Daylight saving time: Difference between revisions
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Adding daylight to afternoons generally benefits retailing, sports, and other activities that exploit sunlight after working hours,<ref name='Benfield'/> but it can cause problems for farmers and others whose hours depend on the sun.<ref name='Star'/> Extra afternoon daylight appears to cut traffic fatalities;<ref name='Ferguson'/> its effect on health and crime is less clear. An early goal was to reduce evening usage of [[incandescent lighting]], formerly a primary use of electricity;<ref name='Lawson'/> nowadays, though, DST sometimes increases overall electricity costs and peak demand.<ref name='Kellogg'/> |
Adding daylight to afternoons generally benefits retailing, sports, and other activities that exploit sunlight after working hours,<ref name='Benfield'/> but it can cause problems for farmers and others whose hours depend on the sun.<ref name='Star'/> Extra afternoon daylight appears to cut traffic fatalities;<ref name='Ferguson'/> its effect on health and crime is less clear. An early goal was to reduce evening usage of [[incandescent lighting]], formerly a primary use of electricity;<ref name='Lawson'/> nowadays, though, DST sometimes increases overall electricity costs and peak demand.<ref name='Kellogg'/> |
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DST's clock shifts complicate timekeeping and can disrupt meetings, travel, billing, recordkeeping, medical devices, and heavy equipment;<ref name=Neumann/> |
DST's clock shifts 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/> |
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==Origin== |
==Origin== |
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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>{{cite book|author=House Committee on Energy and Commerce, Subcommittee on Energy Conservation and Power|title=Daylight saving time|date=[[1985-04-24]]|series=Serial No. 99-4|publisher=[[United States Government Printing Office|U.S. GPO]]|pages=26}}</ref> Outdoor lighting has a marginal and sometimes even contradictory influence on crime and fear of crime.<ref>{{cite journal |journal= Environment and Planning A |volume=38 |issue=11 |pages=2055–2074 |author= Rachel Pain |coauthors= Robert MacFarlane; Keith Turner; Sally Gill |title= 'When, where, if, and but': qualifying GIS and the effect of streetlighting on crime and fear |doi=10.1068/a38391}}</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>{{cite book|author=House Committee on Energy and Commerce, Subcommittee on Energy Conservation and Power|title=Daylight saving time|date=[[1985-04-24]]|series=Serial No. 99-4|publisher=[[United States Government Printing Office|U.S. GPO]]|pages=26}}</ref> Outdoor lighting has a marginal and sometimes even contradictory influence on crime and fear of crime.<ref>{{cite journal |journal= Environment and Planning A |volume=38 |issue=11 |pages=2055–2074 |author= Rachel Pain |coauthors= Robert MacFarlane; Keith Turner; Sally Gill |title= 'When, where, if, and but': qualifying GIS and the effect of streetlighting on crime and fear |doi=10.1068/a38391}}</ref> |
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In several countries, [[fire safety]] officials encourage citizens to use the two annual clock shifts as reminders to replace batteries in [[Smoke detector|smoke]] and [[carbon monoxide detector]]s. This is especially important in autumn, just before the [[HVAC|heating]] and candle season causes an increase in home fires. Similar twice-yearly tasks include reviewing and practicing fire escape and family disaster plans, inspecting vehicle lights, checking storage areas for hazardous materials, and reprogramming [[thermostat]]s.<ref>{{cite news |title= Changes to daylight-saving time |author= Helen A.S. Popkin |work= Consumer Reports Home & Yard Blog |date=[[2007-03-02]] |url=http://blogs.consumerreports.org/home/2007/03/changes_to_dayl.html |accessdate=2007-11-02}}</ref><ref>{{cite press release|title=A timely day to check your smoke alarm|publisher=New Zealand Fire Service|url=http://www.fire.org.nz/news/media/2002/2002-03-13-1.htm|accessdate=2007-05-15|date=[[2002-03-13]]}}</ref><ref name='USFA'>{{cite press release|url=http://www.cpsc.gov/cpscpub/prerel/prhtml07/07124.html|accessdate=2007-05-16|title=CSPC and USFA encourage consumers to spring forward with fire safety in mind|date=[[2007-03-09]]|publisher=U.S. Consumer Product Safety Commission; U.S. Fire Administration}}</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>{{cite web|title=Prevent household fires|url=http://health.yahoo.com/topic/children/resources/article/healthwise/ue5167|accessdate=2007-05-16|date=2005-04-08|author=Amy Fackler|work=Yahoo Health}}</ref> |
In several countries, [[fire safety]] officials encourage citizens to use the two annual clock shifts as reminders to replace batteries in [[Smoke detector|smoke]] and [[carbon monoxide detector]]s<ref name=USFA/>. This is especially important in autumn, just before the [[HVAC|heating]] and candle season causes an increase in home fires. Similar twice-yearly tasks include reviewing and practicing fire escape and family disaster plans, inspecting vehicle lights, checking storage areas for hazardous materials, and reprogramming [[thermostat]]s.<ref>{{cite news |title= Changes to daylight-saving time |author= Helen A.S. Popkin |work= Consumer Reports Home & Yard Blog |date=[[2007-03-02]] |url=http://blogs.consumerreports.org/home/2007/03/changes_to_dayl.html |accessdate=2007-11-02}}</ref><ref>{{cite press release|title=A timely day to check your smoke alarm|publisher=New Zealand Fire Service|url=http://www.fire.org.nz/news/media/2002/2002-03-13-1.htm|accessdate=2007-05-15|date=[[2002-03-13]]}}</ref><ref name='USFA'>{{cite press release|url=http://www.cpsc.gov/cpscpub/prerel/prhtml07/07124.html|accessdate=2007-05-16|title=CSPC and USFA encourage consumers to spring forward with fire safety in mind|date=[[2007-03-09]]|publisher=U.S. Consumer Product Safety Commission; U.S. Fire Administration}}</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>{{cite web|title=Prevent household fires|url=http://health.yahoo.com/topic/children/resources/article/healthwise/ue5167|accessdate=2007-05-16|date=2005-04-08|author=Amy Fackler|work=Yahoo Health}}</ref> |
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===Health=== |
===Health=== |
Revision as of 08:48, 8 November 2007
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. Despite controversy, many countries have used it since then; details vary by location and change occasionally.
Adding daylight to afternoons generally benefits retailing, sports, and other activities that exploit sunlight after working hours,[1] but it can cause problems for farmers and others whose hours depend on the sun.[2] Extra afternoon daylight appears to cut traffic fatalities;[3] its effect on health and crime is less clear. An early goal was to reduce evening usage of incandescent lighting, formerly a primary use of electricity;[4] nowadays, though, DST sometimes increases overall electricity costs and peak demand.[5]
DST's clock shifts complicate timekeeping and can disrupt meetings, travel, billing, recordkeeping, medical devices, and heavy equipment;[6]. Many computer-based systems can adjust their clocks automatically, but this can be limited and error-prone, particularly when DST rules change.[7]
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.[8] 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.[9] 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.[10]
During his time as an American envoy to France, Benjamin Franklin anonymously published a letter in 1784 suggesting that Parisians economize on candles by arising earlier to use morning sunlight.[11] Franklin's satire proposed taxing shutters, rationing candles, and waking the public by ringing church bells and firing cannons at sunrise, in the spirit of his earlier proverb "Early to bed and early to rise / Makes a man healthy, wealthy, and wise."[12] Franklin did not propose shifting clocks; 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.[13]
In 1905, the prominent English builder and outdoorsman William Willett was inspired to invent DST during one of his pre-breakfast horseback rides, when he observed with dismay how many Londoners slept through the best part of a summer day.[15] 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.[16] 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, but 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.[17]
Benefits and drawbacks
Willett's 1907 proposal argued that DST increases opportunities for outdoor leisure activities during afternoon sunlight hours. Obviously it does not change the length of the day; the longer days nearer the summer solstice in high latitudes merely offer more room to shift apparent daylight from morning to evening so that early morning daylight is not wasted.[16]
However, many people ignore DST by altering their nominal work schedules to coordinate with daylight, television broadcasts, or remote colleagues.[18] DST is commonly not observed during most of winter, because its mornings are darker: workers may have no sunlit leisure time, and children may need to leave for school in the dark.[19]
Energy use
Delaying the nominal time of sunrise and sunset increases the use of artificial light in the morning and reduces it in the evening. As Franklin's 1784 satire pointed out, energy is conserved if the evening reduction outweighs the morning increase, which can happen if more people need evening light than morning. An early goal of DST was to reduce evening usage of incandescent lighting, formerly a primary use of electricity.[4] However, statistically significant evidence for energy conservation 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,[4] but the National Bureau of Standards (NBS) reviewed the DOT study in 1976 and found no significant energy savings.[19] 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.[5] A 2007 simulation estimated that introducing DST to Japan would increase 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; the simulation did not examine non-residential buildings.[20] In North America, there was no clear evidence that electricity would be saved by the extra DST introduced in 2007,[21] and although one utility did report a decrease in March 2007, five others did not.[22] DST may increase gasoline consumption: U.S. gasoline demand grew an extra 1% during the newly introduced DST in March 2007.[23]
Economic effects
Retailers, sporting goods makers, and other businesses benefit from extra afternoon sunlight, as it induces customers to shop and to participate in outdoor afternoon sports. For example, in 1984 Fortune magazine estimated that a seven-week extension of DST would yield an additional $30 million for 7-Eleven stores, and the National Golf Foundation estimated the extension would increase golf industry revenues $200 million to $300 million.[25] Conversely, DST can adversely affect farmers and others whose hours are set by the sun. For example, grain harvesting is best done after dew evaporates, so when field hands arrive and leave earlier in summer their labor is less valuable.[2] DST also hurts prime-time broadcast ratings[26] and theaters, especially drive-ins.[27]
Clock shifts correlate with decreased economic efficiency. In 2000 the daylight-saving effect implied an estimated one-day loss of $31 billion on U.S. stock exchanges.[28] Clock shifts and DST rule changes have a direct economic cost, since they entail extra work to support remote meetings, computer applications and the like. For example, a 2007 North American rule change cost an estimated $500 million to $1 billion.[29]
Public safety
In 1975 the U.S. DOT conservatively identified a 0.7% reduction in traffic fatalities during DST, and estimated the real reduction to be 1.5% to 2%,[4] but the 1976 NBS review of the DOT study found no differences in traffic fatalities.[19] In 1995 the Insurance Institute for Highway Safety estimated a reduction of 1.2%, including a 5% reduction in crashes fatal to pedestrians.[3] Others have found similar reductions.[30] 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.[31] It is not clear whether sleep disruption contributes to fatal accidents immediately after the spring and autumn clock shifts. 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.[32][33]
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."[34] Outdoor lighting has a marginal and sometimes even contradictory influence on crime and fear of crime.[35]
In several countries, fire safety officials encourage citizens to use the two annual clock shifts as reminders to replace batteries in smoke and carbon monoxide detectors[36]. This is especially important in autumn, just before the heating and candle season causes an increase in home fires. Similar twice-yearly tasks include reviewing and practicing fire escape and family disaster plans, inspecting vehicle lights, checking storage areas for hazardous materials, and reprogramming thermostats.[37][38][36] This is not an essential function of DST, as locations without DST can instead use the first days of spring and autumn as reminders.[39]
Health
DST has mixed effects on health. In societies with fixed work schedules it provides more afternoon sunlight for outdoor exercise, which can contribute greatly to health. It alters sunlight exposure; whether this is beneficial depends on one's location and daily schedule, as sunlight triggers vitamin D synthesis in the skin, but overexposure can lead to skin cancer. Sunlight strongly influences seasonal affective disorder; DST may help in depression by causing individuals to arise earlier,[40] but some argue the reverse.[41] The Retinitis Pigmentosa Foundation Fighting Blindness, chaired by blind sports magnate Gordon Gund, successfully lobbied in 1985 and 2005 for U.S. DST extensions,[1][42] but DST can hurt night blindness sufferers.[43]
Clock shifts reduce sleep duration and efficiency,[44] particularly for late-risers after clocks spring forward; effects can last for weeks.[45] The government of Kazakhstan cited health complications due to clock shifts as a primary reason for abolishing DST in 2005.[46]
Complexity
DST's clock shifts have the obvious disadvantage of complexity. People must remember to change their clocks; this consumes time, particularly for mechanical clocks that cannot be moved backward safely.[47] 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.[48] 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.[49]
Computer-based systems may also require downtime or restarting when clocks shift. Ignoring this requirement damaged a German steel facility in 1993.[6] Medical devices may generate adverse events that could harm patients, without being obvious to clinicians responsible for care.[50] 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.[7]
Some clock-shift problems could be avoided by adjusting clocks continuously[51] or at least more gradually—for example, Willett originally suggested weekly 20-minute transitions—but this would add complexity and has never been implemented.
DST inherits and can magnify the disadvantages of standard time. For example, when reading a sundial, one must compensate for it along with time zone and natural discrepancies.[52] 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.[53]
Politics
Daylight saving has caused controversy since it began. Winston Churchill argued that it enlarges "the opportunities for the pursuit of health and happiness among the millions of people who live in this country".[54] 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."[55] 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.[56] The U.S. was even more skeptical: U.S. Representative Andrew Peters of Massachusetts introduced a DST bill in May 1909, but it soon died in committee.[57]
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.[58] 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.[59]
War's end swung the pendulum back. Farmers continued to dislike DST, and many countries repealed it after the war. Britain was an exception: it retained DST nationwide but over the years adjusted transition dates for several reasons, including special rules during the 1920s and 1930s to avoid clock shifts on Easter mornings.[60] 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,[61] and only a few U.S. cities retained DST locally thereafter.[62]
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, and critics gave the scheduling mess names like "Ragtime" and "Daylight Slaving Time"; the experiment was not repeated.[63] More recent economic theory suggests that general agreement about the day's layout confers so many advantages that a standard DST schedule usually outranks ad hoc efforts to get up earlier, even for people who personally dislike the DST schedule.[64]
Since Willett's day the world has seen many enactments, adjustments, and repeals of DST, with similar politics involved.[65] The U.S. advanced clocks by an hour throughout World War II,[66] but it was not until 1966 that the federal government established peacetime DST, except for a few locations like Hawaii.[67] In the mid-1980s, Clorox (parent of Kingsford Charcoal) and 7-Eleven provided the primary funding for the Daylight Saving Time Coalition behind the 1987 extension to U.S. DST, and both Idaho senators voted for it on the basis of fast-food restaurants selling more French fries made from Idaho potatoes;[1] in 2005, the Sporting Goods Manufacturers Association and the National Association of Convenience Stores successfully lobbied for the 2007 extension to U.S. DST.[42] In early 2007, Western Australia continued to debate a trial use of DST and several politicians changed positions after public sentiment swung against it.[68] In the UK the sport and leisure industry supports a proposal to observe SDST's additional hour year-round.[69]
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.
Clock shifts are usually scheduled near a weekend midnight to lessen disruption to weekday schedules. A one-hour shift is customary, but Australia's Lord Howe Island uses a half-hour shift.[70] Twenty-minute and two-hour shifts have been used in the past.
Coordination strategies differ when adjacent time zones shift clocks. The European Union shifts all at once, at 01:00 UTC; for example, Eastern European Time is always one hour ahead of Central European Time.[60] Most of North America shifts at 02:00 local time, so its zones do not shift at the same time; for example, Mountain Time can be temporarily either zero or two hours ahead of Pacific Time. Australian districts go even further and do not always agree on start and end dates; for example, to start DST in 2006 Tasmania shifted clocks forward on 1 October, Western Australia on 3 December, and the remaining DST-observing areas on 29 October.[71]
Start and end dates vary with location and year. Since 1996 European Summer Time has been observed from the last Sunday in March to the last Sunday in October; previously the rules were not uniform across the European Union.[60] Starting in 2007, most of the United States and Canada observe DST from the second Sunday in March to the first Sunday in November, about two-thirds of the year.[72] 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.[73]
Beginning and ending dates are the reverse in the southern hemisphere. For example, mainland Chile observes DST from the second Saturday in October to the second Saturday in March, with transitions at 24:00 local time.[74] The time difference between the United Kingdom and mainland Chile may therefore be three, four, or five hours, depending on the time of year.
Argentina, western China, Iceland, and other areas skew time zones westward, in effect observing DST year round without complications from clock shifts. For example, Saskatoon, Saskatchewan is at 106°39′W longitude, slightly west of center of the idealized Mountain Time Zone (105°W), but Saskatchewan observes Central Standard Time (90°W) year-round so Saskatoon is always about 67 minutes ahead of mean solar time.[75] 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.[76]
Western France, Spain, and other areas skew time zones and shift clocks, in effect observing DST in winter with an extra hour in summer. For example, Nome, Alaska is at 165°24′W longitude, which is just west of center of the idealized Samoa Time Zone (165°W), but Nome observes Alaska Time (135°W) with DST, so it is slightly more than two hours ahead of the sun in winter and three in summer.[77]
DST is generally not observed near the equator, where sunrise times do not vary enough to justify it. Some countries observe it only in some regions; for example, southern Brazil observes it while equatorial Brazil does not.[78] Only a minority of the world's population uses DST because Asia and Africa generally do not observe it.
Terminology
In the normative form, daylight saving time uses the present participle saving as an adjective, as in labor saving device; the first two words are sometimes hyphenated. Daylight savings time and daylight time are common variants.[79]
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, Central European Time (CET) becomes Central European Summer Time (CEST). Abbreviations do not always change: for example, many (though not all) Australians say that Eastern Standard Time (EST) becomes Eastern Summer Time (also EST).
The American English mnemonic "spring forward, fall back" (also "spring ahead …", "spring up …", and "… fall behind") helps people remember which direction to shift clocks. Much of North America now advances clocks before the vernal equinox, so the mnemonic disagrees with the astronomical definition of spring, but a proposed substitute "March forward …"[80] 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
The zoneinfo database maps a name to the named location's historical and predicted clock shifts. This database is used by many computer software systems, including most Unix-like operating systems, Java, and Oracle;[81] HP's "tztab" database is similar but incompatible.[82] 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'
.
Older or stripped-down systems may support only the TZ values required by POSIX, which specify at most one start and end rule explicitly in the value. For example, TZ='EST5EDT,M3.2.0/02:00,M11.1.0/02:00'
specifies time for eastern North America starting in 2007. TZ must be changed whenever DST rules change, and the new TZ value applies to all years, mishandling some older time stamps.[83]
Microsoft Windows
As with zoneinfo, a user of Microsoft Windows configures DST by specifying the name of a location, and the operating system then consults a table of rule sets that must be updated when DST rules change. Procedures for specifying the name and updating the table vary with release. Updates are not issued for older versions of Microsoft Windows.[84] 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.[85]
These limitations have caused problems. For example, before 2005, DST in Israel varied each year and was skipped some years. Windows 95 used rules correct for 1995 only, causing problems in later years. In Windows 98 Microsoft gave up and marked Israel as not having DST, forcing Israeli users to shift their computer clocks manually twice a year. The 2005 Israeli Daylight Saving Law established predictable rules but Windows zone files cannot represent the rules' dates in a year-independent way. Partial workarounds, which mishandle older time stamps, include manually switching zone files every year[86] and a Microsoft tool that switches zones automatically.[87]
Notes
- ^ a b c James C. Benfield (2001-05-24). "Statement to the U.S. House, Committee on Science, Subcommittee on Energy". Energy Conservation Potential of Extended and Double Daylight Saving Time. Serial 107-30. Retrieved 2007-05-16.
{{cite book}}
: Check date values in:|date=
(help) - ^ a b "Daylight savings time". Session Weekly. Minnesota House Public Information Office. 1991. Retrieved 2003-03-21.
… 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." '
- ^ a b Susan A. Ferguson (1995). "Daylight saving time and motor vehicle crashes: the reduction in pedestrian and vehicle occupant fatalities". American Journal of Public Health. 85 (1). American Public Health Association: 92–95. PMID 7832269. Retrieved 2007-07-14.
{{cite journal}}
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suggested) (help) - ^ a b c d Linda L. Lawson (2001-05-24). "Statement to the U.S. House, Committee on Science, Subcommittee on Energy". Energy Conservation Potential of Extended and Double Daylight Saving Time. Serial 107-30. Retrieved 2007-05-16.
{{cite book}}
: Check date values in:|date=
(help) - ^ a b Ryan Kellogg; Hendrik Wolff (2007). "Does extending daylight saving time save energy? Evidence from an Australian experiment". CSEMWP 163. Center for the Study of Energy Markets. Retrieved 2007-05-16.
{{cite journal}}
: Cite journal requires|journal=
(help)CS1 maint: multiple names: authors list (link) - ^ a b Peter G. Neumann (1994). "Computer date and time problems". Computer-Related Risks. Addison-Wesley. ISBN 0-201-55805-X.
{{cite book}}
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|chapterurl=
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suggested) (help) Retrieved on 2007-05-26. - ^ a b Stephen Tong (2007). "Are you prepared for daylight saving time in 2007?". IT Professional. 9 (1). IEEE Computer Society: 36–41. Retrieved 2007-05-16.
{{cite journal}}
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suggested) (help) - ^ B.L. Ullman (1918). "Daylight saving in ancient Rome". The Classical Journal. 13 (6): 450–451.
- ^ Jérôme Carcopino (1968). "The days and hours of the Roman calendar". Daily Life in Ancient Rome: The People and the City at the Height of the Empire. Yale University Press. ISBN 0300000316.
- ^ Robert Kaplan (2003). "The holy mountain". Atlantic. 292 (5): 138–141.
- ^ a b Benjamin Franklin, writing anonymously (1784-04-26). "Aux auteurs du Journal". Journal de Paris (in French) (117).
{{cite journal}}
: Check date values in:|date=
(help) 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 A.O. Aldridge (1956). "Franklin's essay on daylight saving". American Literature. 28 (1): 23–29. - ^ Seymour Stanton Block (2006). "Benjamin Franklin: America's inventor". American History. Retrieved 2007-02-16.
- ^ Eviatar Zerubavel (1982). "The standardization of time: a sociohistorical perspective". The American Journal of Sociology. 88 (1): 1–23.
- ^ Prerau. Seize the Daylight. p. 22.
- ^ David Rooney (2007). "Royal Observatory commemorates William Willett". Petts Wood & District Residents' Association. Retrieved 2007-03-27.
- ^ a b c William Willett (1907). "The waste of daylight". 1st edition. Retrieved 2007-05-16.
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(help) | William Willett (1914). "The waste of daylight" (PDF). 19th edition. Retrieved 2007-05-16.{{cite journal}}
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(help) - ^ Prerau. Seize the Daylight. pp. 51–89.
- ^ Daniel S. Hamermesh; Caitlin Knowles Myers; Mark L. Pocock (2006). "Time zones as cues for coordination: latitude, longitude, and Letterman". Working Paper No. W12350. National Bureau of Economic Research.
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(help)CS1 maint: multiple names: authors list (link) SSRN 913313. - ^ a b c Mark Gurevitz (2006-04-04). "Daylight saving time". Order Code RS22284. Congressional Research Service. Retrieved 2007-06-01.
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(help) - ^ Yoshiyuki Shimoda (2007). "Evaluation of city-scale impact of residential energy conservation measures using the detailed end-use simulation model". Energy. 32 (9): 1617–1633. doi:10.1016/j.energy.2007.01.007.
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(help) - ^ Cindy Cline (2007-03-21). "Early daylight saving time hasn't saved energy in Ottawa". CFRA. Retrieved 2007-05-16.
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(help) | Jim Goddard (2007-04-02). "No saving to hydro and gas bill with earlier time change". News1130. Retrieved 2007-05-16.{{cite news}}
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(help) | Lisa Lee (2007-04-02). "Early U.S. Daylight Savings a bust in power savings". Reuters. Retrieved 2007-05-16.{{cite news}}
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(help) | "Daylight saving time reduces power consumption". AM770CHQR. 2007-04-03. Retrieved 2007-05-16.{{cite news}}
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(help) | Ned Potter (2007-04-04). "Final word on daylight saving—not". ABC News. Retrieved 2007-05-16.{{cite news}}
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(help) - ^ Shawn McCarthy (2007-04-18). "Has daylight saving time fuelled gasoline consumption?". The Globe and Mail.
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(help) - ^ Sualeh Fatehi (2007-05-15). "Daylight Chart". SourceForge.net. Retrieved 2007-06-25.
- ^ Downing. Spring Forward. pp. 147–148.
- ^ Rick Kissell (2007-03-20). "Daylight-saving dock ratings". Variety. Retrieved 2007-05-16.
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(help) - ^ Todd D. Rakoff (2002). A Time for Every Purpose: Law and the Balance of Life. Harvard University Press. p. 26. ISBN 067400910X.
- ^ Mark J. Kamstra (2000). "Losing sleep at the market: the daylight saving anomaly". The American Economic Review. 90 (4): 1005–1011.
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suggested) (help) - ^ Ben Arnoldy (2007-03-07). "Latest computer glitch: daylight saving time". The Christian Science Monitor. Retrieved 2007-05-16.
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(help) - ^ Douglas Coate (2003). "The effects of daylight and daylight saving time on US pedestrian fatalities and motor vehicle occupant fatalities". Accident Analysis & Prevention. 36 (3): 351–357. doi:10.1016/S0001-4575(03)00015-0. PMID 15003579.
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(help)CS1 maint: multiple names: authors list (link) - ^ Jason Varughese (2001). "Fatal accidents following changes in daylight savings time: the American experience". Sleep Medicine. 2 (1): 31–36. doi:10.1016/S1389-9457(00)00032-0. PMID 11152980.
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suggested) (help) - ^ Mats Lambe (2000). "The shift to and from daylight savings time and motor vehicle crashes". Accident Analysis & Prevention. 32 (4): 609–611. doi:10.1016/S0001-4575(99)00088-3. PMID 10868764.
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suggested) (help) - ^ House Committee on Energy and Commerce, Subcommittee on Energy Conservation and Power (1985-04-24). Daylight saving time. Serial No. 99-4. U.S. GPO. p. 26.
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(help) - ^ Rachel Pain. "'When, where, if, and but': qualifying GIS and the effect of streetlighting on crime and fear". Environment and Planning A. 38 (11): 2055–2074. doi:10.1068/a38391.
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suggested) (help) - ^ a b "CSPC and USFA encourage consumers to spring forward with fire safety in mind" (Press release). U.S. Consumer Product Safety Commission; U.S. Fire Administration. 2007-03-09. Retrieved 2007-05-16.
{{cite press release}}
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(help) - ^ Helen A.S. Popkin (2007-03-02). "Changes to daylight-saving time". Consumer Reports Home & Yard Blog. Retrieved 2007-11-02.
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(help) - ^ "A timely day to check your smoke alarm" (Press release). New Zealand Fire Service. 2002-03-13. Retrieved 2007-05-15.
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(help) - ^ Amy Fackler (2005-04-08). "Prevent household fires". Yahoo Health. Retrieved 2007-05-16.
- ^ Henry Olders (2003). "Average sunrise time predicts depression prevalence". Journal of Psychosomatic Research. 55 (2): 99–105. doi:10.1016/S0022-3999(02)00479-8. PMID 12932507.
- ^ Shari Roan (2007-03-05). "Change in daylight saving time may affect moods". Los Angeles Times.
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(help) - ^ a b Alex Beam (2005-07-26). "Dim-witted proposal for daylight time". Boston Globe. Retrieved 2007-05-16.
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(help) - ^ "Daylight savings". Moderatrix Musings. 2007-03-12. Retrieved 2007-03-28.
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.)
{{cite web}}
: Check date values in:|date=
(help) - ^ Tuuli A. Lahti (2006). "Transition to daylight saving time reduces sleep duration plus sleep efficiency of the deprived sleep". Neuroscience Letters. 406 (3): 174–177. doi:10.1016/j.neulet.2006.07.024. PMID 16930838.
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suggested) (help) - ^ Thomas Kantermann (2007). "The human circadian clock's seasonal adjustment is disrupted by daylight saving time" (PDF). Current Biology. doi:10.1016/j.cub.2007.10.025. PMID 17964164. Retrieved 2007-10-27.
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ignored (help) - ^ "Kazakhstan abolishes daylight saving time". Kazakhstan Society in the UK. 2005-03-21. Retrieved 2007-03-28.
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(help) - ^ Joey Crandall (2003-10-24). "Daylight saving time ends Sunday". Record-Courier. Retrieved 2007-10-29.
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(help) - ^ Paul McDougall (2007-03-01). "PG&E says patching meters for an early daylight-saving time will cost $38 million". InformationWeek. Retrieved 2007-05-16.
{{cite news}}
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(help) - ^ "Daylight saving time: rationale and original idea". WebExhibits. Retrieved 2007-02-06.
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ignored (help) - ^ Daniel G. Schultz (2007-03-01). "Unpredictable events in medical equipment due to new daylight saving time change". Center for Devices and Radiological Health, Food and Drug Administration. Retrieved 2007-04-13.
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(help) - ^ Jesse Ruderman (2006-11-01). "Continuous daylight saving time". Indistinguishable from Jesse. Retrieved 2007-03-21.
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(help) - ^ Ann Parker (2007-03-11). "Sundials put old slant on telling time". Santa Cruz Sentinel. Retrieved 2007-05-16.
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(help) - ^ Leith Holloway (1992). "Atmospheric sun protection factor on clear days: its observed dependence on solar zenith angle and its relevance to the shadow rule for sun protection". Photochemistry and Photobiology. 56 (2): 229–34. PMID 1502267.
- ^ Winston S. Churchill (1934-04-28). "A silent toast to William Willett". Pictorial Weekly. Retrieved 2007-05-16.
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(help) - ^ Robertson Davies (1947). "XIX, Sunday". The Diary of Samuel Marchbanks. Clarke, Irwin.
- ^ Prerau. Seize the Daylight. pp. 12–24.
- ^ Prerau. Seize the Daylight. pp. 72–73.
- ^ Prerau. Seize the Daylight. pp. 51–70.
- ^ Prerau. Seize the Daylight. pp. 80–101.
- ^ a b c Joseph Myers (2007-09-16). "History of legal time in Britain". Retrieved 2007-10-24.
{{cite web}}
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(help) - ^ Prerau. Seize the Daylight. pp. 103–110.
- ^ Robert Garland (1927). Ten years of daylight saving: from the Pittsburgh standpoint. Carnegie Library of Pittsburgh. Retrieved 2007-05-16.
- ^ Prerau. Seize the Daylight. pp. 115–118.
- ^ Thomas C. Schelling (2006) [1972]. "Hockey helmets, daylight saving, and other binary choices". Micromotives and Macrobehavior. W. W. Norton. ISBN 0-393-32946-1.
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|chapterurl=
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suggested) (help) Retrieved on 2007-05-26. - ^ David P. Baron (2005). "The politics of the extension of daylight saving time". Business and its Environment (5th ed. ed.). Prentice Hall. ISBN 0-13-187355-5.
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has extra text (help) - ^ Prerau. Seize the Daylight. pp. 147–155.
- ^ Prerau. Seize the Daylight. pp. 175–180.
- ^ Joe Spagnolo (2007-03-17). "High noon for sun-slingers". The Sunday Times. Retrieved 2007-05-16.
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(help) - ^ "Single/Double Summer Time policy paper" (PDF). Royal Society for the Prevention of Accidents. Oct. 2006. Retrieved 2007-05-16.
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(help) - ^ Colin Oriti (2007-06-07). "An essential guide to Lord Howe". Lord Howe Island Tourism Association. Retrieved 2007-06-24.
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(help) - ^ "Implementation dates of daylight saving time within Australia". Bureau of Meteorology. 2007-10-30. Retrieved 2007-11-06.
{{cite web}}
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(help) - ^ Tom Baldwin (2007-03-12). "US gets summertime blues as the clocks go forward 3 weeks early". The Times. Retrieved 2007-05-16.
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(help) - ^ "Energy Policy Act of 2005, Public Law 109-58 § 110". 2005-08-08. Retrieved 2007-05-10.
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(help) - ^ "Historia de la hora oficial de Chile" (in Spanish). Chilean Hydrographic and Oceanographic Service. 2007-05-17. Retrieved 2007-11-06.
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(help) - ^ "Time zones & daylight saving time". Institute for National Measurement Standards. 2007-05-05. Retrieved 2007-05-10.
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(help) - ^ Philip Johnston (2007-01-22). "Is it time to lighten our darkness?". The Daily Telegraph. Retrieved 2007-05-16.
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(help) - ^ Doug O'Hara (2007-03-11). "Alaska: daylight stealing time". Far North Science. Retrieved 2007-05-11.
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(help) - ^ "Decretos sobre o Horário de Verão no Brasil" (in Portuguese). Time Service Dept., National Observatory, Brazil. 2007. Retrieved 2007-11-06.
- ^ Richard A. Meade (1978). "Language change in this century". English Journal. 67 (9): 27–30. doi:10.2307/815124. | Joseph P. Pickett; et al. (eds.). "daylight-saving time". The American Heritage Dictionary of the English Language (4th ed. (2000) ed.). Boston: Houghton Mifflin. ISBN 0-395-82517-2.
variant forms: or daylight-savings time
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suggested) (help) Retrieved on 2007-05-26. | "daylight saving time". Merriam-Webster's Online Dictionary. Retrieved 2007-03-08.called also daylight saving, daylight savings, daylight savings time, daylight time
| "15 U.S.C. § 260a notes". Retrieved 2007-05-09.Congressional Findings; Expansion of Daylight Saving Time
- ^ "Time talk". Language Realm. 2007. Retrieved 2007-10-24.
- ^ Paul Eggert (2007-10-01). "Sources for time zone and daylight saving time data". Retrieved 2007-10-24.
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(help); Unknown parameter|coauthors=
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suggested) (help) - ^ "tztab(4)". HP-UX Reference: HP-UX 11i Version 3. Hewlett-Packard Co. 2007. Retrieved 2007-05-16.
- ^ "Other environment variables". IEEE Std 1003.1-2004. The Open Group. 2004. Retrieved 2007-05-16.
- ^ "Daylight saving time help and support center". Microsoft Corp. 2007-09-14. Retrieved 2007-10-24.
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(help) - ^ "Visual Studio and daylight saving time change". Microsoft Corp. 2007. Retrieved 2007-03-22.
- ^ "Windows daylight savings timezones for Israel". Lingnu Open Source Consulting. 2005-04-20. Retrieved 2007-03-22.
{{cite web}}
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(help) - ^ "Microsoft support entry regarding daylight saving time in Israel" (in Hebrew). Microsoft Corp. 2007. Retrieved 2007-03-22.
References
- Ian R. Bartky (1979). "Standard and daylight-saving time". Scientific American. 240 (5): 46–53. ISSN 0036-8733.
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: Unknown parameter|coauthors=
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suggested) (help) - Michael Downing (2005). Spring Forward: The Annual Madness of Daylight Saving Time. Shoemaker & Hoard. ISBN 1-59376-053-1. Retrieved 2007-05-16.
- David Prerau (2005). Seize the Daylight: The Curious and Contentious Story of Daylight Saving Time. Thunder’s Mouth Press. ISBN 1-56025-655-9. Retrieved 2007-05-16. The British version, focusing on the UK, is Saving the Daylight: Why We Put the Clocks Forward. Granta Books. ISBN 1-86207-796-7. Retrieved 2007-05-16.
External links
- Daylight Saving Time - general history and anecdotes
- Saving Time, Saving Energy - North American viewpoint
- Summer Time - European viewpoint
- Sources for time zone and daylight saving time data - technical resources