Daylight Saving Time (DST)

How and When Did Daylight Saving Time Start? 

A. Benjamin Franklin--of "early to bed and early to rise" fame--was apparently the first person to suggest theconcept of daylight savings. While serving as U.S. ambassador to France in Pads, Franklin wrote of beingawakened 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 he and others rose before noon and burned less midnight oil,Franklin, tongue half in cheek, wrote to a newspaper. 
B. 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. 
C. During World War II the U.S. made daylight saving time mandatory(强制的.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 daylight saving time was observed year-round, essentially making it the new standard time, 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. 
Daylight Saving Time: Energy Saver or Just Time Sucker? 
D. In recent years several studies have suggested that daylight saving time doesn't actually save energy—andmight 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 savingtime for the 2000 Sydney Olympics and others did not. The researchers found that the practice reducedlighting and electricity consumption in the evening but increased energy use in the now dark mornings—wiping out the evening gains. That's because the extra hour that daylight saving time adds in the evening is ahotter hour. "So if people get home an hour earlier in a warmer house, they turn on their air conditioning," theUniversity of Washington's Wolff said. 
E. 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 daylight saving time reduces annual U.S. electricity consumptionby 0.03 percent and overall energy consumption by 0.02 percent. While those percentages seem small, theycould represent significant savings because of the nation's enormous total energy use. 
F. What's more, savings in some regions are apparently greater than in others. California, for instance, appears tobenefit most from daylight saving time--perhaps because its relatively mild weather encourages people to stayoutdoors later. The Energy Department report found that daylight saving time resulted in an energy savings ofone percent dally in the state. 
G. But Wolff, one of many scholars who contributed to the federal report, suggested that the numbers weresubject to statistical variability (变化.and shouldn't be taken as hard facts. And daylight savings' energygains in the U.S. largely depend on your location in relation to the Mason-Dixon Line, Wolff said. "The Northmight 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 daylightsaving." 
Daylight Saving Time: Healthy or Harmful? 
H. For decades advocates of daylight savings have argued that, energy savings or no, daylight saving time boostshealth by encouraging active lifestyles--a claim Wolff and colleagues are currently putting to the test.   "In anationwide American time-use study, we're clearly seeing that, at the time of daylight saving time extension inthe spring, television watching is substantially reduced and outdoor behaviors like jogging, walking, or goingto the park are substantially increased," Wolff said. "That's remarkable, because of course the total amount ofdaylight in a given day is the same. " 
I. But others warn of ill effects. Till Roenneberg, a university professor in Munich (慕尼黑), Germany, said hisstudies show that our circadian (生理节奏的)body clocks--set by light and darkness--never adjust togaining an "extra" hour of sunlight to the end of the day during daylight saving time. 
J. One reason so many people in the developed world are chronically (长期地.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 dothe same things to the body in the morning and the evening. More light in the morning would advance thebody clock, and that would be good. But more light in the evening would even further delay the body clock. " 
K. 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 time change.  "The most likely explanation to ourfindings is disturbed sleep and disruption of biological rhythms," One expert told National Geographic Newsvia email. 
Daylight Savings' Lovers and Haters 
L. With verdicts  (定论.on the benefits, or costs, of daylight savings so split, it may be no surprise that theyearly time changes inspire polarized reactions. In the U.K., for instance, the Lighter Later movement—part of10:10, a group advocating cutting carbon emissions—argues for a sort of extreme daylight savings. First, theysay, move standard time forward an hour, then keep observing daylight saving time as usual—adding twohours of evening daylight to what we currently consider standard time. The folks behind Standardtime.com, onthe other hand, want to abolish daylight saving time altogether, calling energy-efficiency claims "unproven. " 
M. 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 agreedwith that statement, while only 40 percent disagreed. But Seize the Daylight author David Prerau said hisresearch 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."