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Daylight saving time

Daylight saving time (also called DST, or Summer Time) is the local time a country adopts for a portion of the year, usually an hour forward from its standard official time.

It is a system intended to "save" daylight (as opposed to wasting it by, say, sleeping while the sun shines). The official time is adjusted forward during the spring and summer months, so that the active hours of work and school will better match the hours of daylight.

Locations that observe or do not observe DST are listed in the article Time zone#List of time zones and contained areas.

Table of contents
1 Origin
2 History
3 Criticism of DST
4 DST around the world
5 Mnemonic
6 See also
7 External Links


It is sometimes asserted that DST was first proposed by Benjamin Franklin in a letter to the editors of the Journal of Paris [1]. However, the article was humorous; Franklin was not proposing DST, but rather that people should get up and go to bed earlier.

It was first seriously proposed by William Willett in the "Waste of Daylight" [1], published in 1907, but he was unable to get the British government to adopt it despite considerable lobbying.


The idea of daylight saving time was first put into practice by the German government during the First World War between the 30th of April, 1916 and the 1st of October, 1916. Shortly afterwards, the United Kingdom followed suit, first adopting DST between the 21st of May, 1916 and the 1st of October, 1916. Then on March 19, 1918 the United States Congress established several time zones (which were already in use by railroads since 1883) and made daylight saving time official (which went into effect on March 31) for the remainder of World War I. It was observed for seven months in 1918 and 1919. The law, however, proved so unpopular (mostly because people rose earlier and went to bed earlier than in modern times) that the law was later repealed.

Daylight saving time was reinstated in the United States on February 9, 1942, again as a wartime measure to conserve resources, this time in order to fight World War II. This remained in effect until the war began winding down and the requirement was removed on September 30, 1945. From 1945 to 1966, there was no federal law about daylight saving time. States and localities were free to observe daylight saving time or not. The Uniform Time Act of 1966 created daylight saving time to begin on the last Sunday of April and to end on the last Sunday of October. Any area that wanted to be exempt from daylight saving time could do so by passing a local ordinance. The law was amended in 1986 to begin daylight saving time on the first Sunday in April.

Criticism of DST

DST is not universally accepted; many localities do not observe it. Nevertheless, proponents claim that DST helps more than it hurts. The primary claim is that it reduces energy consumption. Opponents claim that there's not enough benefit to justify needing to adjust clocks twice per year. The disruption in sleep patterns associated with setting clocks forward, and thereby "losing" an hour, correlates with a spike in the number of severe auto accidents.

Campaigners in Britain would like the country to stay on British Summer Time (BST) all year round, or in other words, adopt Central European Time and abolish BST. Alternatively, some would like Britain to adopt Central European Time and jump forward another hour during the summer (adopting a Single/Double Summer Time from Britain's perspective). This would make winter evenings longer, thereby reducing traffic accidents and cases of seasonal affective disorder. Opponents point to the longer hours of darkness on winter mornings, especially in Scotland, which might well cause an increase in road accidents. It has even been suggested that Scotland should be placed on a different time zone from the rest of the UK, which does not seem likely to occur in the foreseeable future.

DST is particularly unpopular among people working in agriculture because the animals do not observe it, and thus the people are placed out of synchronization with the rest of the community, including school times, broadcast schedules, and the like.

DST is a long-standing controversy in Indiana, not only as an agricultural state, but also because the meridian separating the eastern and central time zones divides the state. In the past, neighboring communities sometimes ended up one or even two hours apart. In the current compromise, the state has three kinds of time zone: 77 counties, most of the state, are on Eastern Standard Time but do not use DST; 7 counties near Chicago and 3 counties in the southwestern corner of the state are on Central Standard Time and do use DST; and 2 counties near Cincinnati, Ohio and 3 counties near Louisville, Kentucky are on Eastern Standard time but do use DST.

DST around the world

For fairly obvious reasons, DST is a temperate zone practice: day lengths in the tropics do not vary enough to justify DST. Hawaii, the only U.S. state in the tropics, does not observe DST. However, Mexico has adopted DST nationwide, even in its tropical regions, because of its increasing economic ties to the U.S. The Mexican state of Sonora does not observe DST because it borders on a U.S. state that also does not observe DST (Arizona).

The amount of the time shift varies, but one hour is the most common. The dates of the beginning and ending of DST also vary, but it commonly begins in the Northern Hemisphere at 2:00 AM on either the first Sunday in April or the last Sunday in March, and ends at 2:00 AM on the last Sunday in October. In the Southern Hemisphere, the beginning and ending dates are switched (thus the time difference between e.g. the UK and Chile may be 3, 4 or 5 hours).

North America generally follows the same procedure, going by local time in each zone, each time zone switching at 2am LST (local standard time) to 3am LDT on the first Sunday in April, and again from 2am LDT to 1am LST on the last Sunday in October.

All countries in Europe, except Iceland, Greenland and the Azores, observe DST and switch at the same universal time (1:00 UTC) in all five zones, going from 10pm/0/1/2/3am LST to 11pm/1/2/3/4am LDT simultaneously on the last Sunday in March, and back from 11pm/1/2/3/4am LDT to 10pm/0/1/2/3am LST on the last Sunday in October (formerly September), like in the USA (for the European Union, except the overseas territories, per EU directive 2000/84/EC [1]; for Greenland: the Saturday before)).

Australia has had mixed implementation of Daylight Savings. Normally divided into three time zones, during Daylight Savings there are five distinct time zones ranging from UTC+8 to UTC+11. Despite several referenda on the topic, Western Australia, the Northern Territory and Queensland still refuse to adopt the practice.

Cuba always starts on April 1 however, but keeps the same ending date.

The expression daylight savings time (with the extra "s") is a common alternate form, but considered a usage error by some.


The mnemonic "spring forward, fall back" tells us how to reset clocks when the time changes, regardless of hemisphere. ("Fall" being the old British English, and a current American English, word for autumn).

See also

External Links