National Geographic News
Photo of a municipal employee resetting a large clock for daylight savings time in the center of Minsk.

A man resets a large clock for daylight saving time in Minsk, Belarus.

Photograph by Alexey Gromov, AFP/Getty

Brian Handwerk

National Geographic

Published October 28, 2013

With an extra hour of sleep and an earlier sunset, daylight saving time (also called daylight savings time) ends this weekend.

That means clock confusion is once again ticking away, giving rise to hotly debated questions: Why do we spring forward and fall back? Does daylight saving time (DST) really save energy? Is it bad for your health? Here are some answers from the experts.

When Will Daylight Saving Time End in 2013?

For most Americans daylight saving time will end with a "fall back" to standard time on Sunday, November 3, at 2 a.m. Most states "sprang forward" an hour to begin DST on Sunday, March 10. (Read about the start of 2013 daylight saving time.)

But the federal government doesn't require U.S. states or territories to observe daylight saving time, which is why residents of Arizona (except for residents of the Navajo Indian Reservation), Hawaii, Puerto Rico, the Virgin Islands, American Samoa, Guam, and the Northern Marianas Islands won't need to change their clocks this weekend.

Around the world the observance of DST remains very much a mixed bag. In Russia, which abolished daylight saving time in 2011, dark mornings are so unpopular that a coalition in the nation's Duma have proposed legislation to reinstate the practice by the end of this year.

Meanwhile in Japan, which hasn't observed DST in over 60 years, some politicians suggest a return could help ease the nation's post-Fukushima energy crunch.

Brazil seems to split the difference. While only parts of the sprawling nation observe daylight saving time, those regions include major cities like Brasilia, Sao Paulo, and Rio de Janeiro. Brazil's electric utility estimates that DST saves some U.S. $200 million a year, largely by easing urban power demand on hot summer days.

Where it is observed, DST has been known to cause problems.

National surveys by Rasmussen Reports, for example, show that 83 percent of respondents knew when to move their clocks ahead in spring 2010. Twenty-seven percent, though, admitted they'd been an hour early or late at least once in their lives because they hadn't changed their clocks correctly.

So why do we use daylight saving time in the first place?

How and When Did Daylight Saving Time Start?

Ben Franklin—of "early to bed and early to rise" fame—was apparently the first person to suggest the concept of daylight saving time, according to computer scientist David Prerau, author of the book Seize the Daylight: The Curious and Contentious Story of Daylight Saving Time.

While serving as U.S. ambassador to France in Paris, Franklin wrote of being awakened at 6 a.m. and realizing, to his surprise, that the sun rose far earlier than he usually did. Imagine the resources that might be saved if he and others rose before noon and burned less midnight oil, Franklin, tongue half in cheek, wrote to a newspaper.

"Franklin seriously realized it would be beneficial to make better use of daylight, but he didn't really know how to implement it," Prerau said.

It wasn't until World War I that daylight savings were realized on a grand scale. Germany was the first state to adopt the time changes, to reduce artificial lighting and thereby save coal for the war effort. Friends and foes soon followed suit.

In the U.S. a federal law standardized the yearly start and end of daylight saving time in 1918—for the states that chose to observe it.

During World War II the U.S. made daylight saving time mandatory for the whole country, as a way to save wartime resources. Between February 9, 1942, and September 30, 1945, the government took it a step further. During this period DST was observed year-round, essentially making it the new standard time, if only for a few years.

Since the end of World War II, though, daylight saving time has always been optional for U.S. states. But its beginning and end have shifted—and occasionally disappeared.

During the 1973-74 Arab oil embargo, the U.S. once again extended daylight saving time through the winter, resulting in a one percent decrease in the country's electrical load, according to federal studies cited by Prerau.

Thirty years later the Energy Policy Act of 2005 was enacted, mandating a controversial month-long extension of daylight saving time, starting in 2007.

But does daylight saving time really save any energy?

Daylight Saving Time: Energy Saver or Just Time Sink?

In recent years several studies have suggested that daylight saving time doesn't actually save energy—and might even result in a net loss.

Environmental economist Hendrik Wolff, of the University of Washington, co-authored a paper that studied Australian power-use data when parts of the country extended daylight saving time for the 2000 Sydney Olympics and other parts did not. The researchers found that the practice reduced lighting and electricity consumption in the evening but increased energy use in the now-dark mornings—wiping out the evening gains.

Likewise, Matthew Kotchen, an environmental economist at Yale, saw in Indiana a situation ripe for study.

Prior to 2006 only 15 of the state's 92 counties observed daylight saving time. So when the whole state adopted DST, it became possible to compare before-and-after energy use. While use of artificial lights dropped, increased air-conditioning use more than offset any energy gains, according to the daylight saving time research Kotchen led for the National Bureau of Economic Research in 2008.

That's because the extra hour that daylight saving time adds in the evening is a hotter hour. "So if people get home an hour earlier in a warmer house, they turn on their air conditioning," the University of Washington's Wolff said in 2011.

In fact, Hoosier consumers paid more on their electric bills than before they made the annual switch to daylight saving time, the study found. (Related: "Extended Daylight Saving Time Not an Energy Saver?")

But other studies do show energy gains.

In an October 2008 report to Congress, mandated by the same 2005 energy act that extended daylight saving time, the U.S. Department of Energy asserted that springing forward does save energy.

Extended daylight saving time saved 1.3 terawatt hours of electricity. That figure suggests that the practice reduces annual U.S. electricity consumption by 0.03 percent and overall energy consumption by 0.02 percent.

While those percentages seem small, they could represent significant savings because of the nation's enormous total energy use.

What's more, savings in some regions are apparently greater than in others.

California, for instance, appears to benefit most from daylight saving time—perhaps because its relatively mild weather encourages people to stay outdoors later. The Energy Department report found that DST resulted in an energy savings of one percent daily in the state.

But Wolff, one of many scholars who contributed to the federal report, suggested that the numbers were subject to statistical variability and shouldn't be taken as hard facts.

And DST's energy gains in the U.S. largely depend on your location in relation to the Mason-Dixon Line, Wolff said.

"The North might be a slight winner because the North doesn't have as much air conditioning," he said. "But the South is a definite loser in terms of energy consumption. The South has more energy consumption under daylight saving."

(See in-depth energy coverage from National Geographic News.)

Daylight Saving Time: Healthy or Harmful?

For decades advocates of daylight saving time have argued that, energy savings or no, the practice boosts health by encouraging active lifestyles—a claim Wolff and colleagues have put to the test.

"In a nationwide American time-use study, we're clearly seeing that, at the time of daylight saving time extension in the spring, television watching is substantially reduced and outdoor behaviors like jogging, walking, or going to the park are substantially increased," Wolff said. "That's remarkable, because of course the total amount of daylight in a given day is the same."

But others warn of ill effects.

Till Roenneberg, a chronobiologist at Ludwig-Maximilians University in Munich, Germany, said in 2010 his studies show that our circadian body clocks—set by light and darkness—never adjust to gaining an "extra" hour of sunlight at the end of the day during daylight saving time.

"The consequence of that is that the majority of the population has drastically decreased productivity, decreased quality of life, increasing susceptibility to illness, and is just plain tired," Roenneberg said.

One reason so many people in the developed world are chronically overtired, he said, is that they suffer from "social jet lag." In other words, their optimal circadian sleep periods are out of whack with their actual sleep schedules.

Shifting daylight from morning to evening only increases this lag, he said.

"Light doesn't do the same things to the body in the morning and the evening. More light in the morning would advance the body clock, and that would be good. But more light in the evening would even further delay the body clock."

Other research hints at even more serious health risks.

A 2008 study in the New England Journal of Medicine concluded that, at least in Sweden, the risk of having heart attack goes up in the days just after the spring time change. "The most likely explanation to our findings are disturbed sleep and disruption of biological rhythms," lead author Imre Janszky, of the Norwegian University of Science and Technology, said in 2010. (Related: "Leap Year: How the World Makes Up for Lost Time.")

Daylight Savings Lovers, Haters

With verdicts on the benefits and costs of daylight saving time so split, it may be no surprise that the yearly time changes inspire polarized reactions.

In the U.K., for instance, the Lighter Later movement—part of 10:10, a group that advocates cutting carbon emissions—argues for a sort of extreme daylight saving time. First, they say, move standard time forward an hour; then keep observing DST as usual, adding two hours of evening daylight to what we currently consider standard time.

The folks behind StandardTime.com, on the other hand, want to abolish daylight saving time altogether. Calling energy-efficiency claims "unproven," they write: "If we are saving energy let's go year round with Daylight Saving Time. If we are not saving energy let's drop Daylight Saving Time!"

But don't most people enjoy that extra evening sun every summer? Even that remains in doubt.

National telephone surveys by Rasmussen Reports from spring 2010 and fall 2009 deliver the same answer. Most people just "don't think the time change is worth the hassle." Forty-seven percent agreed with that statement, while only 40 percent disagreed.

Seize the Daylight author Prerau said his own research on daylight saving time suggests most people are fond of it.

"I think the first day of daylight saving time is really like the first day of spring for a lot of people," Prerau said. "It's the first time that they have some time after work to make use of the springtime weather.

"I think if you ask most people if they enjoy having an extra hour of daylight in the evening eight months a year, the response would be pretty positive."

72 comments
Francisco Perez
Francisco Perez

Maybe i'm crazy, but I don't understand why we "fall back" in the fall! It gets dark at 4:30pm making the rest of the night such a drag and very uneventful... in fact, in my oppinion we should spring forward in the fall as to create an atmosphere for even more sunlight at night in the winter months, allowing people to actually do things and make the most of their time after work. 

David MacMillan
David MacMillan

I am a skier and the time shift takes away an hour of outdoor activity on the ski slopes. 

Melissa Kimak
Melissa Kimak

I suffer from seasonal depression so I would like to have daylight saving time all year

long.

Maguisa Fernand
Maguisa Fernand

I strongly agree we should move the clock one hour forward during the winter. This time changing is a trick from the government to have us consumers spent more electricity during the winter to keep America rolling. Meanwhile we think we are getting longer hours. What a scam!!!

Mihajlo Filipovic
Mihajlo Filipovic

People are ruled by invention of time, another category of non-existent things in Nature. There are dusks and dawns, days and nights... all else is just hype, tradition, belief, business, stress generator, and watch sale.

But it kinda does take a retirement to understand that, as I now live by celestial display only. And that's a lot of daylight saving principle.

The only proper use I ever got from the thing was some safety in diving. The rest of the experience can be summed up as a lot of guilt-feeling and never ending hurry.

On the first day of my retirement I took my wrist watch off my arm, and to this day I don't know where it is - may God rot its battery to Hell :)

Yo Mama
Yo Mama

Daylight Savings is like cutting off your head to stand on it so you'll be taller.

Anna Costello
Anna Costello

I love falling back. Not a fan of springing forward.

W VODA
W VODA

More light in the morning or more in the evening, WHY should I care?  I'm an adult, I adjust.  I see NO "savings" in MY bills/expenses.  The whole purpose of artificial light is so we humans DON'T have to depend on the Sun for it!!  Luddites!!

W VODA
W VODA

Light in the morning or light in the evening.  You just exchange one for the other.  WHY CARE???  I'm an adult. I adjust.  NO "savings"  that I've seen!

Matthew Thompson
Matthew Thompson

Essentially the same result would be achieved by changing work hours. If work and business hours adjusted once every season, say on the solstices and equinoxes, would it really cause any more confusion? The psychological effect may be worthwhile. Sometimes the shift would have you getting off work at an earlier hour, sometimes going in at a later hour. Obviously, the workday wouldn't truly be offset because of the hour on the other end. Even knowing consciously that you're still working the same amount of time, the idea of getting off early or going in late is a lot more alluring than changing clocks. :)

Samantha Seng
Samantha Seng

I say let's do all year round with Daylight Saving Time

Or, drop it altogether, and just stick with Standard Time

This spring forward and fall back thing is confusing !!

It's confusing, and time conflicting to other part of the world, too.

Dan Alvírez
Dan Alvírez

As afraid of the dark as America has become, it seems the energy savings must be less than minimal.  We light up the night as though it is the day, so now it seems pointless.  I say abolish it.

Shanti Agrawal
Shanti Agrawal

It is useless exercise,and not good to one'health

douglas kostyk
douglas kostyk

Use standard time all year. Clocks were standardized to avoid time conflicts, now we are creating semiannual conflicts.

Neil Wilson
Neil Wilson

If DST helps the more northern states and hurts those south of the Mason-Dixen line, why don't they just divy things into more time zones. The Northern States on DST year-round and the Southern States not on DST?

Linda Bondy
Linda Bondy

I hate the time change.  There are states that don't do it & they seem to be just fine.

Esther Barnett
Esther Barnett

I loathe DST and have never benefited from it. My bills stay the same, the amount of light outside does not affect how late I'm up or if I go out, and the only thing it does is cause me problems. Screw DST, it's just another distraction and hassle from micro-management.

Robert Rode
Robert Rode

Did you ever think that the guy in the clock has to turn the minute hand all the way around 360 degrees because that is the only way the hour hand will move-like changing your conventional wrist watch !!

Robert Rode
Robert Rode

I live in Saskatchewan.We never change our time-it is always daylight savings.Seems we are the only ones in Canada who don't change time twice per year.This obviously is a Government decision. 

Joy Saldanha
Joy Saldanha

I was born & bred in India,so time change just did'nt happen. I live here now, and must now live with "leap forward,fall back" Sooooo what, I do! No big song and dance about it. Get with it guys, There's more than this to ponder & worry about.....Joyo. 

Jeremy Peirson
Jeremy Peirson

What a to do about nothing, as they say!! Live in the tropics and there's no problem!

Tracey Wince
Tracey Wince

Personally, I don't know what the fuss of "changing the clocks" is all about.  For heaven's sakes, you all have been dealing with it since you were BORN.  It allows for extra daylight in the spring and summer when we all can enjoy the outdoors, yet allows our children to travel to school in the daylight hours for the most part.  I too would like to have an extra hour of daylight in the winter but would NOT like it to be dark at 9am . . . just deal with it folks and move on with your lives.

Tom Cassidy
Tom Cassidy

I say stop all the clocks at 1:00PM, so we can golf all year.

Liz F.
Liz F.

As a person who has trouble driving at night, I love DST, hate it when it springs back. After work I can get to workout and do my errands and shopping without endangering any lives!  Like someone else here said, I'm at work in the morning anyway - I don't get to work till 8 so no, I'm not commuting in the dark in case someone was going to bring that up. 

Once the time changes, I come home earlier, turn on my lights, my computer, my tv, and this time of year, turn up the heat.  Of course that takes more energy, seems pretty obvious to me.  It takes me about a week to adjust to the new times; I can't fathom people who say it screws them up all year. 

Nick Angel
Nick Angel

Daylight saving time --- whatever that means ---has been put to practice by individuals

aware of accomplishing more when every bit of daylight is used. And, incidentally save

electricity expenses or energy consumption.  What's wrong with that ?

The government's adjustment of the office working hours is because there come the

days when daylight does not jibe with 'fixed' office working hours necessitating the

use and therefore consumption of electrical energy with costs.

This concept cannot be applied to all types of works, (jobs) however. So, there lies the differences of seeing it.

(To factor in the energy consumed by air conditioning seems irrelevant).

Jose Fco Altamirano Henaro
Jose Fco Altamirano Henaro

"Only the Government would think that you can cut off a foot of the top of a blanket sew it on the bottom and think you have a longer blanket".

Bryan Busch
Bryan Busch

I personally think we should observe DST year round and abolish falling back to standard time. Nothing is more depressing than driving home from work in the dark. I can't get anything done during fall and winter in the evenings because there is no light outside.

Denise Burrell Hunter
Denise Burrell Hunter

Michigan in the Winter is already a depressing state of mind. It would be nice to do as @Bill Hahn said...move it up another hour to allow for more daylight in the evening hours. Being pitch black at 5p.m. is no fun!

David Rouleau
David Rouleau

In Arizona,the biggest time problem is NOT daylight savings time,but just  when is siesta time starts,and when does it end !!!

Paul DeCroix
Paul DeCroix

I prefer daylight savings time. I don't care for it getting dark outside @4:30pm. I much more prefer around 8:pm like in the late spring thru summer. I hate late fall & winter!  

Beth Moore
Beth Moore

Also work 9pm to 5am & be in the dark so much, no wonder I get depressed every oct. Time change sucks.

Beth Moore
Beth Moore

Living in Michigan & being at the far left of the eastern time zone we end up with more darkness then lite, why screw with the time anyway.

Alan Cooper
Alan Cooper

In states like Wisconsin, Minnesota, Iowa, Illinois, Missouri, etc., people interested in Little League baseball, youth and adult softball, and evening golf requested their legislatures institute DST so more daylight was available in the evening.  But the vast majority of farmers did NOT want it as the early morning light was more to their liking.

DeWayne Dukes
DeWayne Dukes

Living in AZ and working in CA I like the hour drive of leaving at 6:00am and arriving at 6:00am. it's like a blank hour.

Bill Hahn
Bill Hahn

Instead of setting the clock back for the winter, they should move it another hour forward.  That way you could get at least some sunlight after work in most places.  I don't care about the morning, I'm in my car or my office in the morning.  But even a little extra sunshine in the afternoon and early evening would be nice.

Cristy Elliott
Cristy Elliott

I'm in AZ where DST is not practiced, as a result I never know if we are 'Pacific time' or 'Mountain time'... I just look up Pacific time on a world clock and compare it to our state's time to get my answer... no big deal. I don't see the point of changing the clocks, it seems silly to me, as it's not truly buying anymore daylight. If I was running late for work I couldn't just change my clock to declare myself on time, after all! In AZ, the occupations that reply on sunrise for work start times just adjust a few times a year, for example start time at 5am or 5:30 instead of 6am for certain months.

George Young
George Young

@Francisco Perez http://wh.gov/ixqo1 I have recently created an online petition to do just what you have mentioned here: Fall FORWARD and Spring BACK!


Dorian Mattar
Dorian Mattar

@Tracey Wince Speak for yourself, I lived in the tropics for half my life and the change of time is definitely a burden on my sleep.  My parents are still there and the time change is always a hassle.

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