Daylight saving time
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Daylight saving time (DST; also summer time in British English) is the convention of advancing clocks so that afternoons have more daylight and mornings have less. Typically clocks are adjusted forward one hour near the start of spring and are adjusted backward in autumn. Modern DST was first proposed in 1907 by William Willett. Many countries have used it since then; details vary by location and change occasionally.
The practice can be controversial.<ref name=Downing-Prerau/> Adding daylight to afternoons benefits retailing, sports, and other activities that exploit sunlight after working hours,<ref name=Benfield/> but causes problems for farming, entertainment and other occupations tied to the sun.<ref name=farming/><ref name=Kissell/> Extra afternoon daylight reduces traffic fatalities;<ref name=Ferguson/> its effect on health and crime is less clear. An early goal of DST was to reduce evening usage of incandescent lighting, formerly a primary use of electricity;<ref name=Bartlett/> changes in usage patterns have cast doubt on whether DST now saves energy.<ref name=Kellogg/>
DST's clock shifts can serve as fire safety reminders,<ref name=USFA/> but they complicate timekeeping and can disrupt meetings, travel, billing, recordkeeping, medical devices, and heavy equipment.<ref name=Neumann/> Many computer-based systems can adjust their clocks automatically, but this can be limited and error-prone, particularly when DST rules change.<ref name=Tong/>
Sommaire |
Origin
Although not punctual in the modern sense, the ancients adjusted daily schedules to the sun more flexibly than modern DST does, often dividing daylight into 12 equal hours regardless of day length, so that each daylight hour was longer during summer.<ref>Modèle:Cite journal</ref> For example, Roman water clocks had different scales for different months of the year: at Rome's latitude the third hour from sunrise, hora tertia, started by modern standards at 09:02 solar time and lasted 44 minutes at the winter solstice, but at the summer solstice it started at 06:58 and lasted 75 minutes.<ref>Modèle:Cite book</ref> After ancient times, equal-length civil hours eventually supplanted unequal, so civil time no longer varies by season. Unequal hours are still used in a few traditional settings, such as some Mount Athos monasteries.<ref>Modèle:Cite journal</ref>
www.historynet.com/magazines/american_history/3036996.html}}</ref> This 1784 satire proposed taxing shutters, rationing candles, and waking the public by ringing church bells and firing cannons at sunrise.<ref name='Franklin'>Modèle:Cite journal Its first publication was in the journal's "Économie" section. The revised English version (retrieved on 2007-05-26) is commonly called "An Economical Project", a title that is not Franklin's; see Modèle:Cite journal</ref> Franklin did not propose DST; like ancient Rome, 18th-century Europe did not keep accurate schedules. However, this soon changed as rail and communication networks came to require a standardization of time unknown in Franklin's day.<ref>Modèle:Cite journal</ref>//www.historynet.com/magazines/american_history/3036996.html}}</ref> This 1784 satire proposed taxing shutters, rationing candles, and waking the public by ringing church bells and firing cannons at sunrise.<ref name='Franklin'>Modèle:Cite journal Its first publication was in the journal's "Économie" section. The revised English version (retrieved on 2007-05-26) is commonly called "An Economical Project", a title that is not Franklin's; see Modèle:Cite journal</ref> Franklin did not propose DST; like ancient Rome, 18th-century Europe did not keep accurate schedules. However, this soon changed as rail and communication networks came to require a standardization of time unknown in Franklin's day.<ref>Modèle:Cite journal</ref>
www.pettswood.org.uk/willett.cfm |date=2007 |accessdate=2007-03-27 |publisher=Petts Wood & District Residents' Association}}</ref> An avid golfer, he also disliked cutting short his round at dusk. His solution was to advance the clock during the summer months, a proposal he published two years later.<ref name='Willett'>Modèle:Cite paper | Modèle:Cite paper</ref> He lobbied unsuccessfully for the proposal until his death in 1915; see Politics for more details. Wartime Germany, its allies, and their occupied zones were the first European countries to use DST, starting April 30, 1916. Britain, most other belligerents, and many European neutrals soon followed suit, Russia and a few other countries waited until the next year, and the United States did not use it until 1918. Since then the world has seen many enactments, adjustments, and repeals.<ref>Modèle:Cite book</ref>//www.pettswood.org.uk/willett.cfm |date=2007 |accessdate=2007-03-27 |publisher=Petts Wood & District Residents' Association}}</ref> An avid golfer, he also disliked cutting short his round at dusk. His solution was to advance the clock during the summer months, a proposal he published two years later.<ref name='Willett'>Modèle:Cite paper | Modèle:Cite paper</ref> He lobbied unsuccessfully for the proposal until his death in 1915; see Politics for more details. Wartime Germany, its allies, and their occupied zones were the first European countries to use DST, starting April 30, 1916. Britain, most other belligerents, and many European neutrals soon followed suit, Russia and a few other countries waited until the next year, and the United States did not use it until 1918. Since then the world has seen many enactments, adjustments, and repeals.<ref>Modèle:Cite book</ref>
Benefits and drawbacks
opencrs.cdt.org/document/RS22284/ |accessdate=2007-06-01 |title= Daylight saving time |publisher= Congressional Research Service |version= Order Code RS22284 |date=2006-04-04}}</ref>//opencrs.cdt.org/document/RS22284/ |accessdate=2007-06-01 |title= Daylight saving time |publisher= Congressional Research Service |version= Order Code RS22284 |date=2006-04-04}}</ref>
www.simson.net/ref/1972/Schelling_Hockey_Helmets.pdf |publisher= W. W. Norton |year=2006 |origyear=1972 |isbn=0-393-32946-1}} Retrieved on 2007-05-26.</ref> The advantages of coordination are so great that many people ignore whether DST is in effect by altering their nominal work schedules to coordinate with daylight, television broadcasts, or remote colleagues.<ref>Modèle:Cite paper</ref>//www.simson.net/ref/1972/Schelling_Hockey_Helmets.pdf |publisher= W. W. Norton |year=2006 |origyear=1972 |isbn=0-393-32946-1}} Retrieved on 2007-05-26.</ref> The advantages of coordination are so great that many people ignore whether DST is in effect by altering their nominal work schedules to coordinate with daylight, television broadcasts, or remote colleagues.<ref>Modèle:Cite paper</ref>
Energy use
commdocs.house.gov/committees/science/hsy73325.000/hsy73325_0.HTM |accessdate=2007-12-14}}</ref> Although energy conservation remains an important goal,<ref>Modèle:Cite journal</ref> statistically significant evidence for it has proved elusive. The U.S. Dept. of Transportation (DOT) concluded in 1975 that DST might reduce the country's electricity usage by 1% during March and April,<ref name=Lawson>Modèle:Cite book</ref> but the National Bureau of Standards (NBS) reviewed the DOT study in 1976 and found no significant energy savings.<ref name='CRS'/> In 2000 when parts of Australia began DST in late winter, overall electricity consumption did not decrease, but the morning peak load and prices increased.<ref name=Kellogg>Modèle:Cite paper</ref> Although a 2007 study estimated that introducing DST to Japan would reduce household lighting energy consumption,<ref name=Fong>Modèle:Cite journal</ref> a 2007 simulation estimated that DST would increase overall energy use in Osaka residences by 0.13%, with a 0.02% decrease due to less lighting more than outweighed by a 0.15% increase due to extra cooling; neither study examined non-residential energy use.<ref>Modèle:Cite journal</ref> A 2007 California study found no clear evidence that electricity would be saved through the earlier start to DST that year,<ref>Modèle:Cite paper</ref> and although one utility did report a decrease in March 2007, five others did not.<ref> Cindy Cline
. " Early daylight saving time hasn't saved energy in Ottawa " , CFRA , 2007-03-21 . Retrieved on 2007-05-16 . | Jim Goddard . " No saving to hydro and gas bill with earlier time change " , News1130 , 2007-04-02 . Retrieved on 2007-05-16 . | Lisa Lee . " Early U.S. Daylight Savings a bust in power savings " , Reuters , 2007-04-02 . Retrieved on 2007-05-16 . | " Daylight saving time reduces power consumption " , AM770CHQR , 2007-04-03 . Retrieved on 2007-05-16 . | Ned Potter . " Final word on daylight saving—not " , ABC News , 2007-04-04 . Retrieved on 2007-05-16 . </ref> DST may increase gasoline consumption: U.S. gasoline demand grew an extra 1% during the newly introduced DST in March 2007.<ref> Shawn McCarthy . " Has daylight saving time fuelled gasoline consumption? " , Globe and Mail , 2007-04-18 . </ref>//commdocs.house.gov/committees/science/hsy73325.000/hsy73325_0.HTM |accessdate=2007-12-14}}</ref> Although energy conservation remains an important goal,<ref>Modèle:Cite journal</ref> statistically significant evidence for it has proved elusive. The U.S. Dept. of Transportation (DOT) concluded in 1975 that DST might reduce the country's electricity usage by 1% during March and April,<ref name=Lawson>Modèle:Cite book</ref> but the National Bureau of Standards (NBS) reviewed the DOT study in 1976 and found no significant energy savings.<ref name='CRS'/> In 2000 when parts of Australia began DST in late winter, overall electricity consumption did not decrease, but the morning peak load and prices increased.<ref name=Kellogg>Modèle:Cite paper</ref> Although a 2007 study estimated that introducing DST to Japan would reduce household lighting energy consumption,<ref name=Fong>Modèle:Cite journal</ref> a 2007 simulation estimated that DST would increase overall energy use in Osaka residences by 0.13%, with a 0.02% decrease due to less lighting more than outweighed by a 0.15% increase due to extra cooling; neither study examined non-residential energy use.<ref>Modèle:Cite journal</ref> A 2007 California study found no clear evidence that electricity would be saved through the earlier start to DST that year,<ref>Modèle:Cite paper</ref> and although one utility did report a decrease in March 2007, five others did not.<ref> Cindy Cline . " Early daylight saving time hasn't saved energy in Ottawa " , CFRA , 2007-03-21 . Retrieved on 2007-05-16 . | Jim Goddard . " No saving to hydro and gas bill with earlier time change " , News1130 , 2007-04-02 . Retrieved on 2007-05-16 . | Lisa Lee . " Early U.S. Daylight Savings a bust in power savings " , Reuters , 2007-04-02 . Retrieved on 2007-05-16 . | " Daylight saving time reduces power consumption " , AM770CHQR , 2007-04-03 . Retrieved on 2007-05-16 . | Ned Potter . " Final word on daylight saving—not " , ABC News , 2007-04-04 . Retrieved on 2007-05-16 . </ref> DST may increase gasoline consumption: U.S. gasoline demand grew an extra 1% during the newly introduced DST in March 2007.<ref> Shawn McCarthy . " Has daylight saving time fuelled gasoline consumption? " , Globe and Mail , 2007-04-18 . </ref>
Economic effects
daylightchart.sourceforge.net/|accessdate=2007-06-25|date=2007-05-15|title=Daylight Chart|author=Sualeh Fatehi|publisher=SourceForge.net}}</ref>]]//daylightchart.sourceforge.net/|accessdate=2007-06-25|date=2007-05-15|title=Daylight Chart|author=Sualeh Fatehi|publisher=SourceForge.net}}</ref>]] www.house.leg.state.mn.us/hinfo/swkly/1995-96/select/time.txt |work= Session Weekly |publisher= Minnesota House Public Information Office |date=1991 |accessdate=2003-03-21 |quote= … the Minneapolis Star, Jan. 28, 1959.… [wrote] 'Farmers complained that they cannot get into the fields any earlier than under standard time … because the morning sun does not dry the dew "on daylight savings time." ' }}</ref> DST also hurts prime-time broadcast ratings<ref name=Kissell> Rick Kissell
. " Daylight-saving dock ratings " , Variety , 2007-03-20 . Retrieved on 2007-05-16 . </ref> and theaters, especially drive-ins.<ref>Modèle:Cite book</ref>//www.house.leg.state.mn.us/hinfo/swkly/1995-96/select/time.txt |work= Session Weekly |publisher= Minnesota House Public Information Office |date=1991 |accessdate=2003-03-21 |quote= … the Minneapolis Star, Jan. 28, 1959.… [wrote] 'Farmers complained that they cannot get into the fields any earlier than under standard time … because the morning sun does not dry the dew "on daylight savings time." ' }}</ref> DST also hurts prime-time broadcast ratings<ref name=Kissell> Rick Kissell . " Daylight-saving dock ratings " , Variety , 2007-03-20 . Retrieved on 2007-05-16 . </ref> and theaters, especially drive-ins.<ref>Modèle:Cite book</ref>
www.csmonitor.com/2007/0307/p02s01-stct.html |accessdate=2007-05-16}}</ref>//www.csmonitor.com/2007/0307/p02s01-stct.html |accessdate=2007-05-16}}</ref>
Public safety
www.pubmedcentral.nih.gov/articlerender.fcgi?pubmedid=7832269 |accessdate=2007-07-14}}</ref> Others have found similar reductions.<ref>Modèle:Cite journal</ref> Single/Double Summer Time (SDST), a variant where clocks are one hour ahead of the sun in winter and two in summer, has been projected to reduce traffic fatalities by 3% to 4% in the UK, compared to ordinary DST.<ref>Modèle:Cite paper</ref> It is not clear whether sleep disruption contributes to fatal accidents immediately after the spring and autumn clock shifts.<ref>Modèle:Cite journal Data supporting Coren's half of this exchange are in: Modèle:Cite conference</ref> A correlation between clock shifts and accidents has been observed in North America but not in Sweden. If this twice-yearly effect exists, it is far smaller than the overall reduction in fatalities.<ref>Modèle:Cite journal | Modèle:Cite journal</ref>//www.pubmedcentral.nih.gov/articlerender.fcgi?pubmedid=7832269 |accessdate=2007-07-14}}</ref> Others have found similar reductions.<ref>Modèle:Cite journal</ref> Single/Double Summer Time (SDST), a variant where clocks are one hour ahead of the sun in winter and two in summer, has been projected to reduce traffic fatalities by 3% to 4% in the UK, compared to ordinary DST.<ref>Modèle:Cite paper</ref> It is not clear whether sleep disruption contributes to fatal accidents immediately after the spring and autumn clock shifts.<ref>Modèle:Cite journal Data supporting Coren's half of this exchange are in: Modèle:Cite conference</ref> A correlation between clock shifts and accidents has been observed in North America but not in Sweden. If this twice-yearly effect exists, it is far smaller than the overall reduction in fatalities.<ref>Modèle:Cite journal | Modèle:Cite journal</ref>
In the 1970s the U.S. Law Enforcement Assistance Administration (LEAA) found a reduction of 10% to 13% in Washington, D.C.'s violent crime rate during DST. However, the LEAA did not filter out other factors, and it examined only two cities and found crime reductions only in one and only in some crime categories; the DOT decided it was "impossible to conclude with any confidence that comparable benefits would be found nationwide."<ref>Modèle:Cite book</ref> Outdoor lighting has a marginal and sometimes even contradictory influence on crime and fear of crime.<ref>Modèle:Cite journal</ref>
blogs.consumerreports.org/home/2007/03/changes_to_dayl.html |accessdate=2007-11-02}}</ref><ref>Modèle:Cite press release</ref><ref name='USFA'>Modèle:Cite press release</ref> This is not an essential function of DST, as locations without DST can instead use the first days of spring and autumn as reminders.<ref> Amy Fackler
(2005-04-08) . Prevent household fires . Yahoo Health
. Retrieved on 2007-05-16. </ref>//blogs.consumerreports.org/home/2007/03/changes_to_dayl.html |accessdate=2007-11-02}}</ref><ref>Modèle:Cite press release</ref><ref name='USFA'>Modèle:Cite press release</ref> This is not an essential function of DST, as locations without DST can instead use the first days of spring and autumn as reminders.<ref> Amy Fackler
(2005-04-08) . Prevent household fires . Yahoo Health
. Retrieved on 2007-05-16. </ref>
Health
moderatrix8.blogspot.com/2007/03/daylight-savings.html |date=2007-03-12 |title= Daylight savings |work= Moderatrix Musings |accessdate=2007-03-28|quote=I now have to drive to work in the dark. This is a real problem for me as I've got terrible night blindness and avoid driving in the dark at all costs. It's just not safe (especially for the other drivers since I can't tell where they are.)}}</ref>//moderatrix8.blogspot.com/2007/03/daylight-savings.html |date=2007-03-12 |title= Daylight savings |work= Moderatrix Musings |accessdate=2007-03-28|quote=I now have to drive to work in the dark. This is a real problem for me as I've got terrible night blindness and avoid driving in the dark at all costs. It's just not safe (especially for the other drivers since I can't tell where they are.)}}</ref>
images.cell.com/images/EdImages/CurrentBiology/Kantermann.pdf |title= The human circadian clock's seasonal adjustment is disrupted by daylight saving time |author= Thomas Kantermann |coauthors= Myriam Juda; Martha Merrow; Till Roenneberg |accessdate=2007-10-27 |laysummary=http://abc.net.au/science/news/stories/2007/2070223.htm |laysource= ABC Science Online, Australia |laydate=2007-10-25}}</ref> The government of Kazakhstan cited health complications due to clock shifts as a primary reason for abolishing DST in 2005.<ref> Kazakhstan abolishes daylight saving time
. Kazakhstan Society in the UK (2005-03-21)
. Retrieved on 2007-03-28. </ref>//images.cell.com/images/EdImages/CurrentBiology/Kantermann.pdf |title= The human circadian clock's seasonal adjustment is disrupted by daylight saving time |author= Thomas Kantermann |coauthors= Myriam Juda; Martha Merrow; Till Roenneberg |accessdate=2007-10-27 |laysummary=http://abc.net.au/science/news/stories/2007/2070223.htm |laysource= ABC Science Online, Australia |laydate=2007-10-25}}</ref> The government of Kazakhstan cited health complications due to clock shifts as a primary reason for abolishing DST in 2005.<ref> Kazakhstan abolishes daylight saving time
. Kazakhstan Society in the UK (2005-03-21)
. Retrieved on 2007-03-28. </ref>
Complexity
www.recordcourier.com/apps/pbcs.dll/article?AID=/20031024/NEWS/310240104 |work= Record-Courier |date=2003-10-24 |accessdate=2007-10-29 |title= Daylight saving time ends Sunday |author= Joey Crandall}}</ref> People who work across time zone boundaries need to keep track of multiple DST rules, as not all locations observe DST or observe it the same way. The length of the day becomes variable. Disruption to meetings, travel, broadcasts, billing systems, and records management is common, and can be expensive.<ref> Paul McDougall
. " PG&E says patching meters for an early daylight-saving time will cost $38 million " , InformationWeek , 2007-03-01 . Retrieved on 2007-05-16 . </ref> Near an autumn transition from 02:00 to 01:00, a clock reads times from 01:00 to 02:00 twice, possibly leading to confusion.<ref> Daylight saving time: rationale and original idea . WebExhibits
. Retrieved on 2007-02-06. </ref>//www.recordcourier.com/apps/pbcs.dll/article?AID=/20031024/NEWS/310240104 |work= Record-Courier |date=2003-10-24 |accessdate=2007-10-29 |title= Daylight saving time ends Sunday |author= Joey Crandall}}</ref> People who work across time zone boundaries need to keep track of multiple DST rules, as not all locations observe DST or observe it the same way. The length of the day becomes variable. Disruption to meetings, travel, broadcasts, billing systems, and records management is common, and can be expensive.<ref> Paul McDougall
. " PG&E says patching meters for an early daylight-saving time will cost $38 million " , InformationWeek , 2007-03-01 . Retrieved on 2007-05-16 . </ref> Near an autumn transition from 02:00 to 01:00, a clock reads times from 01:00 to 02:00 twice, possibly leading to confusion.<ref> Daylight saving time: rationale and original idea . WebExhibits
. Retrieved on 2007-02-06. </ref>
www.csl.sri.com/users/neumann/cal.html#DatesTimes |isbn=0-201-55805-X |publisher=Addison-Wesley}} Retrieved on 2007-05-26.</ref> Medical devices may generate adverse events that could harm patients, without being obvious to clinicians responsible for care.<ref> Daniel G. Schultz
(2007-03-29) . Unpredictable events in medical equipment due to new daylight saving time change . Center for Devices and Radiological Health, Food and Drug Administration
. Retrieved on 2007-11-11. </ref> These problems are compounded when the DST rules themselves change, as in the Year 2007 problem. Software developers must test and perhaps modify many programs, and users must install updates and restart applications.<ref name='Tong'>Modèle:Cite journal</ref>//www.csl.sri.com/users/neumann/cal.html#DatesTimes |isbn=0-201-55805-X |publisher=Addison-Wesley}} Retrieved on 2007-05-26.</ref> Medical devices may generate adverse events that could harm patients, without being obvious to clinicians responsible for care.<ref> Daniel G. Schultz
(2007-03-29) . Unpredictable events in medical equipment due to new daylight saving time change . Center for Devices and Radiological Health, Food and Drug Administration
. Retrieved on 2007-11-11. </ref> These problems are compounded when the DST rules themselves change, as in the Year 2007 problem. Software developers must test and perhaps modify many programs, and users must install updates and restart applications.<ref name='Tong'>Modèle:Cite journal</ref>
www.squarefree.com/2006/11/01/continuous-daylight-saving-time/ |title= Continuous daylight saving time |work= Indistinguishable from Jesse |author= Jesse Ruderman |date=2006-11-01 |accessdate=2007-03-21}}</ref> or at least more gradually—for example, Willett originally suggested weekly 20-minute transitions—but this would add complexity and has never been implemented.//www.squarefree.com/2006/11/01/continuous-daylight-saving-time/ |title= Continuous daylight saving time |work= Indistinguishable from Jesse |author= Jesse Ruderman |date=2006-11-01 |accessdate=2007-03-21}}</ref> or at least more gradually—for example, Willett originally suggested weekly 20-minute transitions—but this would add complexity and has never been implemented.
www.santacruzsentinel.com/archive/2007/March/11/style/stories/01style.htm |accessdate=2007-05-16}}</ref> Also, DST complicates time-of-day approaches for avoiding sun exposure, necessitating even more the shadow rule of avoiding sun exposure whenever your shadow is shorter than you are.<ref>Modèle:Cite journal</ref>//www.santacruzsentinel.com/archive/2007/March/11/style/stories/01style.htm |accessdate=2007-05-16}}</ref> Also, DST complicates time-of-day approaches for avoiding sun exposure, necessitating even more the shadow rule of avoiding sun exposure whenever your shadow is shorter than you are.<ref>Modèle:Cite journal</ref>
Politics
www.winstonchurchill.org/i4a/pages/index.cfm?pageid=266 |accessdate=2007-05-16 |journal= Pictorial Weekly |date=1934-04-28}}</ref> Robertson Davies, however, detected "the bony, blue-fingered hand of Puritanism, eager to push people into bed earlier, and get them up earlier, to make them healthy, wealthy and wise in spite of themselves,"<ref>Modèle:Cite book</ref> and wags have dubbed it "Daylight Slaving Time"<ref>Modèle:Cite book</ref> or "Daylight Stupid Time".<ref> Diana M. Estill
. " On the clock " , Dallas Morning News , 2007-11-08 . Retrieved on 2007-11-11 . </ref> Historically, retailing, sports and tourism interests have favored daylight saving, while agricultural and evening entertainment interests have opposed it, and a war or economic crisis is often associated with its adoption.//www.winstonchurchill.org/i4a/pages/index.cfm?pageid=266 |accessdate=2007-05-16 |journal= Pictorial Weekly |date=1934-04-28}}</ref> Robertson Davies, however, detected "the bony, blue-fingered hand of Puritanism, eager to push people into bed earlier, and get them up earlier, to make them healthy, wealthy and wise in spite of themselves,"<ref>Modèle:Cite book</ref> and wags have dubbed it "Daylight Slaving Time"<ref>Modèle:Cite book</ref> or "Daylight Stupid Time".<ref> Diana M. Estill . " On the clock " , Dallas Morning News , 2007-11-08 . Retrieved on 2007-11-11 . </ref> Historically, retailing, sports and tourism interests have favored daylight saving, while agricultural and evening entertainment interests have opposed it, and a war or economic crisis is often associated with its adoption.
The fate of Willett's 1907 proposal illustrates several political issues involved. The proposal attracted many supporters, including Balfour, Churchill, Lloyd George, MacDonald, Edward VII (who used half-hour DST at Sandringham), the managing director of Harrods, and the manager of the National Bank. However, the opposition was stronger: it included Prime Minister Asquith, Christie (the Astronomer Royal), George Darwin, Napier Shaw (director of the Meteorological Office), many agricultural organizations, and theater owners. After many hearings the proposal was narrowly defeated in a Parliament committee vote in 1909. Willett's allies introduced similar bills every year from 1911 through 1914, to no avail.<ref>Modèle:Cite book</ref> The U.S. was even more skeptical: Andrew Peters introduced a DST bill to the U.S. House in May 1909, but it soon died in committee.<ref>Modèle:Cite book</ref>
World War I changed the political equation, as DST was promoted as a way to alleviate hardships from wartime coal shortages and air raid blackouts. After Germany led the way, the United Kingdom first used DST on May 21, 1916.<ref>Modèle:Cite book</ref> U.S. retailing and manufacturing interests led by Pittsburgh industrialist Robert Garland soon began lobbying for DST, but were opposed by railroads. The U.S.'s 1917 entry to the war overcame objections, and DST was established in 1918.<ref>Modèle:Cite book</ref>
www.srcf.ucam.org/~jsm28/british-time/ |accessdate=2007-10-24 |date=2007-09-16}}</ref> The U.S. was more typical: Congress repealed DST after 1919. President Woodrow Wilson, like Willett an avid golfer, vetoed the repeal twice but his second veto was overridden,<ref>Modèle:Cite book</ref> and only a few U.S. cities retained DST locally thereafter.<ref>Modèle:Cite book</ref> Wilson's successor Warren G. Harding opposed DST as a "deception". Reasoning that people should instead get up and go to work earlier in the summer, he ordered District of Columbia federal employees to start work at 08:00 rather than 09:00 during summer 1922. Many businesses followed suit though many others did not; the experiment was not repeated.<ref>Modèle:Cite book</ref>//www.srcf.ucam.org/~jsm28/british-time/ |accessdate=2007-10-24 |date=2007-09-16}}</ref> The U.S. was more typical: Congress repealed DST after 1919. President Woodrow Wilson, like Willett an avid golfer, vetoed the repeal twice but his second veto was overridden,<ref>Modèle:Cite book</ref> and only a few U.S. cities retained DST locally thereafter.<ref>Modèle:Cite book</ref> Wilson's successor Warren G. Harding opposed DST as a "deception". Reasoning that people should instead get up and go to work earlier in the summer, he ordered District of Columbia federal employees to start work at 08:00 rather than 09:00 during summer 1922. Many businesses followed suit though many others did not; the experiment was not repeated.<ref>Modèle:Cite book</ref>
commdocs.house.gov/committees/science/hsy73325.000/hsy73325_0.HTM |accessdate=2007-12-14}}</ref> in 2005, the Sporting Goods Manufacturers Association and the National Association of Convenience Stores successfully lobbied for the 2007 extension to U.S. DST.<ref name=Beam> Alex Beam
. " Dim-witted proposal for daylight time " , Boston Globe , 2005-07-26 . Retrieved on 2007-05-16 . </ref> In early 2007, Western Australia continued to debate a trial use of DST and several politicians changed positions after public sentiment swung against it.<ref> Joe Spagnolo . " High noon for sun-slingers " , Sunday Times , 2007-03-17 . Retrieved on 2007-05-16 . </ref> In the UK the sport and leisure industry supports a proposal to observe SDST's additional hour year-round.<ref> Single/Double Summer Time policy paper (PDF) . Royal Society for the Prevention of Accidents (Oct. 2006)
. Retrieved on 2007-05-16. </ref>//commdocs.house.gov/committees/science/hsy73325.000/hsy73325_0.HTM |accessdate=2007-12-14}}</ref> in 2005, the Sporting Goods Manufacturers Association and the National Association of Convenience Stores successfully lobbied for the 2007 extension to U.S. DST.<ref name=Beam> Alex Beam
. " Dim-witted proposal for daylight time " , Boston Globe , 2005-07-26 . Retrieved on 2007-05-16 . </ref> In early 2007, Western Australia continued to debate a trial use of DST and several politicians changed positions after public sentiment swung against it.<ref> Joe Spagnolo . " High noon for sun-slingers " , Sunday Times , 2007-03-17 . Retrieved on 2007-05-16 . </ref> In the UK the sport and leisure industry supports a proposal to observe SDST's additional hour year-round.<ref> Single/Double Summer Time policy paper (PDF) . Royal Society for the Prevention of Accidents (Oct. 2006)
. Retrieved on 2007-05-16. </ref>
Observance practices
In a typical case where a one-hour shift occurs at 02:00 local time, in spring the clock jumps forward from 02:00 standard time to 03:00 DST and the day has 23 hours, whereas in autumn the clock jumps backward from 02:00 DST to 01:00 standard time, repeating that hour, and the day has 25 hours. A digital display of local time does not read 02:00 exactly, but instead jumps from 01:59:59.9 either forward to 03:00:00.0 or backward to 01:00:00.0. In this example, a location observing [[UTC+10]] during standard time is at [[UTC+11]] during DST; conversely, a location at UTC−10 during standard time is at UTC−9 during DST.
www.lordhoweisland.info/flights.htm |publisher= Lord Howe Island Tourism Association |date=2007-12-12 |accessdate=2007-12-14}}</ref> Twenty-minute and two-hour shifts have been used in the past.//www.lordhoweisland.info/flights.htm |publisher= Lord Howe Island Tourism Association |date=2007-12-12 |accessdate=2007-12-14}}</ref> Twenty-minute and two-hour shifts have been used in the past.
www.bom.gov.au/climate/averages/tables/dst_times.shtml |title= Implementation dates of daylight saving time within Australia |publisher= Bureau of Meteorology |date=2007-10-30 |accessdate=2007-11-06}}</ref>//www.bom.gov.au/climate/averages/tables/dst_times.shtml |title= Implementation dates of daylight saving time within Australia |publisher= Bureau of Meteorology |date=2007-10-30 |accessdate=2007-11-06}}</ref>
www.timesonline.co.uk/tol/news/world/us_and_americas/article1499835.ece |accessdate=2007-05-16 |title= US gets summertime blues as the clocks go forward 3 weeks early |work= The Times}}</ref> The 2007 U.S. change was part of the Energy Policy Act of 2005; previously, from 1987 through 2006, the start and end dates were the first Sunday in April and the last Sunday in October, and Congress retains the right to go back to the previous dates once an energy-consumption study is done.<ref> Energy Policy Act of 2005, Public Law 109-58 § 110
(2005-08-08)
. Retrieved on 2007-05-10. </ref>//www.timesonline.co.uk/tol/news/world/us_and_americas/article1499835.ece |accessdate=2007-05-16 |title= US gets summertime blues as the clocks go forward 3 weeks early |work= The Times}}</ref> The 2007 U.S. change was part of the Energy Policy Act of 2005; previously, from 1987 through 2006, the start and end dates were the first Sunday in April and the last Sunday in October, and Congress retains the right to go back to the previous dates once an energy-consumption study is done.<ref> Energy Policy Act of 2005, Public Law 109-58 § 110
(2005-08-08)
. Retrieved on 2007-05-10. </ref>
www.horaoficial.cl/horaof.htm}}</ref> The time difference between the United Kingdom and mainland Chile may therefore be three, four, or five hours, depending on the time of year.//www.horaoficial.cl/horaof.htm}}</ref> The time difference between the United Kingdom and mainland Chile may therefore be three, four, or five hours, depending on the time of year.
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inms-ienm.nrc-cnrc.gc.ca/time_services/daylight_saving_e.html |date=2007-05-05 |accessdate=2007-05-10 |publisher= Institute for National Measurement Standards}}</ref> The United Kingdom and Ireland experimented with year-round DST from 1968 to 1971 but abandoned it because of its unpopularity, particularly in northern regions.<ref> Philip Johnston
. " Is it time to lighten our darkness? " , Daily Telegraph , 2007-01-22 . Retrieved on 2007-05-16 . </ref>//inms-ienm.nrc-cnrc.gc.ca/time_services/daylight_saving_e.html |date=2007-05-05 |accessdate=2007-05-10 |publisher= Institute for National Measurement Standards}}</ref> The United Kingdom and Ireland experimented with year-round DST from 1968 to 1971 but abandoned it because of its unpopularity, particularly in northern regions.<ref> Philip Johnston . " Is it time to lighten our darkness? " , Daily Telegraph , 2007-01-22 . Retrieved on 2007-05-16 . </ref>
www.farnorthscience.com/2007/03/11/news-from-alaska/alaska-daylight-stealing-time/ |date=2007-04-01 |accessdate=2007-12-14}}</ref>//www.farnorthscience.com/2007/03/11/news-from-alaska/alaska-daylight-stealing-time/ |date=2007-04-01 |accessdate=2007-12-14}}</ref>
pcdsh01.on.br/DecHV.html |accessdate=2007-11-06 |date=2007 |language=Portuguese |publisher= Time Service Dept., National Observatory, Brazil}}</ref> Only a minority of the world's population uses DST because Asia and Africa generally do not observe it.//pcdsh01.on.br/DecHV.html |accessdate=2007-11-06 |date=2007 |language=Portuguese |publisher= Time Service Dept., National Observatory, Brazil}}</ref> Only a minority of the world's population uses DST because Asia and Africa generally do not observe it.
Terminology
www.bartleby.com/61/65/D0046500.html|editor=Joseph P. Pickett et al.|title=The American Heritage Dictionary of the English Language|edition=4th ed. (2000)|publisher=Houghton Mifflin|location=Boston|isbn=0-395-82517-2|quote=variant forms: or daylight-savings time}} Retrieved on 2007-05-26. | daylight saving time
. Merriam-Webster's Online Dictionary
. Retrieved on 2007-03-08.
“called also daylight saving, daylight savings, daylight savings time, daylight time” | 15 U.S.C. § 260a notes
. Retrieved on 2007-05-09.
“Congressional Findings; Expansion of Daylight Saving Time”
</ref>//www.bartleby.com/61/65/D0046500.html|editor=Joseph P. Pickett et al.|title=The American Heritage Dictionary of the English Language|edition=4th ed. (2000)|publisher=Houghton Mifflin|location=Boston|isbn=0-395-82517-2|quote=variant forms: or daylight-savings time}} Retrieved on 2007-05-26. | daylight saving time
. Merriam-Webster's Online Dictionary
. Retrieved on 2007-03-08.
“called also daylight saving, daylight savings, daylight savings time, daylight time” | 15 U.S.C. § 260a notes
. Retrieved on 2007-05-09.
“Congressional Findings; Expansion of Daylight Saving Time”
</ref>
Time zone names typically change when DST is observed. American English replaces standard with daylight: for example, Pacific Standard Time (PST) becomes Pacific Daylight Time (PDT). British English uses summer: for example, Greenwich Mean Time (GMT) becomes British Summer Time (BST). Abbreviations do not always change: for example, many (though not all) Australians say that Eastern Standard Time (EST) becomes Eastern Summer Time (also EST).
www.languagerealm.com/langarticles/time_talk.php |work= Language Realm |accessdate=2007-10-24 |date=2007}}</ref> works only in the northern hemisphere, and is less robust against future rule changes.//www.languagerealm.com/langarticles/time_talk.php |work= Language Realm |accessdate=2007-10-24 |date=2007}}</ref> works only in the northern hemisphere, and is less robust against future rule changes.
Computing
Many computer-based systems can shift their clocks automatically when DST starts and finishes, based on their time zone settings. Two implementations in wide use today are zoneinfo and Microsoft Windows.
Zoneinfo
www.twinsun.com/tz/tz-link.htm |title= Sources for time zone and daylight saving time data |date=2007-11-29 |accessdate=2007-12-14}}</ref> HP's "tztab" database is similar but incompatible.<ref> tztab(4)
. HP-UX Reference: HP-UX 11i Version 3 . Hewlett-Packard Co. (2007)
. Retrieved on 2007-05-16.
</ref> When temporal authorities change DST rules, zoneinfo updates are installed as part of ordinary system maintenance. In Unix-like systems a process's TZ environment variable specifies the location name, as in TZ='America/New_York'.//www.twinsun.com/tz/tz-link.htm |title= Sources for time zone and daylight saving time data |date=2007-11-29 |accessdate=2007-12-14}}</ref> HP's "tztab" database is similar but incompatible.<ref> tztab(4)
. HP-UX Reference: HP-UX 11i Version 3 . Hewlett-Packard Co. (2007)
. Retrieved on 2007-05-16.
</ref> When temporal authorities change DST rules, zoneinfo updates are installed as part of ordinary system maintenance. In Unix-like systems a process's TZ environment variable specifies the location name, as in TZ='America/New_York'.
www.unix.org/version3/|accessdate=2007-05-16|publisher=The Open Group|work=IEEE Std 1003.1-2004|date=2004|url=http://www.opengroup.org/susv3/basedefs/xbd_chap08.html#tag_08_03|title=Other environment variables}}</ref>//www.unix.org/version3/|accessdate=2007-05-16|publisher=The Open Group|work=IEEE Std 1003.1-2004|date=2004|url=http://www.opengroup.org/susv3/basedefs/xbd_chap08.html#tag_08_03|title=Other environment variables}}</ref>
Microsoft Windows
support.microsoft.com/gp/cp_dst |title= Daylight saving time help and support center |publisher= Microsoft Corp. |date=2007-09-14 |accessdate=2007-10-24}}</ref> Windows Vista supports at most two start and end rules per time zone setting. In a Canadian location observing DST, a single Vista setting supports both 1987–2006 and post-2006 time stamps, but mishandles some older time stamps. Older Microsoft Windows systems usually store only a single start and end rule for each zone, so that the same Canadian setting reliably supports only post-2006 time stamps.<ref> Visual Studio and daylight saving time change
. Microsoft Corp. (2007)
. Retrieved on 2007-03-22. </ref>//support.microsoft.com/gp/cp_dst |title= Daylight saving time help and support center |publisher= Microsoft Corp. |date=2007-09-14 |accessdate=2007-10-24}}</ref> Windows Vista supports at most two start and end rules per time zone setting. In a Canadian location observing DST, a single Vista setting supports both 1987–2006 and post-2006 time stamps, but mishandles some older time stamps. Older Microsoft Windows systems usually store only a single start and end rule for each zone, so that the same Canadian setting reliably supports only post-2006 time stamps.<ref> Visual Studio and daylight saving time change
. Microsoft Corp. (2007)
. Retrieved on 2007-03-22. </ref>
lingnu.com/support.html#timezone |title= Windows daylight savings timezones for Israel |publisher= Lingnu Open Source Consulting |date=2005-04-20 |accessdate=2007-03-22}}</ref> and a Microsoft tool that switches zones automatically.<ref> Microsoft support entry regarding daylight saving time in Israel
(Hebrew)
. Microsoft Corp.
(2007)
. Retrieved on 2007-03-22. </ref>//lingnu.com/support.html#timezone |title= Windows daylight savings timezones for Israel |publisher= Lingnu Open Source Consulting |date=2005-04-20 |accessdate=2007-03-22}}</ref> and a Microsoft tool that switches zones automatically.<ref> Microsoft support entry regarding daylight saving time in Israel
(Hebrew)
. Microsoft Corp.
(2007)
. Retrieved on 2007-03-22. </ref>
References
Further reading
www.shoemakerhoard.com/catalog/spring.html|accessdate=2007-05-16|title=Spring Forward: The Annual Madness of Daylight Saving Time|publisher=Shoemaker & Hoard|date=2005|isbn=1-59376-053-1}}//www.shoemakerhoard.com/catalog/spring.html|accessdate=2007-05-16|title=Spring Forward: The Annual Madness of Daylight Saving Time|publisher=Shoemaker & Hoard|date=2005|isbn=1-59376-053-1}} www.seizethedaylight.com/|title=Seize the Daylight: The Curious and Contentious Story of Daylight Saving Time|accessdate=2007-05-16|publisher=Thunder’s Mouth Press|date=2005|isbn=1-56025-655-9}} The British version, focusing on the UK, is Modèle:Cite book//www.seizethedaylight.com/|title=Seize the Daylight: The Curious and Contentious Story of Daylight Saving Time|accessdate=2007-05-16|publisher=Thunder’s Mouth Press|date=2005|isbn=1-56025-655-9}} The British version, focusing on the UK, is Modèle:Cite book
External links
www.webexhibits.org/daylightsaving/ Daylight Saving Time] - general history and anecdotes//www.webexhibits.org/daylightsaving/ Daylight Saving Time] - general history and anecdotes www.webexhibits.org/daylightsaving/ Daylight Saving Time] - general history and anecdotes//www.energy.ca.gov/daylightsaving.html Saving Time, Saving Energy] - North American viewpoint www.webexhibits.org/daylightsaving/ Daylight Saving Time] - general history and anecdotes//www.merlyn.demon.co.uk/uksumtim.htm Summer Time] - European viewpoint www.webexhibits.org/daylightsaving/ Daylight Saving Time] - general history and anecdotes//www.twinsun.com/tz/tz-link.htm Sources for time zone and daylight saving time data] - technical resources
Modèle:Featured articleModèle:Link FA
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