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Daylight Saving Time (DST)
When Did Daylight Savings Begin in 2012?For most Americans, daylight saving time in 2012 began 2 a.m. on Sunday, March 11, when most statessprang forward an hour. Time fell back to standard time again on Sunday, November 4, 2012, when daylightsaving time ended.
How and When Did Daylight Saving Time Start?
Benjamin Franklin-of "early to bed and early to rise" fame- was apparently the first person to suggest the concept of daylight savings.
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 would rise far earlier than he usually did. Imagine the resources that might be saved if heand others rose before noon and burned less midnight oil, Franklin, tongue half in cheek, wrote to a newspaper.
It wasn't until World War I that daylight savings were realized on a grand scale. Germany was the first stateto adopt the time changes, to reduce artificial lighting and thereby save coal for the war effort. Friends and foessoon 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 (强制的) for the whole country, as away to save wartime resources. Between February 9, 1942, and September 30, 1945, the government took it a stepfurther. During this period daylight saving time was observed year-round, essentially making it the new standardtime, if only for a few years.
Many 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 Suck?
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 studiedAustralian power-use data when parts of the country extended daylight saving time for the 2000 Sydney Olympicsand others did not. The researchers found that the practice reduced lighting and electricity consumption in theevening but increased energy use in the now dark mornings-wiping out the evening gains.
That's because the exwa hour that daylight saving time adds in the evening is a hotter hour. "So if people gethome an hour earlier in a warmer house, they turn on their air conditioning," the University of Washington'sWolff said.
In fact, Hoosier (美国印第安纳州人的) consumers paid more on their electric bills than before they made the annual switch to daylight saving time, the study found.
But other studies do show energy gains.
In an October 2008 daylight saving time 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(太瓦)hours of electricity. That figure suggests that dayfightsaving time reduces annual U.S. electricity consumption by 0.03 percent and overall energy consumption by0.02 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 relativelymild weather encourages people to stay outdoors later. The Energy Department repent found that daylight savingtime resulted in an energy savings of one percent daffy in the state.
But Wolff, one of many scholars who contributed to the federal report, suggested that the numbers were subject to statistical variability (变化) and shouldn't be taken as hard facts.
And daylight savings' energy gains in the U.S. largely depend on your loeation'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. "Butthe South is a definite loser in terms of energy consumption. The South has more energy consumption underdaylight saving. "
Daylight Saving Time: Healthy or Harmful?
For decades advocates of daylight savings have argued that. energy savings or no, daylight saving time boosts health by encouraging active lifestyles--a claim Wolff and colleagues are currendy putting to the test.
"In a nationwide American time-use study, we're clearly seeing that, at the time of daylight saving timeextension in the spring, television watching is substantially reduced and outdoor behaviors like jogging, walking, orgoing to the park are substantially increased," Wolff said. "That's remarkable, because of course the total amountof daylight in a given day is the same."
But others warn of ill effects.
Till Roeuneberg, a university professor in Munich (慕尼黑), Germany, said his studies show that ourcircadian (生理节奏的) body clocks- set by light and darkness- never adjust to gaining an "extra" hour ofsunlight to the end of the day during dayfight saving time.
One reason so many people in the developed world are chronically (长期的) overtired, he said, is that theysuffer from "social jet lag. "In other words, their optimal circadian sleep periods don't accord with their actualsleep schedules.
Shifting daylight from morning to evening only increases this lag, he said. "Light doesn't do the same thingsto the body in the morning and the evening. More light in the morning would advance the body clock, and thatwould 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 concluded that, at least in Sweden, heart attack risks go up in the days just after the spring timechange. "The most likely explanation to our findings is disturbed sleep and disruption of biological rhythms," Oneexpert told National Geographic News via email.
Daylight Savings Lovers and Haters
With verdicts (定论) on the benefits, or costs, of daylight savings 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 advocating cutting carbonemissions-argues for a sort of extreme daylight savings. First, they say, move standard time forward an hour, thenkeep observing daylight saving time as usual--adding two hours of evening daylight to what we currently considerstandard time.
The folks behind Standardtime.com, on the other hand, want to abolish daylight saving time altogether, calling energy-efficiency claims "unproven."
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 (麻烦的事). "Forty-seven percent agreed withthat statement, while only 40 percent disagreed.
But Seize the Daylight author David Prerau said his research on daylight saving time suggests most people are fond of it.
"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."
It can be learnt from the beginning of the passage that___________. A．daylight saving time usually comes in March
B．daylight saving time could be longer than half a year
C．all of the Americans have the same daylight saving time
D．when daylight saving time ends, we spring forward an hour
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