, also to save fuel. "War time" set the clocks forward one hour on a permanent basis, without a fall-back. Once again, the law was repealed during peacetime.

In 1966, the federal government devised an official six-month daylight-saving schedule, although each state could choose whether to observe it. The OPEC oil embargo led President Nixon to sign the Emergency Daylight Saving Time Energy Conservation Act. Clocks were set forward to save energy in the winter of 1974, and daylight-saving time lasted for eight months in 1975.

While it did save energy, Nixon's act also increased the number of morning traffic accidents involving schoolchildren. These "dark morning" incidents were offset by a reduction in child accidents later in the day, but the government returned to the six-month schedule for 1976. Under Reagan, an extra month was added again at the urging of business groups (like sports equipment and barbecue grill manufacturers) who expected increased profits with longer days.

If the energy bill passes this week, daylight-saving time would once again extend to eight months. Farmers have not lobbied against the bill, but concerned parents and religious groups have said it puts schoolchildren in danger.

Got a question about today's news? Ask the Explainer.

Explainer thanks Mayer Hillman of the Policy Studies Institute, and David Prerau, the author of Seize the Daylight: The Curious and Contentious Story of Daylight Saving Time.

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Daniel Engber is an associate editor at Slate. He can be reached at .
Photograph of clock by Jack Hollingsworth/Getty Images.
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