Daylight saving time (DST)—also summer time in several countries[1][2][3][4][5][6][7] in British English, and European official terminology (see Terminology)—is the practice of advancing clocks so that evenings 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.[8]
The modern idea of daylight saving was first proposed in 1895 by George Vernon Hudson [9] and it was first implemented during the First World War. Many countries have used it at various times since then. Although most of the United States used DST throughout the 1950s and 1960s, DST use expanded following the 1970s energy crisis and has generally remained in use in North America and Europe since that time.
The practice has been both praised and criticized.[8] Adding daylight to evenings benefits retailing, sports, and other activities that exploit sunlight after working hours,[10] but can cause problems for evening entertainment and other occupations tied to the sun.[11][12] Although an early goal of DST was to reduce evening usage of incandescent lighting (formerly a primary use of electricity[13]), modern heating and cooling usage patterns differ greatly, and research about how DST currently affects energy use is limited or contradictory.[14]
DST clock shifts present other challenges. They complicate timekeeping, and can disrupt meetings, travel, billing, recordkeeping, medical devices, heavy equipment,[15] and sleep patterns.[16] Software can often adjust computer clocks automatically, but this can be limited and error-prone, particularly when DST protocols are changed.[17]
Justification and rationale
As modern societies operate on the basis of “standard time” rather than solar time, most people’s schedules are not governed by the movements of the earth in relation to the sun. For example, work, school and transport schedules will generally begin at exactly the same time at all times of the year regardless of the position of the sun. However, in non-equatorial regions the total number of hours of sunlight in a day will vary a great deal between winter and summer. As a result, if “standard time” is applied year round, a significant portion of the longer sunlight hours will fall in the early morning while there may still be a significant period of darkness in the evening. Because many people will tend to sleep in the early morning hours, these hours of sunlight are wasted for them, whereas if they are shifted to the evening via DST, they can then be used. As days shorten again in autumn/winter, sunrises get later and later, meaning that people could then be waking up and spending a significant portion of their mornings in the dark, so clocks are then returned to the “standard” time. In theory, people who need to or want to could simply wake up earlier to take advantage of the sunlight then, but this is impractical because of the inflexibility of clock-based schedules.
The actual effects of DST can vary significantly by location depending on its latitude and position relative to the centre of its time zone. For example, DST does not have much practical effect in extremely northern or southern locations because the very long/short days mean that the artificial manipulation of time has little or no real impact on daily life since sunrise/sunset times are already dramatically out of synch with modern working hours.[18] DST is also of no use for locations near the equator because they see only a very small variation in daylight through the year.[19]
History
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 hours regardless of day length, so that each daylight hour was longer during summer.[20] 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.[21] 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[22] and all Jewish ceremonies.[23]
During his time as an American envoy to France, Benjamin Franklin, publisher of the old English proverb, “Early to bed, and early to rise, makes a man healthy, wealthy and wise”,[24][25] anonymously published a letter suggesting that Parisians economize on candles by rising earlier to use morning sunlight.[26] This 1784 satire proposed taxing shutters, rationing candles, and waking the public by ringing church bells and firing cannons at sunrise.[27] Franklin did not propose DST; like ancient Rome, 18th-century Europe did not keep precise schedules. However, this soon changed as rail and communication networks came to require a standardization of time unknown in Franklin’s day.[28]
Modern DST was first proposed by the New Zealand entomologist George Vernon Hudson, whose shift-work job gave him leisure time to collect insects, and led him to value after-hours daylight.[9] In 1895 he presented a paper to the Wellington Philosophical Society proposing a two-hour daylight-saving shift,[29] and after considerable interest was expressed in Christchurch, New Zealand, he followed up in an 1898 paper.[30] Many publications incorrectly credit DST’s proposal to the prominent English builder and outdoorsman William Willett,[31] who independently conceived DST in 1905 during a pre-breakfast ride, when he observed with dismay how many Londoners slept through a large part of a summer’s day.[32] An avid golfer, he also disliked cutting short his round at dusk.[33] His solution was to advance the clock during the summer months, a proposal he published two years later.[34] The proposal was taken up by the Liberal Member of Parliament (MP) Robert Pearce, who introduced the first Daylight Saving Bill to the House of Commons on 12 February 1908.[35] A select committee was set up to examine the issue, but Pearce’s bill did not become law, and several other bills failed in the following years. Willett lobbied for the proposal in the UK until his death in 1915.
Starting on 30 April 1916, Germany and its World War I allies were the first to use DST (German: Sommerzeit) as a way to conserve coal during wartime. 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.
Broadly speaking, Daylight Saving Time was abandoned in the years after the war (with some notable exceptions including Canada, the UK, France, and Ireland for example). However, it was brought back for periods of time in many different places in the coming decades, widely during the Second World War. It became widely adopted, particularly in North America and Europe starting in the 1970s as a result of the 1970s energy crisis.
Since then, the world has seen many enactments, adjustments, and repeals.[36] For specific details, an overview is available at Daylight saving time by country.
Procedure
In the case of the United States where a one-hour shift occurs at 02:00 local time, in spring the clock jumps forward from the last moment of 01:59 standard time to 03:00 DST and that day has 23 hours, whereas in autumn the clock jumps backward from the last moment of 01:59 DST to 01:00 standard time, repeating that hour, and that day has 25 hours. A digital display of local time does not read 02:00 exactly at the shift to summertime, but instead jumps from 01:59:59.9 forward to 03:00:00.0. In the European Union, on the other hand, since the shift occurs at 01:00 UTC, the autumn shift happens an hour later than the spring shift, local time.
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.[37] 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 or 02:00 CET or 3:00 EET; for example, Eastern European Time is always one hour ahead of Central European Time.[38] 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. In the past, Australian districts went even further and did not always agree on start and end dates; for example, in 2008 most DST-observing areas shifted clocks forward on October 5 but Western Australia shifted on October 26.[39] In some cases only part of a country shifts; for example, in the US, Hawaii and most of Arizona do not observe DST.[40]
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.[38] 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.[41] The 2007 US 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 now that an energy-consumption study has been done.[42]
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.[43] The time difference between the United Kingdom and mainland Chile may therefore be five hours during the Northern summer, three hours during the Northern winter and four hours a few weeks per year because of mismatch of changing dates.
Xinjiang Uyghur Autonomous Region in western China, Iceland, Russia 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.[44] Conversely, northeast India and a few other areas skew time zones eastward, in effect observing negative DST.[45] 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.[46]
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 at165°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.[47] Double daylight saving time has been used on occasion; for example, it was used in some European countries during World War II[38] when it was referred to as “Double Summer Time”. See British Double Summer Time and Central European Midsummer Time for details.
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.[48] Only a minority of the world’s population uses DST because Asia and Africa generally do not observe it.
Politics
Daylight saving has caused controversy since it began.[8] 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”[49] and pundits have dubbed it “Daylight Slaving Time”.[50] Historically, retailing, sports and tourism interests have favoured daylight saving, while agricultural and evening entertainment interests have opposed it, and its initial adoption had been prompted by energy crisis and war.[51]
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.[52] The US was even more skeptical: Andrew Peters introduced a DST bill to the US House of Representatives in May 1909, but it soon died in committee.[53]
After Germany led the way with starting DST (German: Sommerzeit) during World War I on 30 April 1916 together with its allies to alleviate hardships from wartime coal shortages and air raid blackouts, the political equation changed in other countries; the United Kingdom used DST first on 21 May 1916.[54] US retailing and manufacturing interests led by Pittsburgh industrialist Robert Garland soon began lobbying for DST, but were opposed by railroads. The US’s 1917 entry to the war overcame objections, and DST was established in 1918.[55]
The 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.[38] The US 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.[56] Only a few US cities retained DST locally thereafter,[57] including New York so that its financial exchanges could maintain an hour of arbitrage trading with London, and Chicago and Cleveland to keep pace with New York.[58] 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. Some businesses followed suit though many others did not; the experiment was not repeated.[59]
Since Germany’s adoption in 1916 the world has seen many enactments, adjustments, and repeals of DST, with similar politics involved.[60] The history of time in the United States includes DST during both world wars, but no standardization of peacetime DST until 1966.[61][62] In May 1965, for two weeks, St. Paul and Minneapolis were on different times, when the capital city decided to join most of the nation by starting Daylight Saving Time while Minneapolis opted to follow the later date set by state law. [63] 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 US DST, and both Idaho senators voted for it based on the premise that during DST fast-food restaurants sell more French fries, which are made from Idaho potatoes.[10]In 1992 after a three-year trial of daylight saving in Queensland, Australia, a referendum on daylight saving was held and defeated with a 54.5% ‘no’ vote – with regional and rural areas strongly opposed, while those in the metropolitan south-east were in favour.[64] In 2005, the Sporting Goods Manufacturers Association and the National Association of Convenience Stores successfully lobbied for the 2007 extension to US DST.[65]In December 2008, the Daylight Saving for South East Queensland(DS4SEQ) political party was officially registered in Queensland, advocating the implementation of a dual-time zone arrangement for Daylight Saving in South East Queensland while the rest of the state maintains standard time.[66] DS4SEQ contested the March 2009 Queensland State election with 32 candidates and received one percent of the state-wide primary vote, equating to around 2.5% across the 32 electorates contested.[67] After a three-year trial, more than 55% of Western Australians voted against DST in 2009, with rural areas strongly opposed.[68] On 14 April 2010, after being approached by the DS4SEQ political party, Queensland Independent member Peter Wellington, introduced the Daylight Saving for South East Queensland Referendum Bill 2010 intoQueensland Parliament, calling for a referendum to be held at the next State election on the introduction of daylight saving into South East Queensland under a dual-time zone arrangement.[69] The Bill was defeated in Queensland Parliament on 15 June 2011.[70]
In the UK the Royal Society for the Prevention of Accidents supports a proposal to observe SDST’s additional hour year-round, but is opposed in some industries, such as postal workers and farmers, and particularly by those living in the northern regions of the UK.[71]
In some Muslim countries DST is temporarily abandoned during Ramadan (the month when no food should be eaten until sunset), since the DST would delay the evening dinner. Ramadan takes place in July and August in 2012. This concerns at least Morocco and Palestine,[72] although Iran keeps DST during Ramadan.[73] Most Muslim countries do not use DST, partially for this reason.
The 2011 declaration by Russia that it would not turn its clocks back and stay in DST all year long was subsequently followed by a similar declaration from Belarus.[74]
