Daylight saving time
Overview
 
Daylight saving time (DST)—also summer time in several countries including in British English
British English
British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...

 and European official terminology (see Terminology)—is the practice of temporarily advancing clocks
Time zone
A time zone is a region on Earth that has a uniform standard time for legal, commercial, and social purposes. In order for the same clock time to always correspond to the same portion of the day as the Earth rotates , different places on the Earth need to have different clock times...

 during the summertime so that afternoons have more daylight
Daylight
Daylight or the light of day is the combination of all direct and indirect sunlight outdoors during the daytime. This includes direct sunlight, diffuse sky radiation, and both of these reflected from the Earth and terrestrial objects. Sunlight scattered or reflected from objects in outer space is...

 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 1895 by George Vernon Hudson
George Vernon Hudson
George Vernon Hudson was an English-born New Zealand entomologist and astronomer.Born in London, Hudson was the sixth child of Charles Hudson, an artist and stained-glass window designer. By the age of 14 he had built up a collection of British insects, and had published a paper in The Entomologist...

.
Encyclopedia
Daylight saving time (DST)—also summer time in several countries including in British English
British English
British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...

 and European official terminology (see Terminology)—is the practice of temporarily advancing clocks
Time zone
A time zone is a region on Earth that has a uniform standard time for legal, commercial, and social purposes. In order for the same clock time to always correspond to the same portion of the day as the Earth rotates , different places on the Earth need to have different clock times...

 during the summertime so that afternoons have more daylight
Daylight
Daylight or the light of day is the combination of all direct and indirect sunlight outdoors during the daytime. This includes direct sunlight, diffuse sky radiation, and both of these reflected from the Earth and terrestrial objects. Sunlight scattered or reflected from objects in outer space is...

 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 1895 by George Vernon Hudson
George Vernon Hudson
George Vernon Hudson was an English-born New Zealand entomologist and astronomer.Born in London, Hudson was the sixth child of Charles Hudson, an artist and stained-glass window designer. By the age of 14 he had built up a collection of British insects, and had published a paper in The Entomologist...

. Many countries have used it since then; details vary by location
Daylight saving time around the world
Daylight saving time around the world, showing usage and a short history by location in alphabetic order, grouped by continent. Most areas of North America and Europe observe daylight saving time , while most areas of Africa and Asia do not...

 and change occasionally.

The practice has been both praised and criticized. Adding daylight to afternoons benefits retailing, sports, and other activities that exploit sunlight after working hours, but causes problems for farming, evening entertainment and other occupations tied to the sun. 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, modern heating and cooling usage patterns differ greatly, and research about how DST currently affects energy use is limited or contradictory.

DST clock shifts present other challenges. They complicate timekeeping, and can disrupt meetings, travel, billing, recordkeeping, medical devices, heavy equipment, and sleep patterns. Software can often adjust computer clocks automatically, but this can be limited and error-prone, particularly when DST protocols are changed.

Origin

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
Day length
Day length, or length of day, or length of daytime, refers to the time each day from the moment the upper limb of the sun's disk appears above the horizon during sunrise to the moment when the upper limb disappears below the horizon during sunset...

, so that each daylight hour was longer during summer. For example, Roman water clock
Water clock
A water clock or clepsydra is any timepiece in which time is measured by the regulated flow of liquid into or out from a vessel where the amount is then measured.Water clocks, along with sundials, are likely to be the oldest time-measuring instruments, with the only exceptions...

s had different scales for different months of the year: at Rome's latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

 the third hour from sunrise, hora tertia, started by modern standards at 09:02 solar time
Solar time
Solar time is a reckoning of the passage of time based on the Sun's position in the sky. The fundamental unit of solar time is the day. Two types of solar time are apparent solar time and mean solar time .-Introduction:...

 and lasted 44 minutes at the winter solstice
Solstice
A solstice is an astronomical event that happens twice each year when the Sun's apparent position in the sky, as viewed from Earth, reaches its northernmost or southernmost extremes...

, but at the summer solstice it started at 06:58 and lasted 75 minutes. After ancient times, equal-length civil hours eventually supplanted unequal, so civil time
Civil time
In modern usage, civil time refers to statutory time scales designated by civilian authorities, or to local time indicated by clocks. Modern civil time is generally standard time in a time zone at a fixed offset from Coordinated Universal Time or from Greenwich Mean Time , possibly adjusted by...

 no longer varies by season. Unequal hours are still used in a few traditional settings, such as some Mount Athos
Mount Athos
Mount Athos is a mountain and peninsula in Macedonia, Greece. A World Heritage Site, it is home to 20 Eastern Orthodox monasteries and forms a self-governed monastic state within the sovereignty of the Hellenic Republic. Spiritually, Mount Athos comes under the direct jurisdiction of the...

 monasteries and all Jewish ceremonies.
During his time as an American envoy to France, Benjamin Franklin
Benjamin Franklin
Dr. Benjamin Franklin was one of the Founding Fathers of the United States. A noted polymath, Franklin was a leading author, printer, political theorist, politician, postmaster, scientist, musician, inventor, satirist, civic activist, statesman, and diplomat...

, publisher of the old English proverb, "Early to bed, and early to rise, makes a man healthy, wealthy and wise", anonymously published a letter suggesting that Paris
Paris
Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...

ians economize on candle
Candle
A candle is a solid block or cylinder of wax with an embedded wick, which is lit to provide light, and sometimes heat.Today, most candles are made from paraffin. Candles can also be made from beeswax, soy, other plant waxes, and tallow...

s by rising earlier to use morning sunlight. This 1784 satire
Satire
Satire is primarily a literary genre or form, although in practice it can also be found in the graphic and performing arts. In satire, vices, follies, abuses, and shortcomings are held up to ridicule, ideally with the intent of shaming individuals, and society itself, into improvement...

 proposed taxing shutters
Window shutter
A window shutter is a solid and stable window covering usually consisting of a frame of vertical stiles and horizontal rails...

, rationing candles, and waking the public by ringing church bells and firing cannons at sunrise. Franklin did not propose DST; like ancient Rome, 18th-century Europe did not keep precise schedules. However, this soon changed as rail
Rail transport
Rail transport is a means of conveyance of passengers and goods by way of wheeled vehicles running on rail tracks. In contrast to road transport, where vehicles merely run on a prepared surface, rail vehicles are also directionally guided by the tracks they run on...

 and communication networks came to require a standardization of time unknown in Franklin's day.

Modern DST was first proposed by the New Zealand entomologist George Vernon Hudson
George Vernon Hudson
George Vernon Hudson was an English-born New Zealand entomologist and astronomer.Born in London, Hudson was the sixth child of Charles Hudson, an artist and stained-glass window designer. By the age of 14 he had built up a collection of British insects, and had published a paper in The Entomologist...

, whose shift-work
Shift work
Shift work is an employment practice designed to make use of the 24 hours of the clock. The term "shift work" includes both long-term night shifts and work schedules in which employees change or rotate shifts....

 job gave him leisure time to collect insects, and led him to value after-hours daylight. In 1895 he presented a paper to the Wellington Philosophical Society proposing a two-hour daylight-saving shift, and after considerable interest was expressed in Christchurch
Christchurch
Christchurch is the largest city in the South Island of New Zealand, and the country's second-largest urban area after Auckland. It lies one third of the way down the South Island's east coast, just north of Banks Peninsula which itself, since 2006, lies within the formal limits of...

, New Zealand he followed up in an 1898 paper. Many publications incorrectly credit DST's proposal to the prominent English builder and outdoorsman William Willett
William Willett
William Willett , was an English builder and a tireless promoter of British Summer Time.-Biography:Willett was born in Farnham, Surrey, in the United Kingdom, and educated at the Philological School. After some commercial experience, he entered his father's building business, Willett Building...

, who independently conceived DST in 1905 during a pre-breakfast ride, when he observed with dismay how many London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

ers slept through a large part of a summer's day. An avid golf
Golf
Golf is a precision club and ball sport, in which competing players use many types of clubs to hit balls into a series of holes on a golf course using the fewest number of strokes....

er, 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. The proposal was taken up by the Liberal Member of Parliament
Member of Parliament
A Member of Parliament is a representative of the voters to a :parliament. In many countries with bicameral parliaments, the term applies specifically to members of the lower house, as upper houses often have a different title, such as senate, and thus also have different titles for its members,...

 (MP) Robert Pearce
Robert Pearce (MP)
Robert Pearce was a British Liberal Party politician. He was a Member of Parliament for all but one of the years from 1906 to 1918, and was an early advocate in Parliament of daylight saving time....

, who introduced the first Daylight Saving Bill to the House of Commons on 12 February 1908. A select committee
Select committee
A select committee is a special subcommittee of a legislature or assembly governed under a committee system, like Robert's Rules of Order. They are often investigative in nature, collecting data or evidence for a law or problem, and will dissolve immediately after they report their findings to...

 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
German Empire
The German Empire refers to Germany during the "Second Reich" period from the unification of Germany and proclamation of Wilhelm I as German Emperor on 18 January 1871, to 1918, when it became a federal republic after defeat in World War I and the abdication of the Emperor, Wilhelm II.The German...

 and its World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

 allies were the first to use DST 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. Since then, the world has seen many enactments, adjustments, and repeals.

Procedure

In a typical case 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
Standard time
Standard time is the result of synchronizing clocks in different geographical locations within a time zone to the same time rather than using the local meridian as in local mean time or solar time. Historically, this helped in the process of weather forecasting and train travel. The concept...

 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, 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
UTC+10
UTC+10 is an identifier for a time offset from UTC of +10. This time is used in:-As standard time :*Australia **Queensland*Federated States of Micronesia**Chuuk, Yap and surrounding area...

 during standard time is at UTC+11
UTC+11
UTC+11 is an identifier for a +11 hour time offset from UTC. This time is used in:-As standard time :*Federated States of Micronesia**Kosrae, Pohnpei and surrounding area*New Caledonia*Solomon Islands*Vanuatu*Russia...

 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
Lord Howe Island
Lord Howe Island is an irregularly crescent-shaped volcanic remnant in the Tasman Sea between Australia and New Zealand, directly east of mainland Port Macquarie, and about from Norfolk Island. The island is about 11 km long and between 2.8 km and 0.6 km wide with an area of...

 uses a half-hour shift. Twenty-minute and two-hour shifts have been used in the past.

Coordination strategies differ when adjacent time zones shift clocks. The European Union
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

 shifts all at once, at 01:00 UTC; for example, Eastern European Time
Eastern European Time
Eastern European Time is one of the names of UTC+02:00 time zone, 2 hours ahead of Coordinated Universal Time. It is used in some European countries that also use Eastern European Summer Time as a summer daylight saving time.- Usage :...

 is always one hour ahead of Central European Time
Central European Time
Central European Time , used in most parts of the European Union, is a standard time that is 1 hour ahead of Coordinated Universal Time . The time offset from UTC can be written as +01:00...

. Most of North America shifts at 02:00 local time, so its zones do not shift at the same time; for example, Mountain Time
Mountain Time Zone
The Mountain Time Zone of North America keeps time by subtracting seven hours from Coordinated Universal Time, also known as Greenwich Mean Time, during the shortest days of autumn and winter , and by subtracting six hours during daylight saving time in the spring, summer, and early autumn...

 can be temporarily either zero or two hours ahead of Pacific Time
Pacific Time Zone
The Pacific Time Zone observes standard time by subtracting eight hours from Coordinated Universal Time . The clock time in this zone is based on the mean solar time of the 120th meridian west of the Greenwich Observatory. During daylight saving time, its time offset is UTC-7.In the United States...

. 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
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...

 shifted on October 26. In some cases only part of a country shifts; for example, in the U.S., Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...

 and most of Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...

 do not observe DST.

Start and end dates vary with location and year. Since 1996 European Summer Time
European Summer Time
European Summer Time is the arrangement in Europe by which clocks are advanced by one hour in spring to make the most of seasonal daylight. This is done in all of the countries of Europe except Iceland which observes Greenwich Mean Time all year round, and Russia, which has two time zones in...

 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. 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. The 2007 U.S. change was part of the Energy Policy Act of 2005
Energy Policy Act of 2005
The Energy Policy Act of 2005 is a bill passed by the United States Congress on July 29, 2005, and signed into law by President George W. Bush on August 8, 2005, at Sandia National Laboratories in Albuquerque, New Mexico...

; previously, from 1987 through 2006, the start and end dates were the first Sunday in April and the last Sunday in October, and Congress
United States Congress
The United States Congress is the bicameral legislature of the federal government of the United States, consisting of the Senate and the House of Representatives. The Congress meets in the United States Capitol in Washington, D.C....

 retains the right to go back to the previous dates now that an energy-consumption study has been done.

Beginning and ending dates are the reverse in the southern hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...

. For example, mainland Chile
Time in Chile
Continental Chile is situated geographically in UTC−05.Currently, Chile uses 2 different UTC offsets at any given point in the calendar year. Since it practices daylight saving time, in total 4 time zones are used...

 observes DST from the second Saturday in October to the second Saturday in March, with transitions at 24:00 local time. 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.
Western China
Time in China
China spans across five different standard time zones, from UTC+05:00 in the west to UTC+09:00 in the east, yet since 1949 China has only had a single standard time at UTC+08:00. The time UTC+06:00 is also used unofficially in Xinjiang and Tibet...

, Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...

, Russia
Time in Russia
There are nine time zones in Russia, which currently observe times ranging from UTC+03:00 to UTC+12:00. UTC+05:00 is not used.-List of zones:Since March 2011, the time zones are as follows:-Daylight saving time:...

 and other areas skew time zones westward, in effect observing DST year-round without complications from clock shifts. For example, Saskatoon
Saskatoon
Saskatoon is a city in central Saskatchewan, Canada, on the South Saskatchewan River. Residents of the city of Saskatoon are called Saskatonians. The city is surrounded by the Rural Municipality of Corman Park No. 344....

, Saskatchewan
Saskatchewan
Saskatchewan is a prairie province in Canada, which has an area of . Saskatchewan is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, and on the south by the U.S. states of Montana and North Dakota....

, is at longitude, slightly west of center of the idealized Mountain Time Zone , but the time in Saskatchewan
Time in Saskatchewan
Most of the Province of Saskatchewan observes Central Standard Time year round. However, since the province is geographically located in the Mountain Time Zone , it is effectively on daylight saving time year round.-History:In 1912, the first law was passed that called for the use of...

 is Central Standard Time  year-round, so Saskatoon is always about 67 minutes ahead of mean solar time. Conversely, northeast India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

 and a few other areas skew time zones eastward, in effect observing negative DST. The United Kingdom and Ireland
Republic of Ireland
Ireland , described as the Republic of Ireland , is a sovereign state in Europe occupying approximately five-sixths of the island of the same name. Its capital is Dublin. Ireland, which had a population of 4.58 million in 2011, is a constitutional republic governed as a parliamentary democracy,...

 experimented with year-round DST from 1968 to 1971 but abandoned it because of its unpopularity, particularly in northern regions.

Western France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

, Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...

, 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
Nome, Alaska
Nome is a city in the Nome Census Area in the Unorganized Borough of the U.S. state of Alaska, located on the southern Seward Peninsula coast on Norton Sound of the Bering Sea. According to the 2010 Census, the city population was 3,598. Nome was incorporated on April 9, 1901, and was once the...

, is at longitude, which is just west of center of the idealized Samoa Time Zone
Samoa Time Zone
thumb|right|250px|SST is [[UTC-11]]The Samoa Time Zone observes standard time by subtracting eleven hours from Coordinated Universal Time . The clock time in this zone is based on the mean solar time of the 165th meridian west west of the Greenwich Observatory.The zone includes the U.S...

 , but Nome observes Alaska Time
Alaska Time Zone
The Alaska Time Zone observes standard time by subtracting nine hours from Coordinated Universal Time . During daylight saving time its time offset is only eight hours . The clock time in this zone is based on the mean solar time of the 135th meridian west of the Greenwich Observatory.The zone...

  with DST, so it is slightly more than two hours ahead of the sun in winter and three in summer. Double daylight saving time has been used on occasion; for example, Britain used it during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

.

DST is generally not observed near the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

, where sunrise times do not vary enough to justify it. Some countries observe it only in some regions; for example, southern Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

 observes it while equatorial Brazil does not. Only a minority of the world's population uses DST because Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

 and Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

 generally do not observe it.

Dispute over benefits and drawbacks

Willett's 1907 proposal argued that DST increases opportunities for outdoor leisure
Leisure
Leisure, or free time, is time spent away from business, work, and domestic chores. It is also the periods of time before or after necessary activities such as eating, sleeping and, where it is compulsory, education....

 activities during afternoon sunlight hours. The longer days nearer the summer solstice in high latitudes offer more room to shift daylight from morning to evening so that early morning daylight is not wasted. 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.

General agreement about the day's layout confers so many advantages that a standard DST schedule usually outranks ad hoc
Ad hoc
Ad hoc is a Latin phrase meaning "for this". It generally signifies a solution designed for a specific problem or task, non-generalizable, and not intended to be able to be adapted to other purposes. Compare A priori....

 efforts to get up earlier, even for people who personally dislike the DST schedule. 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 television broadcasts or daylight.

Energy use

DST's potential to save energy comes primarily from its effects on residential lighting, which consumes about 3.5% of electricity in the U.S. and Canada. 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. Although energy conservation
Energy conservation
Energy conservation refers to efforts made to reduce energy consumption. Energy conservation can be achieved through increased efficient energy use, in conjunction with decreased energy consumption and/or reduced consumption from conventional energy sources...

 remains an important goal, energy usage patterns have greatly changed since then, and recent research is limited and reports contradictory results. Electricity use is greatly affected by geography, climate, and economics, making it hard to generalize from single studies.
  • The U.S. Dept. of Transportation
    United States Department of Transportation
    The United States Department of Transportation is a federal Cabinet department of the United States government concerned with transportation. It was established by an act of Congress on October 15, 1966, and began operation on April 1, 1967...

     (DOT) concluded in 1975 that DST might reduce the country's electricity usage by 1% during March and April, but the National Bureau of Standards (NBS) reviewed the DOT study in 1976 and found no significant savings.
  • In 2000 when parts of Australia
    Time in Australia
    Australia uses Standard time, i.e: the same well defined time for a region. The proper names of Australia's time zones are Australian Western Standard Time , Australian Central Standard Time , and Australian Eastern Standard Time...

     began DST in late winter, overall electricity consumption did not decrease, but the morning peak load and prices increased.
  • In Western Australia
    Western Australia
    Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...

     during summer 2006–07, DST increased electricity consumption during hotter days and decreased it during cooler days, with consumption rising 0.6% overall.
  • Although a 2007 study estimated that introducing DST to Japan would reduce household lighting energy consumption, a 2007 simulation estimated that DST would increase overall energy use in Osaka
    Osaka
    is a city in the Kansai region of Japan's main island of Honshu, a designated city under the Local Autonomy Law, the capital city of Osaka Prefecture and also the biggest part of Keihanshin area, which is represented by three major cities of Japan, Kyoto, Osaka and Kobe...

     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. This is probably because DST's effect on lighting energy use is mainly noticable in residences.
  • A 2007 study found that the earlier start to DST that year had little or no effect on electricity consumption in California.
  • A 2007 study estimated that winter daylight saving would prevent a 2% increase in average daily electricity consumption in Great Britain
    Great Britain
    Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...

    . This paper was revised in October 2009 .
  • A 2008 study examined billing data in Indiana before and after it adopted DST in 2006, and concluded that DST increased overall residential electricity consumption by 1% to 4%, due mostly to extra afternoon cooling and extra morning heating; the main increases came in the fall. The overall annual cost of DST to Indiana households was estimated to be $9 million, with an additional $1.7–5.5 million for social costs due to increased pollution.
  • The U.S. Dept. of Energy
    United States Department of Energy
    The United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...

     (DOE) concluded in a 2008 report that the 2007 U.S. extension of DST saved 0.5% of electricity usage during the extended period. This report analyzed only the extension, not the full eight months of daylight saving, and did not examine the use of heating fuels.


Several studies have suggested that DST increases motor fuel consumption. The 2008 DOE report found no significant increase in motor gasoline consumption due to the 2007 U.S. extension of DST.

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. In 1984, Fortune magazine estimated that a seven-week extension of DST would yield an additional $30 million for 7-Eleven
7-Eleven
7-Eleven is part of an international chain of convenience stores, operating under Seven-Eleven Japan Co. Ltd, which in turn is owned by Seven & I Holdings Co...

 stores, and the National Golf Foundation
National Golf Foundation
The National Golf Foundation provides golf-business research and consulting services. Founded in 1936 by golf writer Herb Graffis and his brother Joe, who nearly went bankrupt in the process, its original mission was to publish authoritative research useful to investors developing the game of...

 estimated the extension would increase golf industry revenues $200 million to $300 million. A 1999 study estimated that DST increases the revenue
Revenue
In business, revenue is income that a company receives from its normal business activities, usually from the sale of goods and services to customers. In many countries, such as the United Kingdom, revenue is referred to as turnover....

 of the European Union
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

's leisure sector by about 3%. Conversely, DST can adversely affect farmers and others whose hours are set by the sun. For example, grain harvesting is best done after dew
Dew
[Image:Dew on a flower.jpg|right|220px|thumb|Some dew on an iris in Sequoia National Park]]Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening...

 evaporates, so when field hands arrive and leave earlier in summer their labor is less valuable. DST also hurts prime-time broadcast ratings, drive-ins
Drive-in theater
A drive-in theater is a form of cinema structure consisting of a large outdoor screen, a projection booth, a concession stand and a large parking area for automobiles. Within this enclosed area, customers can view movies from the privacy and comfort of their cars.The screen can be as simple as a...

 and other theaters.

Changing clocks and DST rules has a direct economic cost, entailing 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. Although it has been argued that clock shifts correlate with decreased economic efficiency, and that in 2000 the daylight-saving effect implied an estimated one-day loss of $31 billion on U.S. stock exchanges, the estimated numbers depend on the methodology and the results have been disputed.

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%, but the 1976 NBS review of the DOT study found no differences in traffic fatalities. In 1995 the Insurance Institute for Highway Safety
Insurance Institute for Highway Safety
The Insurance Institute for Highway Safety is a U.S. non-profit organization funded by auto insurers, established in 1959 and headquartered in Arlington, Virginia. It works to reduce the number of motor vehicle crashes, and the rate of injuries and amount of property damage in the crashes that...

 estimated a reduction of 1.2%, including a 5% reduction in crashes fatal to pedestrians. Others have found similar reductions. 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. It is not clear whether sleep
Sleep
Sleep is a naturally recurring state characterized by reduced or absent consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles. It is distinguished from quiet wakefulness by a decreased ability to react to stimuli, and is more easily reversible than...

 disruption contributes to fatal accidents immediately after the spring clock shifts. A correlation between clock shifts and traffic accidents has been observed in North America and the UK but not in Finland or Sweden. If this effect exists, it is far smaller than the overall reduction in traffic fatalities. A 2009 U.S. study found that on Mondays after the switch to DST, workers sleep an average of 40 minutes less, and are injured at work more often and more severely.

In the 1970s the U.S. Law Enforcement Assistance Administration
Law Enforcement Assistance Administration
The Law Enforcement Assistance Administration was a U.S. federal agency within the U.S. Dept. of Justice. It administered federal funding to state and local law enforcement agencies, and funded educational programs, research, state planning agencies, and local crime initiatives.The LEAA was...

 (LEAA) found a reduction of 10% to 13% in Washington, D.C.
Washington, D.C.
Washington, D.C., formally the District of Columbia and commonly referred to as Washington, "the District", or simply D.C., is the capital of the United States. On July 16, 1790, the United States Congress approved the creation of a permanent national capital as permitted by the U.S. Constitution....

'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". Outdoor lighting has a marginal and sometimes even contradictory influence on crime and fear of crime.

In several countries, fire safety
Fire safety
Fire safety refers to precautions that are taken to prevent or reduce the likelihood of a fire that may result in death, injury, or property damage, alert those in a structure to the presence of a fire in the event one occurs, better enable those threatened by a fire to survive, or to reduce the...

 officials encourage citizens to use the two annual clock shifts as reminders to replace batteries in smoke
Smoke detector
A smoke detector is a device that detects smoke, typically as an indicator of fire. Commercial, industrial, and mass residential devices issue a signal to a fire alarm system, while household detectors, known as smoke alarms, generally issue a local audible and/or visual alarm from the detector...

 and carbon monoxide detector
Carbon monoxide detector
A carbon monoxide detector or CO detector is a device that detects the presence of the carbon monoxide gas in order to prevent carbon monoxide poisoning. CO is a colorless and odorless compound produced by incomplete combustion. It is often referred to as the "silent killer" because it is...

s, particularly in autumn, just before the heating
HVAC
HVAC refers to technology of indoor or automotive environmental comfort. HVAC system design is a major subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer...

 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, reprogramming thermostat
Thermostat
A thermostat is the component of a control system which regulates the temperature of a system so that the system's temperature is maintained near a desired setpoint temperature. The thermostat does this by switching heating or cooling devices on or off, or regulating the flow of a heat transfer...

s, and seasonal vaccination
Vaccination
Vaccination is the administration of antigenic material to stimulate the immune system of an individual to develop adaptive immunity to a disease. Vaccines can prevent or ameliorate the effects of infection by many pathogens...

s. Locations without DST can instead use the first days of spring and autumn as reminders.

Health

DST has mixed effects on health. In societies with fixed work schedules it provides more afternoon sunlight for outdoor exercise. It alters sunlight exposure; whether this is beneficial depends on one's location and daily schedule, as sunlight triggers vitamin D
Vitamin D
Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....

 synthesis in the skin, but overexposure can lead to skin cancer
Skin cancer
Skin neoplasms are skin growths with differing causes and varying degrees of malignancy. The three most common malignant skin cancers are basal cell cancer, squamous cell cancer, and melanoma, each of which is named after the type of skin cell from which it arises...

. Sunlight strongly influences seasonal affective disorder
Seasonal affective disorder
Seasonal affective disorder , also known as winter depression, winter blues, summer depression, summer blues, or seasonal depression, is a mood disorder in which people who have normal mental health throughout most of the year experience depressive symptoms in the winter or summer, spring or autumn...

. DST may help in depression
Depression (mood)
Depression is a state of low mood and aversion to activity that can affect a person's thoughts, behaviour, feelings and physical well-being. Depressed people may feel sad, anxious, empty, hopeless, helpless, worthless, guilty, irritable, or restless...

 by causing individuals to rise earlier, but some argue the reverse. The Retinitis Pigmentosa
Retinitis pigmentosa
Retinitis pigmentosa is a group of genetic eye conditions that leads to incurable blindness. In the progression of symptoms for RP, night blindness generally precedes tunnel vision by years or even decades. Many people with RP do not become legally blind until their 40s or 50s and retain some...

 Foundation Fighting Blindness, chaired by blind sports magnate Gordon Gund
Gordon Gund
Gordon Gund is an United States businessman and professional sports owner. He is the CEO of Gund Investment Corporation. He is the former co-owner of the San Jose Sharks and former principal owner of the Cleveland Cavaliers and is currently a minority owner of the Cavaliers...

, successfully lobbied in 1985 and 2005 for U.S. DST extensions, but DST can hurt night blindness sufferers.

Clock shifts disrupt sleep and reduce its efficiency. Effects on seasonal adaptation of the circadian rhythm
Circadian rhythm
A circadian rhythm, popularly referred to as body clock, is an endogenously driven , roughly 24-hour cycle in biochemical, physiological, or behavioural processes. Circadian rhythms have been widely observed in plants, animals, fungi and cyanobacteria...

 can be severe and last for weeks. A 2008 study found that although male suicide
Suicide
Suicide is the act of intentionally causing one's own death. Suicide is often committed out of despair or attributed to some underlying mental disorder, such as depression, bipolar disorder, schizophrenia, alcoholism, or drug abuse...

 rates rise in the weeks after the spring transition, the relationship weakened greatly after adjusting for season. A 2008 Swedish study found that heart attacks were significantly more common the first three weekdays after the spring transition, and significantly less common the first weekday after the autumn transition. The government of Kazakhstan
Kazakhstan
Kazakhstan , officially the Republic of Kazakhstan, is a transcontinental country in Central Asia and Eastern Europe. Ranked as the ninth largest country in the world, it is also the world's largest landlocked country; its territory of is greater than Western Europe...

 cited health complications due to clock shifts as a reason for abolishing DST in 2005. In March 2011, Dmitri Medvedev, president of Russia, claimed that "stress of changing clocks" were the motivation for Russia to stay in DST all year long. Officials at the time talked about an annual increase in suicides.

Complexity

DST's clock shifts have the obvious disadvantage of complexity. People must remember to change their clocks; this can be time-consuming, particularly for mechanical clocks that cannot be moved backward safely. People who work across time zone
Time zone
A time zone is a region on Earth that has a uniform standard time for legal, commercial, and social purposes. In order for the same clock time to always correspond to the same portion of the day as the Earth rotates , different places on the Earth need to have different clock times...

 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 calendar day becomes variable; it is no longer always 24 hours. Disruption to meetings, travel, broadcasts, billing systems, and records management is common, and can be expensive. During an autumn transition from 02:00 to 01:00, a clock reads times from 01:00:00 through 01:59:59 twice, possibly leading to confusion.

Damage to a German steel facility occurred during a DST transition in 1993, when a computer timing system linked to a radio time synchronization signal allowed molten steel to cool for one hour less than the required duration, resulting in spattering of molten steel when it was poured. Medical devices may generate adverse events that could harm patients, without being obvious to clinicians responsible for care. These problems are compounded when the DST rules themselves change; software developers must test and perhaps modify many programs, and users must install updates and restart applications. Consumers must update devices such as programmable thermostats with the correct DST rules, or manually adjust the devices' clocks.

Some clock-shift problems could be avoided by adjusting clocks continuously or at least more gradually—for example, Willett at first 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
Standard time
Standard time is the result of synchronizing clocks in different geographical locations within a time zone to the same time rather than using the local meridian as in local mean time or solar time. Historically, this helped in the process of weather forecasting and train travel. The concept...

. For example, when reading a sundial
Sundial
A sundial is a device that measures time by the position of the Sun. In common designs such as the horizontal sundial, the sun casts a shadow from its style onto a surface marked with lines indicating the hours of the day. The style is the time-telling edge of the gnomon, often a thin rod or a...

, one must compensate for it along with time zone and natural discrepancies. Also, sun-exposure guidelines like avoiding the sun within two hours of noon become less accurate when DST is in effect.

Politics

Daylight saving has caused controversy since it began. Winston Churchill
Winston Churchill
Sir Winston Leonard Spencer-Churchill, was a predominantly Conservative British politician and statesman known for his leadership of the United Kingdom during the Second World War. He is widely regarded as one of the greatest wartime leaders of the century and served as Prime Minister twice...

 argued that it enlarges "the opportunities for the pursuit of health and happiness among the millions of people who live in this country" and pundits have dubbed it "Daylight Slaving Time". Historically, retailing, sports and tourism interests have favored daylight saving, while agricultural and evening entertainment interests have opposed it, and its initial adoption had been prompted by energy crisis
Energy crisis
An energy crisis is any great bottleneck in the supply of energy resources to an economy. In popular literature though, it often refers to one of the energy sources used at a certain time and place, particularly those that supply national electricity grids or serve as fuel for vehicles...

 and war.

The fate of Willett's 1907 proposal illustrates several political issues involved. The proposal attracted many supporters, including Balfour
Arthur Balfour
Arthur James Balfour, 1st Earl of Balfour, KG, OM, PC, DL was a British Conservative politician and statesman...

, Churchill, Lloyd George
David Lloyd George
David Lloyd George, 1st Earl Lloyd-George of Dwyfor OM, PC was a British Liberal politician and statesman...

, MacDonald
Ramsay MacDonald
James Ramsay MacDonald, PC, FRS was a British politician who was the first ever Labour Prime Minister, leading a minority government for two terms....

, Edward VII
Edward VII of the United Kingdom
Edward VII was King of the United Kingdom and the British Dominions and Emperor of India from 22 January 1901 until his death in 1910...

 (who used half-hour DST at Sandringham
Sandringham Time
Sandringham time is the name given to the idiosyncratic alterations that King Edward VII made to the timekeeping at the royal estate of Sandringham...

), the managing director of Harrods
Harrods
Harrods is an upmarket department store located in Brompton Road in Brompton, in the Royal Borough of Kensington and Chelsea, London. The Harrods brand also applies to other enterprises undertaken by the Harrods group of companies including Harrods Bank, Harrods Estates, Harrods Aviation and Air...

, and the manager of the National Bank. However, the opposition was stronger: it included Prime Minister Asquith, Christie
William Christie (astronomer)
Sir William Henry Mahoney Christie FRS was a British astronomer.He was born in Woolwich, London, the son of Samuel Hunter Christie and educated at King's College London, and at Trinity College, Cambridge...

 (the Astronomer Royal
Astronomer Royal
Astronomer Royal is a senior post in the Royal Household of the Sovereign of the United Kingdom. There are two officers, the senior being the Astronomer Royal dating from 22 June 1675; the second is the Astronomer Royal for Scotland dating from 1834....

), George Darwin
George Darwin
Sir George Howard Darwin, FRS was an English astronomer and mathematician.-Biography:Darwin was born at Down House, Kent, the second son and fifth child of Charles and Emma Darwin...

, Napier Shaw
Napier Shaw
Sir William Napier Shaw FRS, , was a British meteorologist. He introduced the air pressure unit millibar, as well as the tephigram, a diagram of temperature changes....

 (director of the Meteorological Office), many agricultural organizations, and theater owners. After many hearings the proposal was narrowly defeated in a Parliament
Parliament of the United Kingdom
The Parliament of the United Kingdom of Great Britain and Northern Ireland is the supreme legislative body in the United Kingdom, British Crown dependencies and British overseas territories, located in London...

 committee vote in 1909. Willett's allies introduced similar bills every year from 1911 through 1914, to no avail. The U.S. was even more skeptical: Andrew Peters
Andrew James Peters
Andrew James Peters was an American politician. He was born on April 3, 1872 in Jamaica Plain, a section of Boston. His family had been in Massachusetts since the first Andrew Peters arrived there in 1657. Peters attended Harvard University and Harvard Law School. He served two terms in the...

 introduced a DST bill to the U.S. House of Representatives
United States House of Representatives
The United States House of Representatives is one of the two Houses of the United States Congress, the bicameral legislature which also includes the Senate.The composition and powers of the House are established in Article One of the Constitution...

 in May 1909, but it soon died in committee.

After Germany led the way with starting DST during World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

 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. U.S. retailing and manufacturing interests led by Pittsburgh
Pittsburgh, Pennsylvania
Pittsburgh is the second-largest city in the US Commonwealth of Pennsylvania and the county seat of Allegheny County. Regionally, it anchors the largest urban area of Appalachia and the Ohio River Valley, and nationally, it is the 22nd-largest urban area in the United States...

 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.

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. The U.S. was more typical: Congress repealed DST after 1919. President Woodrow Wilson
Woodrow Wilson
Thomas Woodrow Wilson was the 28th President of the United States, from 1913 to 1921. A leader of the Progressive Movement, he served as President of Princeton University from 1902 to 1910, and then as the Governor of New Jersey from 1911 to 1913...

, like Willett an avid golfer, vetoed the repeal twice but his second veto was overridden. Only a few U.S. cities retained DST locally thereafter, including New York so that its financial exchanges could maintain an hour of arbitrage
Arbitrage
In economics and finance, arbitrage is the practice of taking advantage of a price difference between two or more markets: striking a combination of matching deals that capitalize upon the imbalance, the profit being the difference between the market prices...

 trading with London, and Chicago and Cleveland to keep pace with New York. Wilson's successor Warren G. Harding
Warren G. Harding
Warren Gamaliel Harding was the 29th President of the United States . A Republican from Ohio, Harding was an influential self-made newspaper publisher. He served in the Ohio Senate , as the 28th Lieutenant Governor of Ohio and as a U.S. Senator...

 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
Washington, D.C.
Washington, D.C., formally the District of Columbia and commonly referred to as Washington, "the District", or simply D.C., is the capital of the United States. On July 16, 1790, the United States Congress approved the creation of a permanent national capital as permitted by the U.S. Constitution....

 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.

Since Germany's adoption in 1916 the world has seen many enactments, adjustments, and repeals of DST, with similar politics involved. The history of time in the United States includes DST during both world wars, but no standardization of peacetime DST until 1966. In the mid-1980s, Clorox
Clorox
The Clorox Company is a US-based manufacturer of various food and chemical products based in Oakland, California, which is best known for its bleach product, Clorox.- History :...

 (parent of Kingsford Charcoal
Kingsford (charcoal)
Kingsford is a brand of charcoal used for grilling, along with related products. The brand is owned by The Clorox Company.The Kingsford Company was formed by Henry Ford and E.G. Kingsford during the early 1920s. Charcoal was developed from Ford Motor Company's factory waste wood scrap. The...

) and 7-Eleven
7-Eleven
7-Eleven is part of an international chain of convenience stores, operating under Seven-Eleven Japan Co. Ltd, which in turn is owned by Seven & I Holdings Co...

 provided the primary funding for the Daylight Saving Time Coalition behind the 1987 extension to U.S. DST, and both Idaho
Idaho
Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....

 senators
United States Senate
The United States Senate is the upper house of the bicameral legislature of the United States, and together with the United States House of Representatives comprises the United States Congress. The composition and powers of the Senate are established in Article One of the U.S. Constitution. Each...

 voted for it based on the premise that during DST fast-food restaurants sell more French fries, which are made from Idaho potatoes. 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. In 2005, the Sporting Goods Manufacturers Association
Sporting Goods Manufacturers Association
The Sporting Goods Manufacturing Association is a trade association of the retailers, manufacturers and marketers of the sporting goods industry. The SGMA was founded in 1906 in New York, and is currently based in Washington, D.C. Currently, the SGMA represents over 1,000 manufacturers, retailers...

 and the National Association of Convenience Stores
National Association of Convenience Stores
NACS is an international trade association representing the convenience and fuel retailing industry.-Background:NACS was founded August 14, 1961, as the National Association of Convenience Stores. It is an international trade association representing more than 2,100 retail and 1,500 supplier...

 successfully lobbied for the 2007 extension to U.S. DST. In December 2008, the Daylight Saving for South East Queensland
Daylight Saving for South East Queensland
Daylight Saving for South East Queensland is a political party in Queensland, Australia. It is a single-issue party, run by volunteers, which advocates the implementation of a dual-time zone arrangement for Daylight Saving in South East Queensland while the remainder of the state maintains...

(DS4SEQ) political party
Political party
A political party is a political organization that typically seeks to influence government policy, usually by nominating their own candidates and trying to seat them in political office. Parties participate in electoral campaigns, educational outreach or protest actions...

 was officially registered in Queensland, advocating the implementation of a dual-time zone
Time zone
A time zone is a region on Earth that has a uniform standard time for legal, commercial, and social purposes. In order for the same clock time to always correspond to the same portion of the day as the Earth rotates , different places on the Earth need to have different clock times...

 arrangement for Daylight Saving in South East Queensland
South East Queensland
South East Queensland is a region of the state of Queensland in Australia, which contains approximately two-thirds of the state population...

 while the rest of the state maintains standard time
Standard time
Standard time is the result of synchronizing clocks in different geographical locations within a time zone to the same time rather than using the local meridian as in local mean time or solar time. Historically, this helped in the process of weather forecasting and train travel. The concept...

. DS4SEQ contested the March 2009 Queensland State election
Queensland state election, 2009
The Queensland state election was held to elect members to the unicameral Parliament of Queensland on 21 March 2009. The election saw the incumbent Labor government led by Premier Anna Bligh defeat the Liberal National Party of Queensland led by Opposition Leader Lawrence Springborg, and gain a...

 with 32 candidates and received one percent of the state-wide primary vote, equating to around 2.5% across the 32 electorates contested. After a three-year trial, more than 55% of Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...

ns voted against DST in 2009, with rural areas strongly opposed. On 14 April 2010, after being approached by the DS4SEQ political party, Queensland Independent member Peter Wellington
Peter Wellington
Peter Wellington is an Independent member of the Queensland Legislative Assembly, for the Electoral district of Nicklin. Wellington, along with fellow independent Liz Cunningham, briefly held the balance in power following the 1998 state election...

, introduced the Daylight Saving for South East Queensland Referendum Bill 2010
Daylight Saving for South East Queensland Referendum Act 2010
The Daylight Saving for South East Queensland Referendum Bill 2010 was tabled in Queensland Parliament on 14 April 2010, by Queensland, Independent Member Peter Wellington. Wellington has called for a referendum to be held at the next State election on introduction of daylight saving time for...

 into Queensland Parliament, calling for a referendum
Referendum
A referendum is a direct vote in which an entire electorate is asked to either accept or reject a particular proposal. This may result in the adoption of a new constitution, a constitutional amendment, a law, the recall of an elected official or simply a specific government policy. It is a form of...

 to be held at the next State election on the introduction of daylight saving into South East Queensland
South East Queensland
South East Queensland is a region of the state of Queensland in Australia, which contains approximately two-thirds of the state population...

 under a dual-time zone
Time zone
A time zone is a region on Earth that has a uniform standard time for legal, commercial, and social purposes. In order for the same clock time to always correspond to the same portion of the day as the Earth rotates , different places on the Earth need to have different clock times...

 arrangement. The Bill was defeated in Queensland Parliament on 15 June 2011.

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.

The 2011 declaration by Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

 that it would not turn its clocks back was subsequently followed by a similar declaration from Belarus
Belarus
Belarus , officially the Republic of Belarus, is a landlocked country in Eastern Europe, bordered clockwise by Russia to the northeast, Ukraine to the south, Poland to the west, and Lithuania and Latvia to the northwest. Its capital is Minsk; other major cities include Brest, Grodno , Gomel ,...

.

Terminology

Although daylight saving time is considered to be correct, daylight savings time is commonly used. The 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. The common variants daylight savings time and daylight savings use savings by analogy to savings account
Savings account
Savings accounts are accounts maintained by retail financial institutions that pay interest but cannot be used directly as money . These accounts let customers set aside a portion of their liquid assets while earning a monetary return...

. Daylight time is also common. Willett's 1907 proposal used the term daylight saving, but by 1911 the term summer time replaced daylight saving time in draft legislation in Britain, and continental Europe uses similar phrases, such as Sommerzeit in Germany, zomertijd in Dutch, horario de verano or hora de verano in Spain and l'heure d'été in France, whereas in Italy the term is ora legale, that is, legal time (legally enforced time) as opposed to "ora solare", solar time, in Winter.

The name of local time typically changes when DST is observed. American English
American English
American English is a set of dialects of the English language used mostly in the United States. Approximately two-thirds of the world's native speakers of English live in the United States....

 replaces standard with daylight: for example, Pacific Standard Time
Pacific Time Zone
The Pacific Time Zone observes standard time by subtracting eight hours from Coordinated Universal Time . The clock time in this zone is based on the mean solar time of the 120th meridian west of the Greenwich Observatory. During daylight saving time, its time offset is UTC-7.In the United States...

(PST) becomes Pacific Daylight Time (PDT). British English
British English
British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...

 calls UK time British Summer Time
British Summer Time
Western European Summer Time is a summer daylight saving time scheme, 1 hour ahead of Coordinated Universal Time. It is used in the following places:* the Canary Islands* Portugal * Ireland...

(BST), and typically inserts summer into other time zones, e.g. Central European Time
Central European Time
Central European Time , used in most parts of the European Union, is a standard time that is 1 hour ahead of Coordinated Universal Time . The time offset from UTC can be written as +01:00...

(CET) becomes Central European Summer Time
Central European Summer Time
Central European Summer Time is one of the names of the Daylight saving time offset using the UTC offset of UTC+02:00, 2 hours ahead of Coordinated Universal Time. It is used as a summer daylight saving time in most European countries. During the winter, Central European Time is used...

(CEST). Abbreviations do not always change: for example, many (though not all) Australians say that Eastern Standard Time
Time in Australia
Australia uses Standard time, i.e: the same well defined time for a region. The proper names of Australia's time zones are Australian Western Standard Time , Australian Central Standard Time , and Australian Eastern Standard Time...

(EST) becomes Eastern Summer Time (also EST). In Australia it is also called EDT (Eastern Daylight Time)

The American English mnemonic
Mnemonic
A mnemonic , or mnemonic device, is any learning technique that aids memory. To improve long term memory, mnemonic systems are used to make memorization easier. Commonly encountered mnemonics are often verbal, such as a very short poem or a special word used to help a person remember something,...

 "spring
Spring (season)
Spring is one of the four temperate seasons, the transition period between winter and summer. Spring and "springtime" refer to the season, and broadly to ideas of rebirth, renewal and regrowth. The specific definition of the exact timing of "spring" varies according to local climate, cultures and...

 forward, fall
Autumn
Autumn is one of the four temperate seasons. Autumn marks the transition from summer into winter usually in September or March when the arrival of night becomes noticeably earlier....

 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.

Computing

Changes to DST rules cause problems in existing computer installations. For example, the 2007 change to DST rules in North America required many computer systems to be upgraded, with the greatest impact on email and calendaring programs; the upgrades consumed a significant effort by corporate information technologists
Information technology
Information technology is the acquisition, processing, storage and dissemination of vocal, pictorial, textual and numerical information by a microelectronics-based combination of computing and telecommunications...

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

Many systems in use today base their date/time calculations from data derived from zoneinfo
Zoneinfo
The tz database, also called the zoneinfo database or IANA Time Zone Database, is a collaborative compilation of information about the world's time zones, primarily intended for use with computer programs and operating systems. It is sometimes referred to as the Olson database after the founding...

, which is sometimes known as tzdata.

tz database

The tz 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
Unix-like
A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....

 operating systems, Java
Java (Sun)
Java refers to several computer software products and specifications from Sun Microsystems, a subsidiary of Oracle Corporation, that together provide a system for developing application software and deploying it in a cross-platform environment...

, Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

 and Oracle
Oracle Database
The Oracle Database is an object-relational database management system produced and marketed by Oracle Corporation....

; HP
Hewlett-Packard
Hewlett-Packard Company or HP is an American multinational information technology corporation headquartered in Palo Alto, California, USA that provides products, technologies, softwares, solutions and services to consumers, small- and medium-sized businesses and large enterprises, including...

's "tztab" database is similar but incompatible. When temporal authorities change DST rules, zoneinfo updates are installed as part of ordinary system maintenance. In Unix-like systems the TZ environment variable
Environment variable
Environment variables are a set of dynamic named values that can affect the way running processes will behave on a computer.They can be said in some sense to create the operating environment in which a process runs...

 specifies the location name, as in TZ=':America/New_York'. On Linux however there is a system-wide setting that is applied if the TZ environment variable isn't set, this setting is controlled by the contents of the /etc/localtime file, which is usually a symlink or hardlink to one of the zoneinfo files. Internal time is stored in timezone-independent epoch time; the TZ is used by each of potentially many simultaneous users and processes to independently localize time display.

Older or stripped-down systems may support only the TZ values required by POSIX
POSIX
POSIX , an acronym for "Portable Operating System Interface", is a family of standards specified by the IEEE for maintaining compatibility between operating systems...

, 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 timestamps.

Microsoft Windows

As with zoneinfo, a user of Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

 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. Windows Vista
Windows Vista
Windows Vista is an operating system released in several variations developed by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs, and media center PCs...

 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.

These limitations have caused problems. For example, before 2005, DST in Israel
Israel
The State of Israel is a parliamentary republic located in the Middle East, along the eastern shore of the Mediterranean Sea...

 varied each year and was skipped some years. Windows 95
Windows 95
Windows 95 is a consumer-oriented graphical user interface-based operating system. It was released on August 24, 1995 by Microsoft, and was a significant progression from the company's previous Windows products...

 used rules correct for 1995 only, causing problems in later years. In Windows 98
Windows 98
Windows 98 is a graphical operating system by Microsoft. It is the second major release in the Windows 9x line of operating systems. It was released to manufacturing on 15 May 1998 and to retail on 25 June 1998. Windows 98 is the successor to Windows 95. Like its predecessor, it is a hybrid...

 Microsoft marked Israel as not having DST, forcing Israeli users to shift their computer clocks manually twice a year. The 2005 Israeli Daylight Saving Law
Israeli Daylight Saving Law
Israel Summer Time , also in English, Israel Daylight Time is the practice in Israel by which clocks are advanced by one hour around Passover to make the most of seasonal daylight. Since 2005, this period extends every year from 2:00 a.m. on the last Friday before April 2, i.e...

 established predictable rules using the Jewish calendar 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 and a Microsoft tool that switches zones automatically.

Microsoft Windows keeps the system real-time clock
Real-time clock
A real-time clock is a computer clock that keeps track of the current time. Although the term often refers to the devices in personal computers, servers and embedded systems, RTCs are present in almost any electronic device which needs to keep accurate time.-Terminology:The term is used to avoid...

 in local time. This causes several problems, including compatibility when multi booting with operating systems that set the clock to UTC, and double-adjusting the clock when multi booting different Windows versions, such as with a rescue boot disk. This approach is a problem even in Windows-only systems: there is no support for per-user timezone settings, only a single system-wide setting. In 2008 Microsoft hinted that future versions of Windows will partially support a Windows registry
Windows registry
The Windows Registry is a hierarchical database that stores configuration settings and options on Microsoft Windows operating systems. It contains settings for low-level operating system components as well as the applications running on the platform: the kernel, device drivers, services, SAM, user...

 entry RealTimeIsUniversal that had been introduced many years earlier, when Windows NT
Windows NT
Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix. It was intended to complement...

 supported RISC machines with UTC clocks, but had not been maintained since.

An interesting effect can be observed with file time properties. The NTFS
NTFS
NTFS is the standard file system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Server 2003, Windows Server 2008, Windows Vista, and Windows 7....

 file system used by recent versions of Windows stores the file with a UTC time stamp, but displays it corrected to local—or seasonal—time. However, the FAT
File Allocation Table
File Allocation Table is a computer file system architecture now widely used on many computer systems and most memory cards, such as those used with digital cameras. FAT file systems are commonly found on floppy disks, flash memory cards, digital cameras, and many other portable devices because of...

 filesystem commonly used on removable devices stores only the local time. Consequently, when a file is copied from the hard disk onto separate media, its time will be set to the current local time. If the time adjustment is changed, perhaps automatically (daylight saving) or if the user selects a different time zone, then when the timestamps of the original file and the copy are compared there will be a difference. This may be verified (without having to wait for the next equinox) by copying a file, removing the media, adjusting the time zone options, reconnecting the media, and viewing the details of the file and its copy. The same effect can be observed when compressing and uncompressing files with some file archiver
File archiver
A file archiver is a computer program that combines a number of files together into one archive file, or a series of archive files, for easier transportation or storage...

s. This effect needs to be in mind when trying to determine if a file is a duplicate of another although there are other methods of comparing files for equality like using checksum
Md5sum
md5sum is a computer program that calculates and verifies 128-bit MD5 hashes, as described in RFC 1321. The MD5 hash functions as a compact digital fingerprint of a file. As with all such hashing algorithms, there is theoretically an unlimited number of files that will have any given MD5 hash...

 algorithms
Checksum
A checksum or hash sum is a fixed-size datum computed from an arbitrary block of digital data for the purpose of detecting accidental errors that may have been introduced during its transmission or storage. The integrity of the data can be checked at any later time by recomputing the checksum and...

.

External links

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