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(originally published to Helium writing site, now gone; written in 2008, updated in 2013)

About 70 countries around the world use daylight saving time (DST), advancing their clocks one hour in the spring and turning them back in autumn. Changeover time in most countries is the wee small hours of Sunday morning, which causes the least disruption to businesses and households alike.

Virtually all European countries have daylight saving time. The European Community countries now have coordinated DST, starting on the last Sunday in March since 1981 and ending on the last Sunday in October since 1998. The only country not to use it is Iceland where it gets dark so late and light so early in summer that DST would be of limited use. Iceland last had DST in 1967.

Most of Europe had DST during World War I, especially Western Europe. DST finished in many European countries after 1919 or 1920, although some kept it through the entire interwar period, such as the United Kingdom, France, Netherlands, Belgium and Luxembourg, as did parts of Canada and the United States. Nearly all of Europe adopted DST during World War II, some not turning back their clocks at all for several years. Two hours of daylight saving in summer, called double daylight saving time, and one hour in winter was common practice. Daylight saving time was often called War Time during this period. Various countries in other parts of the world had DST during World War II.

After the war, some countries stopped DST, although a number continued with it for a few years before abandoning it.  The only places to have had DST in the entire postwar period are parts of the United States and Canada. No European country has had it throughout this period. The closest is the United Kingdom, which has had it in all years except 1968-1971 when it switched to Central European Time (GMT+1) and consequently didn’t have separate DST. A large number of countries resumed daylight saving time in the 1970s and early 1980s, especially at the time of the energy crises.

In the United States, DST was a state and local issue, with the result that some areas had it and other didn’t. During a train or road trip of a few hours, a person could pass through a number of different time zones. There were even instances of people living on opposite sides of a river being on different times. This caused various problems when family members went to work or school or the shops on the other side of the river. On one occasion, different workers in a single building were on two separate times, as some businesses recognised DST and others didn’t. A similar problem still happens at the southern end of Australia’s Gold Coast area where the state of New South Wales has DST but the state of Queensland doesn’t have it.

Daylight saving time became a federal issue in the United States in 1966 with the Uniform Time Act. Since then, nearly all states have had DST. Exceptions are Arizona except the Navajo Nation, and Hawaii. The only occasion Hawaii had DST was in 1933, for three weeks from 30 April to 21 May, although some sources say it lasted just one day and was abandoned on 1 May. DST is less useful in tropical areas as day and night are of similar length. Indiana has observed DST since 2006. In Alaska and Florida, there are moves to try and end DST. The period of DST each year in the United States was extended by a month under the Energy Policy Act of 2005. It now lasts almost two-thirds of the year, from the second Sunday in March to the first Sunday in November.

All of Canada except Saskatchewan province observes DST, including those areas within the Arctic Circle where daylight lasts 24 hours for at least part of the summer. The whole of Saskatchewan moved to the Central time zone in 1966, which effectively means it has year round DST. Similarly, time zone boundaries for many countries have changed considerably over the years and are still occurring. Most changes tend to be in a easterly direction and are often for the purpose of saving daylight. This results in a skewing of zones and is evident in places like the United States, Canada, southern South America, Western Europe, parts of Africa, as well as Russia, China and Mongolia. On top of this, most of these places also have DST, although China stopped in 1991 and Mongolia in 2006.

While the use or non-use of DST is quite settled in Europe and North America, this isn’t the case in Asia. About seven Asian countries currently observe DST. Iran had it from 1978 to 1980 and from 1991 to 2005, and again from 2008. Iraq used it from 1982 to 2007. Israel had DST for most of the period 1940 to 1957, 1974, 1975, and all years since 1985. At the end of DST, until 2012 clocks were moved back on the Sunday between the two holy days of Rosh Hashanah and Yom Kippur, whose dates differ each year. From 2013, clocks go back on the last Sunday in October. Georgia had DST in World War II and for most years since 1981, until 2004. Japan only used it from 1948 to 1951 but moves to resurrect it have gained momentum since the late 1990s. South Korea has hardly used DST either. Taiwan hasn’t used it since 1980. Many of the previous USSR countries have abandoned it. Pakistan had it in 2002, 2008 and 2009 due to high fuel costs.

Mexico observed DST during World War II. The whole country, including its tropical areas, has had DST since 1996, except Sonara from 1999 due to its trade with Arizona. Baja California has had it for several decades. In Central America, most countries have used it at some stage, although none use it at the moment. Guatemala and Nicaragua have had it sporadically since 1973, when energy conservation demands it. In the West Indies, the Bahamas and Cuba have used DST since the mid 1960s.

In South America, Argentina and Brazil have opted in and then out of DST six and five times respectively. Some states in Brazil have used it each year since 1985, while certain Argentinian provinces resumed it in 2007 to 2009. Uruguay has the world record for the most episodes of DST with eleven: 1923-24 to 1925-26, 1933-34 to 1938-39, 1939-40 to 1942-43, 1959-1960, 1965-1970, 1972, 1974-1976, 1977-78, 1979-80, 1987-88 to 1992-93, and 2004-05 to present. This country narrowly shades Portugal who has had ten episodes of DST. Energy saving considerations play a major role in most of these countries. Other South American countries currently using DST include Chile and Paraguay.

Most of Africa doesn’t observe DST and it is the only continent where most countries have never adopted it. Egypt had it during World War II and again from 1957 until 2010. Algeria used it in both world wars and for a few odd years in the 1970s. Libya has had it on and off, including from 2012. Namibia has had it since 1994 and Morocco since 2008. A handful of other African countries have had DST for a period before abandoning it. South Africa used it for two years in the 1940s but not since.

In Australia, Tasmania started DST in 1916. The rest had it in 1917, for a few years in World War II and, in most states, since 1971. Western Australia underwent a trial period of DST from 2006-07 to 2008-09, but hasn’t continued with it. Queensland hasn’t observed DST since 1992, although it comes up as a political issue every spring. Most residents in the state’s populated south-east want it while the rest don’t. New Zealand has had it every year since 1974-75. Fiji used it in 1998-2000 and since 2009, and Samoa since 2011. DST is used in Antarctica by certain stations if their home country has it.

In summary, nearly all of Europe observes daylight saving time whereas usage varies elsewhere. It is less common in tropical areas where day and night don’t vary much in length or in high latitude regions where summer nights are very short. A large number of countries have started and then finished DST a number of times, or tend to experiment with it, often when energy costs rise. It remains a contentious issue in many parts of the world.

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