Daylight saving time

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This article is about DST in general. For your location's rules, see Daylight saving time around the world.
File:DaylightSaving-World-Subdivisions.png
Although not used by most of the world's people, daylight saving time is common in high latitudes.
  DST used
  DST no longer used
  DST never used

Daylight saving time (DST; also summer time in British English; see Terminology) 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 is controversial.[1] Adding daylight to afternoons benefits retailing, sports, and other activities that exploit sunlight after working hours,[2] but causes problems for farming, entertainment and other occupations tied to the sun.[3][4] Extra afternoon daylight reduces traffic fatalities;[5] its effect on health and crime is less clear. Although an early goal of DST was to reduce evening usage of incandescent lighting, formerly a primary use of electricity,[6] modern heating and cooling usage patterns can cause DST to increase electricity consumption.[7]

DST's clock shifts can serve as fire safety reminders,[8] but they complicate timekeeping and can disrupt meetings, travel, billing, recordkeeping, medical devices, and heavy equipment.[9] Many computer-based systems can adjust their clocks automatically, but this can be limited and error-prone, particularly when DST rules change.[10]

Origin

File:Clepsydra-Diagram-Fancy.jpeg
In this ancient water clock, a series of gears rotated a cylinder to display hour lengths appropriate for each day's date.

Although not punctual in the modern sense, ancient civilizations adjusted daily schedules to the sun more flexibly than modern DST does, often dividing daylight into twelve equal hours regardless of day length, so that each daylight hour was longer during summer.[11] 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.[12] 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.[13]

File:Franklin-Benjamin-LOC.jpg
Benjamin Franklin suggested firing cannons at sunrise to waken Parisians.

During his time as an American envoy to France, Benjamin Franklin, author of the proverb, "Early to bed, and early to rise, makes a man healthy, wealthy and wise", anonymously published a letter suggesting that Parisians economize on candles by rising earlier to use morning sunlight.[14] This 1784 satire proposed taxing shutters, rationing candles, and waking the public by ringing church bells and firing cannons at sunrise.[15] 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.[16]

File:William-Willett.jpg
William Willett invented DST and advocated it tirelessly.[17]

The prominent English builder and outdoorsman William Willett invented DST in 1905 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.[18] 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.[19] He lobbied unsuccessfully for the proposal until his death in 1915; see Politics for more details.

Germany, its World War I allies, and their occupied zones were the first European nations to use Willett's invention, starting April 30, 1916. Britain, most of its allies, and many European neutrals soon followed suit; Russia and a few other countries waited until the next year; and the United States adopted it in 1918. Since then, the world has seen many enactments, adjustments, and repeals.[20]

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.[19] 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.[21]

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.[22] 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.[23]

Energy use

Delaying the nominal time of sunset and sunrise reduces the use of artificial light in the evening and increases it in the morning. As Franklin's 1784 satire pointed out, lighting costs are reduced if the evening reduction outweighs the morning increase, as in high-latitude summer when most people wake up well after sunrise. An early goal of DST was to reduce evening usage of incandescent lighting, formerly a primary use of electricity.[6] Although energy conservation remains an important goal,[24] studies are contradictory, and suggest that DST can increase energy use in some common cases:

  • 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,[25] but the National Bureau of Standards (NBS) reviewed the DOT study in 1976 and found no significant energy savings.[21]
  • 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.[26]
  • In Western Australia during summer 2006–07, DST increased electricity consumption during hotter days and decreased it during cooler days, with consumption rising 0.6% overall.[27]
  • Although a 2007 study estimated that introducing DST to Japan would reduce household lighting energy consumption,[28] 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.[29]
  • DST may increase gasoline consumption: U.S. gasoline demand grew an extra 1% during the newly introduced DST in March 2007.[30]
  • A 2007 study found that the earlier start to DST that year had little or no effect on electricity consumption in California.[31]
  • A 2007 study estimated that winter daylight saving would prevent a 2% increase in average daily electricity consumption in Great Britain.[32]
  • A 2008 study examined billing data in Indiana before and after it adopted DST in 2006, and concluded that DST increased residential electricity consumption by 1% to 4%, primarily due to extra afternoon cooling.[7]

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.[33] 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.[34] Conversely, DST can adversely affect farmers and others whose hours are set by the sun.[3] 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.[35] DST also hurts prime-time broadcast ratings[4] and drive-in and other theaters.[36]

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.[37] 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.[38]

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%,[25] but the 1976 NBS review of the DOT study found no differences in traffic fatalities.[21] In 1995 the Insurance Institute for Highway Safety estimated a reduction of 1.2%, including a 5% reduction in crashes fatal to pedestrians.[5] Others have found similar reductions.[39] 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.[40] It is not clear whether sleep disruption contributes to fatal accidents immediately after the spring clock shifts.[41] A correlation between clock shifts and accidents has been observed in North America but not in Finland or Sweden. If this effect exists, it is far smaller than the overall reduction in fatalities.[42]

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".[43] Outdoor lighting has a marginal and sometimes even contradictory influence on crime and fear of crime.[44]

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, particularly 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.[45][46][8] This is not an essential function of DST, as locations without DST can instead use the first days of spring and autumn as reminders.[47]

Health

File:Greenwich GB DaylightChart.png
Clock shifts affect apparent sunrise and sunset times at Greenwich in 2007.[48]

DST has mixed effects on health. In societies with fixed work schedules it provides more afternoon sunlight for outdoor exercise.[49] 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.[50] Sunlight strongly influences seasonal affective disorder. DST may help in depression by causing individuals to rise earlier,[51] but some argue the reverse.[52] The Retinitis Pigmentosa Foundation Fighting Blindness, chaired by blind sports magnate Gordon Gund, successfully lobbied in 1985 and 2005 for U.S. DST extensions,[2][53] but DST can hurt night blindness sufferers.[54]

Clock shifts disrupt sleep and reduce its efficiency.[55] Effects on seasonal adaptation of the circadian rhythm can be severe and last for weeks.[56] A 2008 study found that although male suicide rates rise in the weeks after the spring transition, the relationship weakened greatly after adjusting for season.[57] The government of Kazakhstan cited health complications due to clock shifts as a reason for abolishing DST in 2005.[58]

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.[59] As more devices contain clocks, more time is spent changing them.[60] 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.[61] During an autumn transition from 02:00 to 01:00, a clock reads times from 01:00 to 02:00 twice, possibly leading to confusion.[62]

Some computer-based systems require downtime or restarting when clocks shift; ignoring this requirement damaged a German steel facility in 1993.[9] Medical devices may generate adverse events that could harm patients, without being obvious to clinicians responsible for care.[63] 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.[10]

Some clock-shift problems could be avoided by adjusting clocks continuously[64] or at least more gradually—for example, Willett originally suggested weekly 20-minute transitions—but this would add complexity and has never been implemented.

File:Willett memorial.JPG
The William Willett Memorial Sundial is always on DST.

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.[65] Also, sun-exposure rules like "avoid the sun within two hours of noon" become less accurate when DST is in effect.[66]

Politics

Daylight saving has caused controversy since it began.[1] 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".[67] 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",[68] and wags have dubbed it "Daylight Slaving Time".[69] Historically, retailing, sports and tourism interests have favored daylight saving, while agricultural and evening entertainment interests have opposed it, and its initial adoption has been prompted by energy crisis and war.[70]

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.[71] 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.[72]

File:Victory-Cigar-Congress-Passes-DST.jpeg
Retailers generally favor DST. United Cigar Stores hailed a 1918 DST bill.

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.[73] 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.[74]

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.[75] 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,[76] and only a few U.S. cities retained DST locally thereafter.[77] 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.[78]

Since Willett's day the world has seen many enactments, adjustments, and repeals of DST, with similar politics involved.[79] The history of time in the United States includes DST during both world wars, but no standardization of peacetime DST until 1966.[80] 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;[2] in 2005, the Sporting Goods Manufacturers Association and the National Association of Convenience Stores successfully lobbied for the 2007 extension to U.S. DST.[53] In early 2007, Western Australia continued to debate a trial use of DST and several politicians changed positions after public sentiment swung against it.[81] In the UK the sport and leisure industry supports a proposal to observe SDST's additional hour year-round.[82]

Observance practices

Main article: Daylight saving time around the world
File:DST begin.svg
Clocks advance when DST starts.

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.[83] 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.[75] 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.[84]

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.[75] Starting in 2007, most of the United States and Canada observe DST from the second Sunday in March to the first Sunday in November, almost two-thirds of the year.[85] 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.[86]

File:Time-differences-brz-us.png
In 2008 central Brazil will be one, two, or three hours ahead of eastern U.S., depending on the date.[87]

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.[88] The time difference between the United Kingdom and mainland Chile may therefore be three, four, or five hours, depending on the time of year.

File:2007-02-20 time zones.svg
Time zones often lie west of their idealized boundaries, resulting in year-round DST.

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 the time in Saskatchewan is Central Standard Time (90° W) year-round, so Saskatoon is always about 67 minutes ahead of mean solar time.[89] Conversely, northeast India and a few other areas skew time zones eastward, in effect observing negative DST.[24] 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.[90]

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.[91]

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.[92] 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, as in daylight-saving time. Daylight savings time, daylight savings, and daylight time are common variants, the savings by analogy to savings account.[93] Willett's original proposal used the term daylight saving, but by 1911 the term summer time replaced daylight saving time in draft legislation in Britain.[94]

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).

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 …"[95] works only in the northern hemisphere, and is less robust against future rule changes.

Computing

File:Daylightsavings.jpg
A 2001 public service announcement reminded people to adjust clocks manually.

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. Some applications standardize on UTC to avoid problems with clock shifts and time zone differences.[96]

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;[97] HP's "tztab" database is similar but incompatible.[98] When temporal authorities change DST rules, zoneinfo updates are installed as part of ordinary system maintenance. In Unix-like systems the 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.[99]

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.[100] 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.[101]

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[102] and a Microsoft tool that switches zones automatically.[103]

References

File:Franklin-Benjamin-Journal-de-Paris-1784.jpg
Franklin's 1784 letter about daylight had neither title nor byline.[15]
File:Waste-of-Daylight-19-cover.jpg
William Willett's pamphlet promoting DST went through nineteen editions.[19]
  1. ↑ 1.0 1.1 See Further reading for full citations to these books:
    • Downing. Spring Forward.
    • Prerau. Seize the Daylight.
  2. ↑ 2.0 2.1 2.2 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 2007-12-14.
  3. ↑ 3.0 3.1 Effect on those whose hours are set by the sun:
    • Downing. Spring Forward. pp. 19–33.
    • Prerau. Seize the Daylight. pp. 103–110, 149–151, 198.
  4. ↑ 4.0 4.1 Rick Kissell (2007-03-20). "Daylight-saving dock ratings". Variety. Retrieved 2007-05-16.
  5. ↑ 5.0 5.1 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): 92–95. PMID 7832269. Retrieved 2007-07-14. Unknown parameter |coauthors= ignored (help)
  6. ↑ 6.0 6.1 Roscoe G. Bartlett (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 2007-12-14.
  7. ↑ 7.0 7.1 Matthew J. Kotchen; Laura E. Grant (2008-02-08). "Does daylight saving time save energy? evidence from a natural experiment in Indiana" (PDF). Preliminary Program. Environmental and Energy Economics Program Meeting. National Bureau of Economic Research. Retrieved 2008-03-03.
  8. ↑ 8.0 8.1 "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.
  9. ↑ 9.0 9.1 Peter G. Neumann (1994). "Computer date and time problems". Computer-Related Risks. Addison-Wesley. ISBN 0-201-55805-X. Retrieved on 2007-05-26.
  10. ↑ 10.0 10.1 Stephen Tong (2007). "Are you prepared for daylight saving time in 2007?". IT Professional. IEEE Computer Society. 9 (1): 36–41. Retrieved 2007-05-16. Unknown parameter |coauthors= ignored (help)
  11. ↑ B.L. Ullman (1918). "Daylight saving in ancient Rome". The Classical Journal. 13 (6): 450–451.
  12. ↑ 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.
  13. ↑ Robert Kaplan (2003). "The holy mountain". Atlantic. 292 (5): 138–141.
  14. ↑ Seymour Stanton Block (2006). "Benjamin Franklin: America's inventor". American History. Retrieved 2007-02-16.
  15. ↑ 15.0 15.1 Benjamin Franklin, writing anonymously (1784-04-26). "Aux auteurs du Journal". Journal de Paris (in French) (117). 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.
  16. ↑ Eviatar Zerubavel (1982). "The standardization of time: a sociohistorical perspective". The American Journal of Sociology. 88 (1): 1–23.
  17. ↑ Prerau. Seize the Daylight. p. 22.
  18. ↑ David Rooney (2007). "Royal Observatory commemorates William Willett". Petts Wood & District Residents' Association. Retrieved 2007-03-27.
  19. ↑ 19.0 19.1 19.2 Willett pamphlet:
  20. ↑ Prerau. Seize the Daylight. pp. 51–89.
  21. ↑ 21.0 21.1 21.2 Template:Cite paper
  22. ↑ Thomas C. Schelling (2006) [1972]. "Hockey helmets, daylight saving, and other binary choices" (PDF). Micromotives and Macrobehavior. W. W. Norton. ISBN 0-393-32946-1. Retrieved on 2007-05-26.
  23. ↑ Template:Cite paper
  24. ↑ 24.0 24.1 Dilip R. Ahuja; D. P. Sen Gupta; V. K. Agrawal (2007). "Energy savings from advancing the Indian Standard Time by half an hour" (PDF). Current Science. 93 (3): 298–302.
  25. ↑ 25.0 25.1 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 2007-12-14.
  26. ↑ Template:Cite paper
  27. ↑ "The facts on electricity consumption and daylight saving" (Press release). Western Power. 2007-10-31. Retrieved 2008-03-17.
  28. ↑ Wee-Kean Fong; Hiroshi Matsumoto; Yu-Fat Lun; Ryushi Kimura (2007). "Energy savings potential of the Summer Time concept in different regions of Japan from the perspective of household lighting". Journal of Asian Architecture and Building Engineering. 6 (2): 371–378. doi:10.3130/jaabe.6.371.
  29. ↑ 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. Unknown parameter |coauthors= ignored (help)
  30. ↑ Shawn McCarthy (2007-04-18). "Has daylight saving time fuelled gasoline consumption?". Globe and Mail.
  31. ↑ Template:Cite paper
  32. ↑ Template:Cite paper
  33. ↑ Dana Knight (2006-04-17). "Daylight-saving time becomes daylight-spending time for many businesses". Indianapolis Star.
  34. ↑ Downing. Spring Forward. pp. 147–148.
  35. ↑ "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." ' 
  36. ↑ Todd D. Rakoff (2002). A Time for Every Purpose: Law and the Balance of Life. Harvard University Press. p. 26. ISBN 067400910X.
  37. ↑ Mark J. Kamstra (2000). "Losing sleep at the market: the daylight saving anomaly". The American Economic Review. 90 (4): 1005–1011. Unknown parameter |coauthors= ignored (help)
  38. ↑ Ben Arnoldy (2007-03-07). "Latest computer glitch: daylight saving time". Christian Science Monitor. Retrieved 2007-05-16.
  39. ↑ 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. Unknown parameter |coauthors= ignored (help)
  40. ↑ Template:Cite paper
  41. ↑ Alex Vincent (1998). "Effects of daylight savings time on collision rates". N Engl J Med. 339 (16): 1167–8. PMID 9776656. Unknown parameter |coauthors= ignored (help) Data supporting Coren's half of this exchange are in: Stanley Coren (1998). "Sleep deficit, fatal accidents, and the spring shift to daylight savings time". INABIS '98.
  42. ↑ Clock shifts and accidents:
  43. ↑ 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.
  44. ↑ 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. Unknown parameter |coauthors= ignored (help)
  45. ↑ Helen A.S. Popkin (2007-03-02). "Changes to daylight-saving time". Consumer Reports Home & Yard Blog. Retrieved 2007-11-02.
  46. ↑ "A timely day to check your smoke alarm" (Press release). New Zealand Fire Service. 2002-03-13. Retrieved 2007-05-15.
  47. ↑ Amy Fackler (2005-04-08). "Prevent household fires". Yahoo Health. Retrieved 2007-05-16.
  48. ↑ Sualeh Fatehi (2008). "Daylight Chart". SourceForge.net. Retrieved 2008-03-08.
  49. ↑ Prerau. Seize the Daylight. pp. 20, 65, 85.
  50. ↑ A.V. Parisi; J. Turner; D.J. Turnbull; P. Schouten; N. Downs (2008). "Influence of summer daylight saving time on scattered erythemal solar ultraviolet exposures". Journal of Photochemistry and Photobiology B: Biology. 91 (1): 35–40. doi:10.1016/j.jphotobiol.2008.01.010. PMID 18321724.
  51. ↑ 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.
  52. ↑ Shari Roan (2007-03-05). "Change in daylight saving time may affect moods". Los Angeles Times.
  53. ↑ 53.0 53.1 Alex Beam (2005-07-26). "Dim-witted proposal for daylight time". Boston Globe. Retrieved 2007-05-16.
  54. ↑ "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.)
  55. ↑ Tuuli A. Lahti; Sami Leppämäki; Jouko Lönnqvist; Timo Partonen (2008). "Transitions into and out of daylight saving time compromise sleep and the rest-activity cycles". BMC Physiol. 8: 3. doi:10.1186/1472-6793-8-3. PMID 18269740.
  56. ↑ Thomas Kantermann (2007). "The human circadian clock's seasonal adjustment is disrupted by daylight saving time" (PDF). Current Biology. 17 (22): 1996–2000. doi:10.1016/j.cub.2007.10.025. PMID 17964164. Retrieved 2007-10-27. Lay summary – ABC Science Online, Australia (2007-10-25). Unknown parameter |coauthors= ignored (help)
  57. ↑ Michael Berk; Seetal Dodd; Karen Hallam; Lesley Berk; John Gleeson; Margaret Henry (2008). "Small shifts in diurnal rhythms are associated with an increase in suicide: the effect of daylight saving". Sleep and Biological Rhythms. 6 (1): 22–25. doi:10.1111/j.1479-8425.2007.00331.x.
  58. ↑ "Kazakhstan abolishes daylight saving time". Kazakhstan Society in the UK. 2005-03-21. Retrieved 2007-03-28.
  59. ↑ Joey Crandall (2003-10-24). "Daylight saving time ends Sunday". Record-Courier. Retrieved 2007-10-29.
  60. ↑ Steve Moyer (2007-03-06). "Daylight-saving time change could affect computers, electronics". Nevada Daily Mail. Retrieved 2008-03-02.
  61. ↑ 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.
  62. ↑ "Daylight saving time: rationale and original idea". WebExhibits. Retrieved 2008-03-09. Unknown parameter |note= ignored (help)
  63. ↑ 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 2007-11-11.
  64. ↑ Jesse Ruderman (2006-11-01). "Continuous daylight saving time". Indistinguishable from Jesse. Retrieved 2007-03-21.
  65. ↑ Ann Parker (2007-03-11). "Sundials put old slant on telling time". Santa Cruz Sentinel. Retrieved 2008-03-08.
  66. ↑ 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. doi:10.1111/j.1751-1097.1992.tb02151.x. PMID 1502267.
  67. ↑ Winston S. Churchill (1934-04-28). "A silent toast to William Willett". Pictorial Weekly. Retrieved 2007-05-16. Check date values in: |date= (help)
  68. ↑ Robertson Davies (1947). "XIX, Sunday". The Diary of Samuel Marchbanks. Clarke, Irwin. OCLC 1246640.
  69. ↑ Prerau. Seize the Daylight. p. 117.
  70. ↑ Prerau. Seize the Daylight. pp. xi.
  71. ↑ Prerau. Seize the Daylight. pp. 12–24.
  72. ↑ Prerau. Seize the Daylight. pp. 72–73.
  73. ↑ Prerau. Seize the Daylight. pp. 51–70.
  74. ↑ Prerau. Seize the Daylight. pp. 80–101.
  75. ↑ 75.0 75.1 75.2 Joseph Myers (2007-09-16). "History of legal time in Britain". Retrieved 2007-10-24.
  76. ↑ Prerau. Seize the Daylight. pp. 103–110.
  77. ↑ Robert Garland (1927). Ten years of daylight saving from the Pittsburgh standpoint. Carnegie Library of Pittsburgh. OCLC 30022847. Retrieved 2008-03-08.
  78. ↑ Prerau. Seize the Daylight. pp. 115–118.
  79. ↑ 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.
  80. ↑ Prerau. Seize the Daylight. pp. 147–155, 175–180.
  81. ↑ Joe Spagnolo (2007-03-17). "High noon for sun-slingers". Sunday Times. Retrieved 2007-05-16.
  82. ↑ "Single/Double Summer Time policy paper" (PDF). Royal Society for the Prevention of Accidents. Oct. 2006. Retrieved 2007-05-16. Check date values in: |date= (help)
  83. ↑ Colin Oriti (2007). "Getting to Lord Howe Island". Lord Howe Island Tourism Association. Retrieved 2008-03-08.
  84. ↑ "Implementation dates of daylight saving time within Australia". Bureau of Meteorology. 2007-10-30. Retrieved 2007-11-06.
  85. ↑ Tom Baldwin (2007-03-12). "US gets summertime blues as the clocks go forward 3 weeks early". The Times. Retrieved 2007-05-16.
  86. ↑ "Energy Policy Act of 2005, Public Law 109-58 § 110". 2005-08-08. Retrieved 2007-05-10.
  87. ↑ "Graphical display of time zones and daylight saving times". 2008. Retrieved 2008-01-26.
  88. ↑ "Historia de la hora oficial de Chile" (in Spanish). Chilean Hydrographic and Oceanographic Service. 2007-05-17. Retrieved 2007-11-06.
  89. ↑ "Time zones & daylight saving time". Institute for National Measurement Standards. 2007-05-05. Retrieved 2007-05-10.
  90. ↑ Philip Johnston (2007-01-22). "Is it time to lighten our darkness?". Daily Telegraph. Retrieved 2007-05-16.
  91. ↑ Doug O'Harra (2007-04-01). "Alaska: daylight stealing time". Far North Science. Retrieved 2007-12-14.
  92. ↑ "Decretos sobre o Horário de Verão no Brasil" (in Portuguese). Time Service Dept., National Observatory, Brazil. 2007. Retrieved 2007-11-06.
  93. ↑ Daylight saving time and its variants:
    • 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 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
  94. ↑ Prerau. Seize the Daylight. p. 22.
  95. ↑ "Time talk". Language Realm. 2007. Retrieved 2007-10-24.
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  97. ↑ Paul Eggert (2007-12-26). "Sources for time zone and daylight saving time data". Retrieved 2007-12-31. Unknown parameter |coauthors= ignored (help)
  98. ↑ "tztab(4)". HP-UX Reference: HP-UX 11i Version 3. Hewlett-Packard Co. 2007. Retrieved 2007-05-16.
  99. ↑ "Other environment variables". IEEE Std 1003.1-2004. The Open Group. 2004. Retrieved 2007-05-16.
  100. ↑ "Daylight saving time help and support center". Microsoft Corp. 2007-09-14. Retrieved 2007-10-24.
  101. ↑ "Visual Studio and daylight saving time change". Microsoft Corp. 2007. Retrieved 2007-03-22.
  102. ↑ "Windows daylight savings timezones for Israel". Lingnu Open Source Consulting. 2005-04-20. Retrieved 2007-03-22.
  103. ↑ "Microsoft support entry regarding daylight saving time in Israel" (in Hebrew). Microsoft Corp. 2007. Retrieved 2007-03-22.

Further reading

  • Michael Downing (2005). Spring Forward: The Annual Madness of Daylight Saving Time. Shoemaker & Hoard. ISBN 1-59376-053-1.
  • David Prerau (2005). Seize the Daylight: The Curious and Contentious Story of Daylight Saving Time. Thunder’s Mouth Press. ISBN 1-56025-655-9. The British version, focusing on the UK, is Saving the Daylight: Why We Put the Clocks Forward. Granta Books. ISBN 1-86207-796-7.

External links

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