Saturday, March 10, 2007

Apple #230: Daylight Saving Time

I am absolutely thrilled that already, two faithful Daily Apple readers have asked me to tell them more about their favorite places. And I will do so shortly. But for today, I got the idea to write an entry about Daylight Saving Time, and since it goes into effect early tomorrow morning, I have to strike while the clock is ticking!

Plus, maybe two weeks ago, I walked into a conversation in which several people were roundly abusing Daylight Saving Time. It's stupid, they said. It's annoying, and what is the purpose of it anyway? (To this, I replied, it saves a ton of money, but more on that shortly).

They also said, why can't we just split the difference and move our clocks ahead half an hour and keep it that way all year long?

A valid question, thought I. So, I give you Daylight Saving Time (note the use of the singular, "Saving"):

(Photo from Timebooth, an anti-DST site)

  • The amount of daylight varies around the globe. For countries nearer the Equator, day and night are roughly 12 hours each. But for countries closer to the poles, daylight can last a lot longer during the summer, and can be much shorter during the summer.

Because of the Earth's tilt, people who live closer to the Poles have more daylight during the summer.
(Diagram from the George F. Cram Company)

  • Daylight Saving Time was enacted to try to make the most of the natural light that occurs on the longer summer nights. If you are awake and active during the times the sun is shining, you're less likely to turn on a lamp. If you can turn on fewer lamps or light them for less time, you can save electricity.
  • In the United States, Daylight Saving Time cuts electricity usage by 1% each day. A pittance, you say? Here's how the data for electricity consumption in the U.S. breaks down:
    • In 2005, industry, transportation, consumers like you and me -- everybody together used 3.8 billion megawatthours of electricity.
    • That works out to be over 10.4 million megawatthours per day.
    • 1% of that, the amount conserved by implementing Daylight Saving for just one day, is more than 1 million megawatthours.
    • Daylight Saving Time (DST) begins this year on March 11 and ends on November 4. That's 238 days. So that means, by moving our clocks ahead one hour, the United States this year will conserve an estimated 238 million megawatthours of electricity.
    • And this is in terms of electricity only. This doesn't take into account the amount of fuel required to generate that much electricity, nor does it take into account other types of power usage.
    • Back in 1975, the Department of Transportation estimated that Daylight Saving Time saved 10,000 barrels of oil -- per day. (1 barrel = 42 gallons)

In 1999, artists Christo and Jean-Claude made an installation called The Wall of 13,000 barrels of oil atop a gasometer. The oil barrel structure measured 85 feet tall by 223 feet wide. So that's what 13,000 barrels of oil -- just slightly more than what we save per day thanks to Daylight Saving Time -- looks like.
(Photo from A Weekly Dose of Architecture)

  • Electricity savings have been estimated to be even higher in other countries. New Zealand, for example, found that power usage dropped 3.5% during DST.
  • Besides saving power, Daylight Saving Time saves lives. People find it easier to see while driving their cars when it's light out, and they're less likely get into collisions. This is why studies have found that the net number of traffic accidents and fatalities has dropped because of the implementation of DST. (Though some people have argued the opposite, that more people get in accidents because they're still sleepy due to DST.)

  • Some people think that we instituted DST because the farmers like it, but actually they don't. They have to get up with the sun and the animals, no matter what the clock says. DST means that they also have to adjust the times when they buy and sell their goods to non-farmers.
  • Benjamin Franklin was the first person in the US known to have proposed moving our clocks to save energy. He wrote his proposal in 1784.
  • DST was first implemented in the US in the 1880's to keep train schedules accurate. Even so, it wasn't a widespread practice until World War I, when the country very much wanted to conserve fuel. After the War, it fell out of practice again.
  • It was instituted again more formally during the oil embargo in the mid-1970's, though individual states could choose not to participate (Indiana was one of those states).

Anybody else remember this? (cars lining up for gas in 1973, during the oil embargo)
(Photo by Marty Lederhandler, used by The New York Times)

  • Over time, more states have switched to DST, although territories near the Equator such as Puerto Rico and Guam do not move their clocks because they'd see very little benefit from it. California, however, is looking into instituting double-DST in the summer and DST in the winter.

  • Okay, all that's very nice, but let's get to the real question, which is why do we have to move our clocks one hour two times each year? Why can't we split the difference and move our clocks ahead one half hour once, and be done with it?
  • As far as I can figure out, there isn't any reason why we couldn't do this. The reason why we move our clocks specifically one hour as opposed to some other increment of time has nothing to do with the position of the Earth relative to the sun or anything like that.

Standard time zones around the world. As you can see, the time zones get all funky in lots of places, especially around Australia and Indonesia and Hawaii.
(Map from Tyler's Territory)

  • In other countries, their time zones even within the country sometimes differ by half an hour, or some are even forty-five minutes apart. I haven't seen any explanation for the reason we move our clocks an hour and not some other time increment. So it looks like, if we really wanted to make it a half-hour instead, and if we could make a compelling case for it, we could beseige our legislators and make them change it.
  • I have to say, though, you might find it hard to argue against saving an extra 5,000 barrels of oil a day just because you find it annoying to move your clock twice a year. Or at least, you'd have trouble making that argument stick with me.

Web Exhibits, Daylight Saving Time
Department of Energy, Direct Use and Retail Sales of Electricity to Ultimate Customers by Sector, by Provider, October 4, 2006
California Energy Commission, Saving Time, Saving Energy
End Daylight Saving Time
NASA Science Question of the Week, Does anyone really know what time it is?


  1. But I've also read that Daylight Saving Time increases heating-energy consumption by more than it saves in electricity; in other words, that it's a net drain on the environment.

  2. ML, I believe the study to which you are referring is the one that was done in Indiana. That study did find that in that state, daylight saving time did result in a 1% to 4% increase in energy usage because of the increase in heating costs.

    Conversely, two similar studies done in California found that there was a marginal decrease in energy costs because of the reduced use of air conditioning.

    New studies are being conducted on a nation-wide level to determine the effects on all energy usage. Results of those studies are expected in the next year or two.

  3. Ummm ... isn't is supposed to be hyphenated, as in Daylight-Saving Time?!?!?

  4. Hey, Mr. Anonymous Reporter,

    "Daylight saving time (DST) is considered to be the correct term for the practice of advancing clocks to save energy because it refers to a time for saving daylight."

    The use of the hyphen is considered an alternate variation which is sometimes used in news reports.


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