■ Daylight Savings Time

2021. 3. 14. 02:00ㆍ■ 국제/CANADA

■ 2021년 3월 14일 오전 2시를 오전 3시로-CanaDA Daylight Savings Time 

 

일광 절약 시간제(日光節約時間制, 미국 영어: Daylight saving time, DST) 또는 서머 타임(영국 영어: summer time)은 하절기에 표준시를 원래 시간보다 한 시간 앞당긴 시간을 쓰는 것을 말한다. 즉, 0시에 일광 절약 시간제를 실시하면 1시로 시간을 조정해야 하는 것이다. 실제 낮 시간과 사람들이 활동하는 낮 시간 사이의 격차를 줄이기 위해 사용한다. 여름에는 일조 시간이 길므로 활동을 보다 일찍 시작하여 저녁 때 직장이나 학교에서 이렇게 '절약된 낮 시간'을 더 밝은 상태에서 오후에 활동할 수 있게 하는 효과가 있으며, 또한 직장이나 학교에서의 조명과 연료 등의 절감 효과를 기대할 수 있기 때문이다. 온대 지역에서는 계절에 따른 일조량의 차이가 크므로 일광 절약 시간제는 보통 온대 지역에서 시행된다.

여러 정부는 일광 절약 시간제를 특히 낮시간의 효율적인 사용을 통한 에너지 절약의 효과를 앞세우며 홍보한다. '깨어 있는 시간'을 조절함으로써 전기 조명의 사용을 절약할 수 있다는 것이다. 하지만 일광절약시간제를 반대하는 사람들은 이 주장이 근거가 없다고 반박한다. 소위 "일광절약" 기간 동안 냉방수요를 증가시켜 전반적으로 에너지를 낭비하도록 하기 때문이다.[1] (#에너지 사용에 대한 영향 참조.)

일광절약 시간제는 수면시간을 연중 두 차례나 인위적으로 조정하기 때문에, 교통사고 및 사망 증가, 수면의 질 및 건강의 악화, 인지능력 훼손 및 업무생산성 저하 등 인간행동에 부정적인 영향을 미친다.[2] (#인간행동에 대한 영향 참조.)

일광 절약 시간제는 통상 봄에서 가을까지(3월 중순 ~ 11월 초) 계속되므로 서머 타임의 '서머'(여름)라는 말에는 어폐가 있으나, 영국을 비롯한 유럽 지역에서는 서머 타임이란 말을 더 많이 사용한다.

목차

역사[편집]

1784년 미국의 벤저민 프랭클린은 여름에 더 일찍 일어남으로써 보다 경제적으로 오전 시간을 이용할 수 있으며, 따라서 밤에는 더 적은 양의 초가 소모될 것이라는 발상을 내었다. 하지만 벤자민 프랭클린은 시계를 조절하자고 주장한 것은 아니었다. 최초로 일광절약시간의 개념이 등장한 것은 1905년에 윌리엄 윌렛에 의해서였다. 그는 야외 활동을 무척 좋아하던 건설업자였는데, 이러한 발상으로 보다 효율적으로 골프를 즐길 수 있을 것이라고 생각했다. 2년 뒤에 그는 이 발상을 출판하고, 발포어와 처칠, 로이드 조지, 에드워드 7세 등의 지원을 받을 수 있었다. 하지만 당시 수상이던 아스퀴스는 반대하였다. 이후 윌렛과 그의 동지들은 1911년부터 1914년까지 계속 이 안건을 상정하였다. 제1차 세계 대전 중에 일광절약시간은 전쟁 중에 연료를 절약하고 공습을 대비하기 위한 목적으로 이용되었다. 한편 영국의 적이었던 독일도 이 발상을 받아들여 유럽 최초로 1916년 4월 30일부터 실시하였다. 영국은 1916년 5월 21일에 처음 실시하였으며, 러시아와 다른 유럽 국가들은 이듬해에 잇따라 시행했다. 오스트레일리아와 캐나다도 따르려 했으나 이들 지역의 농부들에게 이 생각은 그다지 인기가 없었다. 또한 전쟁이 끝나자 많은 나라들이 일광절약시간을 폐지하였다. 미국은 1918년 3월의 마지막 일요일부터 10월의 마지막 일요일까지 일광 절약 시간을 실시하였으나, 1919년 이후에는 의회에서 이를 폐지하였다. 이후 또 한 명의 골프광이었던 우드로 윌슨 대통령이 다시 실시하게 하였다.

 

이란[편집]

이란은 국가 최대의 명절인 누루즈부터 6개월간 일광 절약 시간제를 적용한다. 매 평년 3월 22일 0시부터 9월 21일 24시까지 적용한다. 다만, 윤년에는 3월 21일 0시부터 9월 20일 24시까지 적용한다.

북미[편집]

미국과 캐나다는 2006년까지 각 시간대의 지역시간 기준으로 4월의 첫 일요일 오전 2시에 시작하여 각 시간대의 지역 시간 기준으로 10월의 마지막 일요일 오전 2시에 해제하였으나, CST 지역은적용되지 않는다. 미국과 캐나다는 2007년부터 일광절약시간제 기간이 늘어나 각 시간대의 지역 시간 기준으로 3월의 두 번째 일요일의 오전 2시에 시작하여 각 시간대의 지역 시간 기준으로 11월 첫 일요일 오전 2시에 해제하도록 바뀌었다. 유럽은 동시에 일괄적으로 바뀌는 데 비해 미국은 시간대 별로 바뀌는 시간이 잇달아 일어나는 것이 특징이다. 이러한 변경은 43대 미국의 대통령인 조지 W. 부시 대통령이 2005년에 서명한 에너지 정책법(2005년 8월 8일)에 따른 것이다.[3]

미국과 캐나다에서 이러한 일광 절약 시간제를 따르지 않는 지역도 있다. 하와이주, 미국령 사모아, 괌, 푸에르토리코, 버진 아일랜드, 애리조나주, 인디애나주와 캐나다의 서스캐처원주 등이 그러하다. 그러나 애리조나주 지역에서 나바호족 자치지역은 일광절약시간제를 따르기도 한다. 또한 일광 절약 시간제 때문에 시간을 바꾸어야 하는 미국 사람들에게, 소방서에서는 이때 화재 경보기의 배터리를 교환할 것을 권유하는 시기로 활용하고 있다.

멕시코는 원래 써머 타임을 적용하지 않았으나, 비교적 최근에 적용한 국가이다.

남반구[편집]

남반구는 북반구 지역의 겨울 동안에 일광 절약 시간제를 시행한다.

호주는 10월의 첫 일요일 오전 2시에 시작하여 다음해 4월의 첫 일요일 오전 3시에 해제한다. 시행 지역은 뉴사우스웨일스 주(NSW), 빅토리아 주(VIC), 사우스 오스트레일리아 주(SA), 테즈메이니아 주(TAS), 오스트레일리아 수도 준주(ACT)이다.[4]

뉴질랜드는 9월의 마지막 일요일 오전 2시에 시작하여 다음해 4월 첫 번째 일요일 오전 3시에 해제한다.

브라질은 10월의 세 번째 일요일 0시에 시작하여 이듬해 2월의 세 번째 일요일 0시에 해제한다.

폐지된 나라[편집]

이집트[편집]

이집트는 4월의 마지막 금요일 낮 12시에 시작되어 9월의 마지막 금요일 낮 12시에 해제하였다. 그러나 2011년 4월부터 일광 절약 시간제를 폐지하기로 합의했다.[5] 따라서 이 이후부터 대한민국과 이집트의 시차는 7시간으로 고정된다.

러시아[편집]

러시아는 UTC로 3월의 마지막 일요일 오전 2시에 시작하여 10월의 마지막 일요일 오전 3시에 해제한다. 하지만 러시아 역시 2011년 3월에 일광 절약 시간제를 적용한 후 이를 해제하지 않기로 합의했다.[6] 따라서 대한민국과 러시아 모스크바의 시차는 6시간으로 고정되었다. 같은 논의가 벨라루스에서도 이루어져 같은 해에 폐지되었다.

이라크[편집]

이라크는 4월의 첫 번째 토요일 오전 3시에 시작하여 10월의 첫 번째 일요일 오전 4시에 해제한다. 그러나 이 역시도 2007년 이후로 폐지되었다.

이외에도 많은 나라들이 21세기 이후로 폐지하여 2019년 기준으로 북미, 중동 일부 국가와 남반구 일부 지역에서만 실시되고 있다.

유럽[편집]

중부 유럽지역은 3월 마지막 일요일 오전 1시(GMT 기준)에 시작하여 10월 마지막 일요일 오전 2시에 해제된다. 그렇게 되면 대한민국과 영국,포르투갈,아일랜드의 시간차는 8시간으로, 독일,프랑스,이탈리아,스페인 등 대륙 주요국은 7시간으로 줄어든다. 핀란드,불가리아,그리스 등과는 시차가 6시간이 된다.

1996년에 유럽 연합 법률은 모든 유럽 연합 국가들이 써머 타임을 적용하도록 강제하였다. 그러나 2018년 9월에 유럽 연합에서 2019년 10월부터 계절성 시간 변화를 폐지하기로 하였다. 2019년 4월까지 여름 시간이나 겨울 시간 중에 어느 시간대를 앞으로 영구적으로 쓸 지 각 회원국들이 개별적으로 결정하도록 하였다.[7]

대한민국[편집]

대한민국에서는 1948년~1951년, 1955년~1960년, 1987년~1988년에 일광 절약 시간제가 실시되었다. 조선민주주의인민공화국에서는 일광 절약 시간제가 시행된 적이 없다.

대한민국에서는 1955년~1960년의 기간에 표준시의 기준 자오선이 동경 127° 30'으로 현재보다 30분 늦은 시간대를 썼기 때문에, 서머 타임 실시 중에는 현재보다 30분을 앞당긴 셈이었다. 1987년과 1988년의 서머 타임은 서울 올림픽 TV중계를 위해 실시한 제도로, 시민들의 생활 리듬을 깨고 혼란만 야기시킨다는 비난 여론이 빗발쳐[8][9] 올림픽이 끝난 후에는 시행되지 않았다.

2009년 이명박 대통령 직속 녹색성장위원회에서 일광절약시간제 도입을 추진하기도 했으나,[10][11] 대한민국은 동경 135° 기준인 UTC+09:00를 쓰기 때문에 이미 연중 30분 가량 일광절약시간제가 시행되는 효과가 있다는 반론과 함께, 생활의 불편과 혼란만 야기한다는 반대 여론이 많아 시행되지 않았다.

대한민국의 일광 절약 시간제 실시 시기

1948.06.01. 00:00 ~ 1948.09.13. 00:00

1949.04.03. 00:00 ~ 1949.09.11. 00:00

1950.04.01. 00:00 ~ 1950.09.10. 00:00

1951.05.06. 00:00 ~ 1951.09.09. 00:00

1955.05.05. 00:00 ~ 1955.09.09. 00:00

1956.05.20. 00:00 ~ 1956.09.30. 00:00

1957.05.05. 00:00 ~ 1957.09.22. 00:00

1958.05.04. 00:00 ~ 1958.09.21. 00:00

1959.05.03. 00:00 ~ 1959.09.20. 00:00

1960.05.01. 00:00 ~ 1960.09.18. 00:00

1987.05.10. 02:00 ~ 1987.10.11. 03:00

1988.05.08. 02:00 ~ 1988.10.09. 03:00

에너지 사용에 대한 영향[편집]

일광절약제는 냉난방수요를 유발해 전기사용량을 증가시킨다. 학술지 "경제와 통계 논평(The review of economics and statistics)” 2011년 93권 4호에 실린 논문 "일광절약제도는 에너지를 절약할까? 인디애나의 자연적 실험을 통한 근거(Does daylight saving time save energy? Evidence from a natural experiment in Indiana)”에 따르면, 매년 4~10월에 전기사용량이 더 많다. 전반적으로 0.98%를 더 사용한다. 일광절약제가 실시되는 기간 냉방으로 인한 전기 수요가 증가하기 때문이다.[12][13]

인간행동에 대한 영향[편집]

학술지 수면의학평론(Sleep medicine reviews)에 실린 논문 "일광절약제가 수면과 인간행동에 미치는 영향(The impact of daylight saving time on sleep and related behaviors)"은 일광절약제 시행의 영향을 과학적으로 탐구한 연구논문 약 60편을 분석해, 일광절약제가 수면, 교통사고, 사망, 건강, 인지능력, 및 업무생산성 등에 미치는 영향을 한 종합적으로 제시했다.[14]

수면[편집]

  • 시간을 당기는 봄철에는 DST시행후 한 달 간 수면시간이 40분 정도 감소하나, 원상복귀하는 가을에는 수면시간 변화 없음.

  • 아침형은 봄철 시간조정에 적응을 잘하는 편이나, 저녁형은 수면의 질이 크게 나빠짐.

  • 새롭게 설정된 기상 시간에 적응하는 기간은 5일 정도 소요.

교통사고[편집]

  • 봄철 시간조정 이후 약 2주 동안 대체로 교통사고 발생 7-10% 증가. 다만, 스웨덴 핀란드 등 북구에 위치한 지역에서 실시한 연구에서는 봄철에도 교통사고 증가가 관측되지 않았음. 해가 늦게 뜨는 북구지역은 봄철 시간조정으로 출근시간을 한시간 당겨도 도로의 상황변화가 크지 않았기 때문인 것으로 추론 가능.

  • 가을철 시간조정 이후에는 교통사고 발생 변화 없음.

사망[편집]

  • 봄철 시간조정 이후 일주일간 사망률 6.5% 증가. 가을철 시간조정이후에는 사망률에 변화 없음.

건강[편집]

  • 급성심근경색과 뇌졸증 발생 증가

  • 자살율에 대해서는 연구결과가 일치하지 않음. 일광절약제 시행과 자살시도와의 상관성을 찾은 연구도 있지만, 상관성을 찾지 못한 연구도 있음.

인지능력[편집]

  • 인디애나주에서는 2006년 이전에는 21%의 지역에서 일광절약시간제를 시행했으나, 2006년 주내의 모든 지역에서 실시하도록 강제했음. 따라서 인디애나 주는 자연스럽게 비슷한 지역의 비슷한 사람을 대상으로 일광절약시간제의 영향을 비교할 수 있는 상황이 조성. 인디애나주 350개 고등학교의 SAT(Scholastic Assessment Test)점수 10년치를 비교한 결과, 일광절약시간제를 시행한 지역 고등학교의 성적이 유의미하게 낮았음. 이는 수면리듬의 혼란이 인지능력을 손상시킬 수 있다는 견해를 뒷받침[15].

업무생산성[편집]

  • 봄철 시간조정 이후 근무시간에 딴짓하는 시간 증가. 봄철 시간조정 직후 월요일의 인터넷 검색기록을 시간조정 직전의 월요일의 검색기록과 비교했을 때, 일과 관련이 없는 오락과 관련된 내용 검색이 유의미하게 많았음. 논문 저자는 이를 수면시간 감소에 따른 자아조절 능력의 상실로 해석[16].

기타 비판[편집]

이외에도 일광절약시간제는 다음과 같은 이유로 비판받고 있다.

  1. 전 세계의 컴퓨터 시간을 바꾸는 데 엄청난 시간을 소모하고 혼란을 일으킨다. 이는 실시하고 있지 않은 지역에서도 마찬가지로 발생하며, 전 세계 수많은 컴퓨터의 작동 시간이 이에 소요되고 있으며, 국제 간 연락에도 영향을 미치고 있다.

  2. 여러 시간대(특히 일광절약시간제를 쓰지 않는 시간대와 쓰는 시간대)를 오가는 사람들에게 혼란을 일으킬 수 있다.

  3. 해마다 두 차례씩 시간을 맞추어야 하니 번거롭다.

  4. 일광 절약 시간제는 전 세계적으로 쓰이지 않는다.

  5. 한 시간이 중복되는 경우가 생긴다.

  6. 학생과 직장인은 일광절약시간제의 시작과 끝에는 해가 뜨지도 않았는데 등교/출근해야 하는 경우가 생긴다.

  7. 농부들은 시간에 관계 없이 해가 뜨면 일어나야 한다. 그리고 젖소의 젖이 나오는 때는 시계가 가리키는 시간에 관계없이 일정하다.

Daylight saving time (DST), also daylight savings time or daylight time (the United States and Canada) and summer time (United Kingdom, European Union, and others), is the practice of advancing clocks during warmer months so that darkness falls at a later clock time. The typical implementation of DST is to set clocks forward by one hour in the spring ("spring forward") and set clocks back by one hour in autumn ("fall back", from the North American English word "fall" for autumn) to return to standard time. As a result, there is one 23-hour day in late winter or early spring and one 25-hour day in the autumn.

George Hudson proposed the idea of daylight saving in 1895. The German Empire and Austria-Hungary organized the first nationwide implementation starting on April 30, 1916. Many countries have used it at various times since then, particularly since the 1970s energy crisis. DST is generally not observed near the equator, where sunrise and sunset times do not vary enough to justify it. Some countries observe it only in some regions; for example, parts of Australia observe it, while other parts do not, and the United States observes it, except Arizona and Hawaii, which do not. Only a minority of the world's population uses DST; Asia and Africa generally do not observe it.

DST clock shifts sometimes complicate timekeeping and can disrupt travel, billing, record keeping, medical devices, heavy equipment, and sleep patterns. Computer software generally adjusts clocks automatically.

Contents

Rationale[edit]

 

An ancient water clock that lets hour lengths vary with season.

Industrialized societies usually follow a clock-based schedule for daily activities that do not change throughout the course of the year. The time of day that individuals begin and end work or school, and the coordination of mass transit, for example, usually remain constant year-round. In contrast, an agrarian society's daily routines for work and personal conduct are more likely governed by the length of daylight hours[1][2] and by solar time, which change seasonally because of the Earth's axial tilt. North and south of the tropics daylight lasts longer in summer and shorter in winter, with the effect becoming greater the further one moves away from the tropics.

By synchronously resetting all clocks in a region to one hour ahead of standard time, individuals who follow such a year-round schedule will wake an hour earlier than they would have otherwise; they will begin and complete daily work routines an hour earlier, and they will have available to them an extra hour of daylight after their workday activities.[3][4] However, they will have one less hour of daylight at the start of each day, making the policy less practical during winter.[5][6]

While the times of sunrise and sunset change at roughly equal rates as the seasons change, proponents of daylight saving time argue that most people prefer a greater increase in daylight hours after the typical "nine to five" workday.[7][8] Supporters have also argued that DST decreases energy consumption by reducing the need for lighting and heating, but the actual effect on overall energy use is heavily disputed.

The manipulation of time at higher latitudes (for example Iceland, Nunavut, Scandinavia or Alaska) has little impact on daily life, because the length of day and night changes more extremely throughout the seasons (in comparison to other latitudes), and thus sunrise and sunset times are significantly out of phase with standard working hours regardless of manipulations of the clock.[9] DST is also of little use for locations near the equator, because these regions see only a small variation in daylight in the course of the year.[10] The effect also varies according to how far east or west the location is within its time zone, with locations farther east inside the time zone benefiting more from DST than locations farther west in the same time zone.[11]

History[edit]

Ancient civilizations adjusted daily schedules to the sun more flexibly than DST does, often dividing daylight into 12 hours regardless of daytime, so that each daylight hour became progressively longer during spring and shorter during autumn.[12] For example, the Romans kept time with water clocks that had different scales for different months of the year; at Rome's latitude, the third hour from sunrise (hora tertia) started at 09:02 solar time and lasted 44 minutes at the winter solstice, but at the summer solstice it started at 06:58 and lasted 75 minutes.[13] From the 14th century onwards, equal-length civil hours supplanted unequal ones, so civil time no longer varied by season. Unequal hours are still used in a few traditional settings, such as some monasteries of Mount Athos[14] and all Jewish ceremonies.[15]

 

George Hudson invented modern DST, proposing it first in 1895.

Benjamin Franklin published the proverb "early to bed and early to rise makes a man healthy, wealthy, and wise",[16][17] and published a letter in the Journal de Paris during his time as an American envoy to France (1776–1785) suggesting that Parisians economize on candles by rising earlier to use morning sunlight.[18] This 1784 satire proposed taxing window shutters, rationing candles, and waking the public by ringing church bells and firing cannons at sunrise.[19] Despite common misconception, Franklin did not actually propose DST; 18th-century Europe did not even keep precise schedules. However, this changed as rail transport and communication networks required a standardization of time unknown in Franklin's day.[20]

In 1810, the Spanish National Assembly Cortes of Cádiz issued a regulation that moved certain meeting times forward by one hour from May 1 to September 30 in recognition of seasonal changes, but it did not actually change the clocks. It also acknowledged that private businesses were in the practice of changing their opening hours to suit daylight conditions, but they did so of their own volition.[21][22]

New Zealand entomologist George Hudson first proposed modern DST. His shift-work job gave him leisure time to collect insects and led him to value after-hours daylight.[23] In 1895, he presented a paper to the Wellington Philosophical Society proposing a two-hour daylight-saving shift,[3] and considerable interest was expressed in Christchurch; he followed up with an 1898 paper.[24] Many publications credit the DST proposal to prominent English builder and outdoorsman William Willett,[25] who independently conceived DST in 1905 during a pre-breakfast ride when he observed how many Londoners slept through a large part of a summer day.[8] Willett also was an avid golfer who disliked cutting short his round at dusk.[26] His solution was to advance the clock during the summer months, and he published the proposal two years later.[27] Liberal Party member of parliament Robert Pearce took up the proposal, introducing the first Daylight Saving Bill to the House of Commons on February 12, 1908.[28] A select committee was set up to examine the issue, but Pearce's bill did not become law and several other bills failed in the following years.[29] Willett lobbied for the proposal in the UK until his death in 1915.

Port Arthur, Ontario, Canada was the first city in the world to enact DST, on July 1, 1908.[30][31] This was followed by Orillia, Ontario, introduced by William Sword Frost while mayor from 1911 to 1912.[32] The first states to adopt DST (German: Sommerzeit) nationally were those of the German Empire and its World War I ally Austria-Hungary commencing April 30, 1916, as a way to conserve coal during wartime. Britain, most of its allies, and many European neutrals soon followed. Russia and a few other countries waited until the next year, and the United States adopted daylight saving in 1918. Most jurisdictions abandoned DST in the years after the war ended in 1918, with exceptions including Canada, the UK, France, Ireland, and the United States.[33] It became common during World War II, and was widely adopted in America and Europe from the 1970s as a result of the 1970s energy crisis. Since then, the world has seen many enactments, adjustments, and repeals.[34]

Procedure[edit]

See also: Daylight saving time by country

When DST observation begins, clocks are advanced by one hour (as if to skip one hour) during the very early morning.

When DST observation ends and standard time observation resumes, clocks are turned back one hour (as if to repeat one hour) during the very early morning. Specific times of the clock change vary by jurisdiction.

The relevant authorities usually schedule clock changes to occur at (or soon after) midnight, and on a weekend, in order to lessen disruption to weekday schedules.[35] A one-hour change is customary, but twenty-minute and two-hour changes have been used in the past. In all countries that observe daylight saving time seasonally (i.e. during summer and not winter), the clock is advanced from standard time to daylight saving time in the spring, and they are turned back from daylight saving time to standard time in the autumn. The practice, therefore, reduces the number of civil hours in the day of the springtime change, and it increases the number of civil hours in the day of the autumnal change. For a midnight change in spring, a digital display of local time would appear to jump from 23:59:59.9 to 01:00:00.0. For the same clock in autumn, the local time would appear to repeat the hour preceding midnight, i.e. it would jump from 23:59:59.9 to 23:00:00.0.

In most countries that observe seasonal daylight saving time, the clock observed in winter is legally named "standard time",[36] in accordance with the standardization of time zones to agree with the local mean time near the center of each region.[37] An exception exists in Ireland, where its winter clock has the same offset (UTC±00:00) and legal name as that in Britain (Greenwich Mean Time)—but while its summer clock also has the same offset as Britain's (UTC+01:00), its legal name is Irish Standard Time[38][39] as opposed to British Summer Time.[40]

While most countries that change clocks for daylight saving time observe standard time in winter and DST in summer, Morocco observes (since 2019) daylight saving time every month but Ramadan. During the holy month (the date of which is determined by the lunar calendar and thus moves annually with regard to the Gregorian calendar), the country's civil clocks observe Western European Time (UTC+00:00, which geographically overlaps most of the nation). At the close of this month, its clocks are turned forward to Western European Summer Time (UTC+01:00), where they remain until the return of the holy month the following year.[41][42][43]

The time at which to change clocks differs across jurisdictions. Members of the European Union conduct a coordinated change, changing all zones at the same instant, at 01:00 Coordinated Universal Time (UTC), which means that it changes at 02:00 Central European Time (CET), equivalent to 03:00 Eastern European Time (EET). As a result, the time differences across European time zones remain constant.[44][45] North America coordination of the clock change differs, in that each jurisdiction change at 02:00 local time, which temporarily creates unusual differences in offsets. For example, Mountain Time is, for one hour in the autumn, zero hours ahead of Pacific Time instead of the usual one hour ahead, and, for one hour in the spring, it is two hours ahead of Pacific Time instead of one.

The dates on which clocks change vary with location and year; consequently, the time differences between regions also vary throughout the year. For example, Central European Time is usually six hours ahead of North American Eastern Time, except for a few weeks in March and October/November, while the United Kingdom and mainland Chile could be five hours apart during the northern summer, three hours during the southern summer, and four hours for a few weeks per year. Since 1996, European Summer Time has been observed from the last Sunday in March to the last Sunday in October; previously the rules were not uniform across the European Union.[45] Starting in 2007, most of the United States and Canada observed DST from the second Sunday in March to the first Sunday in November, almost two-thirds of the year.[46] Moreover, the beginning and ending dates are roughly reversed between the northern and southern hemispheres because spring and autumn are displaced six months. For example, mainland Chile observes DST from the second Saturday in October to the second Saturday in March, with transitions at 24:00 local time.[47] In some countries time is governed by regional jurisdictions within the country such that some jurisdictions change and others do not; this is currently the case in Australia, Canada, Mexico, and the United States (formerly in Brazil, etc.).[48][49]

From year to year, the dates on which to change clock may also move for political or social reasons. The Uniform Time Act of 1966 formalized the United States' period of daylight saving time observation as lasting six months (it was previously declared locally); this period was extended to seven months in 1986, and then to eight months in 2005.[50][51][52] The 2005 extension was motivated in part by lobbyists from the candy industry, seeking to increase profits by including Halloween (October 31) within the daylight saving time period.[53] In recent history, Australian state jurisdictions not only changed at different local times but sometimes on different dates. For example, in 2008 most states there that observed daylight saving time changed clocks forward on October 5, but Western Australia changed on October 26.[54]

Politics, religion and sport[edit]

The concept of daylight saving has caused controversy since its early proposals.[55] Winston Churchill argued that it enlarges "the opportunities for the pursuit of health and happiness among the millions of people who live in this country"[56] and pundits have dubbed it "Daylight Slaving Time".[57] Retailing, sports, and tourism interests have historically favored daylight saving, while agricultural and evening-entertainment interests have opposed it; energy crises and war prompted its initial adoption.[58]

The fate of Willett's 1907 proposal illustrates several political issues. It attracted many supporters, including Arthur Balfour, Churchill, David Lloyd George, Ramsay MacDonald, King Edward VII (who used half-hour DST or "Sandringham time" at Sandringham, the managing director of Harrods, and the manager of the[which?] National Bank. However, the opposition proved stronger, including Prime Minister H. H. Asquith, William Christie (the Astronomer Royal), George Darwin, Napier Shaw (director of the Meteorological Office), many agricultural organizations, and theatre-owners. After many hearings, a parliamentary committee vote narrowly rejected the proposal in 1909. Willett's allies introduced similar bills every year from 1911 through 1914, to no avail.[59] People in the U.S. demonstrated even more skepticim; Andrew Peters introduced a DST bill to the House of Representatives in May 1909, but it soon died in committee.[60]

 

Retailers generally favor DST; United Cigar Stores hailed a 1918 DST bill.

Germany together with its allies led the way in introducing DST (German: Sommerzeit) during World War I on April 30, 1916, aiming to alleviate hardships due to wartime coal-shortages and from air-raid blackouts. The political equation changed in other countries; the United Kingdom used DST first on May 21, 1916.[61] U.S. retailing and manufacturing interests - led by Pittsburgh industrialist Robert Garland - soon began lobbying for DST, but railroads opposed the idea. The U.S.'s 1917 entry into the war overcame objections, and DST started in 1918.[62]

The war's end swung the pendulum back. Farmers continued to dislike DST, and many countries repealed it after the war - like Germany itself, which dropped DST from 1919 to 1939 and from 1950 to 1979.[63] Britain proved an exception; it retained DST nationwide but adjusted transition dates over the years for several reasons, including special rules during the 1920s and 1930s to avoid clock shifts on Easter mornings. As of 2009 summer time began annually on the last Sunday in March under a European Community directive, which may be Easter Sunday (as in 2016).[45] The U.S. dithered more; Congress repealed DST after 1919. President Woodrow Wilson - an avid golfer like Willett - vetoed the repeal twice, but his second veto was overridden.[64] Only a few U.S. cities retained DST locally,[65] including New York (so that its financial exchanges could maintain an hour of arbitrage trading with London), and Chicago and Cleveland (to keep pace with New York).[66] Wilson's successor as President, Warren G. Harding, opposed DST as a "deception", reasoning that people should instead get up and go to work earlier in the summer. He ordered District of Columbia federal employees to start work at 8 am rather than 9 am during the summer of 1922. Some businesses followed suit, though many others did not; the experiment was not repeated.[4]

Since Germany's adoption of DST in 1916, the world has seen many enactments, adjustments, and repeals of DST, with similar politics involved.[67] The history of time in the United States features DST during both world wars, but no standardization of peacetime DST until 1966.[68][69] St. Paul and Minneapolis, Minnesota, kept different times for two weeks in May 1965: the capital city decided to switch to daylight saving time, while Minneapolis opted to follow the later date set by state law.[70][71] In the mid-1980s, Clorox and 7-Eleven provided the primary funding for the Daylight Saving Time Coalition behind the 1987 extension to U.S. DST. Both senators from Idaho, Larry Craig and Mike Crapo, voted for it based on the premise that fast-food restaurants sell more French fries (made from Idaho potatoes) during DST.[72]

A referendum on the introduction of daylight saving took place in Queensland, Australia, in 1992, after a three-year trial of daylight saving. It was defeated with a 54.5% "no" vote, with regional and rural areas strongly opposed, and those in the metropolitan southeast in favor.[73] In 2005 the Sporting Goods Manufacturers Association and the National Association of Convenience Stores successfully lobbied for the 2007 extension to U.S. DST.[74] In December 2008 the Daylight Saving for South East Queensland (DS4SEQ) political party was officially registered in Queensland, advocating the implementation of a dual-time-zone arrangement for daylight saving in South East Queensland, while the rest of the state maintained standard time.[75] DS4SEQ contested the March 2009 Queensland state election with 32 candidates and received one percent of the statewide primary vote, equating to around 2.5% across the 32 electorates contested.[76] After a three-year trial, more than 55% of Western Australians voted against DST in 2009, with rural areas strongly opposed.[77] Queensland Independent member Peter Wellington introduced the Daylight Saving for South East Queensland Referendum Bill 2010 into the Queensland parliament on April 14, 2010, after being approached by the DS4SEQ political party, calling for a referendum at the next state election on the introduction of daylight saving into South East Queensland under a dual-time-zone arrangement.[78] The Queensland parliament rejected Wellington's bill on June 15, 2011.[79]

In the UK, the Royal Society for the Prevention of Accidents supports a proposal to observe SDST's additional hour year-round, but that is opposed by some industries, by some postal workers and farmers, and particularly by those living in the northern regions of the UK.[2] In some Muslim countries, DST is temporarily abandoned during Ramadan (the month when no food should be eaten between sunrise and sunset), since the DST would delay the evening dinner.[citation needed] Iran maintains DST during Ramadan,[80] but most Muslim countries do not use DST, partially for this reason.[81]

Russia declared in 2011 that it would stay in DST all year long; Belarus followed with a similar declaration.[82] (The Soviet Union had operated under permanent "summer time" from 1930 to at least 1982.) Russia's plan generated widespread complaints due to the dark of winter-time mornings, and thus was abandoned in 2014.[83] The country changed its clocks to standard time on October 26, 2014, intending to stay there permanently.[84]

Impacts[edit]

Main article: Analysis of daylight saving time

 

William Willett independently proposed DST in 1907 and advocated it tirelessly.[85]

Proponents of DST generally argue that it saves energy, promotes outdoor leisure activity in the evening (in summer), and is therefore good for physical and psychological health, reduces traffic accidents, reduces crime[citation needed] or is good for business.[86]

A 2017 meta-analysis of 44 studies found that DST leads to electricity savings of 0.3% during the days when DST applies.[87][88] Several studies have suggested that DST increases motor fuel consumption,[89] but a 2008 United States Department of Energy report found no significant increase in motor gasoline consumption due to the 2007 United States extension of DST.[90] An early goal of DST was to reduce evening usage of incandescent lighting, once a primary use of electricity.[91] Although energy conservation remains an important goal,[92] energy usage patterns have greatly changed since then. Electricity use is greatly affected by geography, climate, and economics, so the results of a study conducted in one place may not be relevant to another country or climate.[89]

Later sunset times from DST are thought to affect behavior, for example increasing participation in after-school sports programs or outdoor afternoon sports such as golf, and attendance at professional sporting events.[93] Advocates of daylight saving time argue that having more hours of daylight between the end of a typical workday and evening induces people to consume other goods and services.[94][86][95]

Many farmers oppose DST, particularly dairy farmers as the milking patterns of their cows do not change with the time.[96][97][98] and others whose hours are set by the sun.[99] Young children often have difficulty getting enough sleep at night when the evenings are bright.[96] DST also hurts prime-time television broadcast ratings,[100][96] drive-ins and other theaters.[101]

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,[102] Others have asserted that the observed results depend on methodology[103] and disputed the findings,[104] though the original authors have refuted points raised by disputers.[105]

A correlation between clock shifts and traffic accidents has been observed in North America and the UK but not in Finland or Sweden. Four reports have found that this effect is smaller than the overall reduction in traffic fatalities.[106][107][108][109] DST likely reduces some kinds of crime, such as robbery and sexual assault, as fewer potential victims are outdoors after dusk.[110][111] Artificial outdoor lighting has a marginal and sometimes even contradictory influence on crime and fear of crime.[112] A 2017 study in the American Economic Journal: Applied Economics estimated that "the transition into DST caused over 30 deaths at a social cost of $275 million annually," primarily by increasing sleep deprivation.[113]

Opponents argue that DST disrupts human circadian rhythms (negatively impacting human health in the process),[114][115] that it increases fatal traffic collisions,[116] that the actual energy savings are inconclusive,[96] and that DST increases health risks such as heart attack.[96] Year-round standard time (not year-round DST) is proposed to be the preferred option for public health and safety.[117][118][119][120][121] Clock shifts were found to increase the risk of heart attack by 10 percent,[96] and to disrupt sleep and reduce its efficiency.[122] Effects on seasonal adaptation of the circadian rhythm can be severe and last for weeks.[123]

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.[124] People who work across time zone boundaries need to keep track of multiple DST rules, as not all locations observe DST or observe it the same way. The length of the 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.[125] 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.[126]

Some clock-shift problems could be avoided by adjusting clocks continuously[127] or at least more gradually[128]—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. For example, when reading a sundial, one must compensate for it along with time zone and natural discrepancies.[129] Also, sun-exposure guidelines such as avoiding the sun within two hours of noon become less accurate when DST is in effect.[130]

Terminology[edit]

As explained by Richard Meade in the English Journal of the (American) National Council of Teachers of English, the form daylight savings time (with an "s") was already in 1978 much more common than the older form daylight saving time in American English ("the change has been virtually accomplished"). Nevertheless, even dictionaries such as Merriam-Webster's, American Heritage, and Oxford, which describe actual usage instead of prescribing outdated usage (and therefore also list the newer form), still list the older form first. This is because the older form is still very common in print and preferred by many editors. ("Although daylight saving time is considered correct, daylight savings time (with an "s") is commonly used.")[131] The first two words are sometimes hyphenated (daylight-saving(s) time). Merriam-Webster's also lists the forms daylight saving (without "time"), daylight savings (without "time"), and daylight time.[132] The Oxford Dictionary of American Usage and Style explains the development and current situation as follows: "Although the singular form daylight saving time is the original one, dating from the early 20th century—and is preferred by some usage critics—the plural form is now extremely common in AmE. [...] The rise of daylight savings time appears to have resulted from the avoidance of a miscue: when saving is used, readers might puzzle momentarily over whether saving is a gerund (the saving of daylight) or a participle (the time for saving). [...] Using savings as the adjective—as in savings account or savings bond—makes perfect sense. More than that, it ought to be accepted as the better form."[133]

In Britain, Willett's 1907 proposal[27] used the term daylight saving, but by 1911 the term summer time replaced daylight saving time in draft legislation.[85] The same or similar expressions are used in many other languages: Sommerzeit in German, zomertijd in Dutch, kesäaika in Finnish, horario de verano or hora de verano in Spanish, and heure d'été in French.[61]

The name of local time typically changes when DST is observed. American English replaces standard with daylight: for example, Pacific Standard Time (PST) becomes Pacific Daylight Time (PDT). In the United Kingdom, the standard term for UK time when advanced by one hour is British Summer Time (BST), and British English typically inserts summer into other time zone names, e.g. Central European Time (CET) becomes Central European Summer Time (CEST).

The North American English mnemonic "spring forward, fall back" (also "spring ahead ...", "spring up ...", and "... fall behind") helps people remember in which direction to shift the clocks.[55]

Computing[edit]

 

A 2001 US public service advertisement reminded people to adjust clocks.

Changes to DST rules cause problems in existing computer installations. For example, the 2007 change to DST rules in North America required that many computer systems be upgraded, with the greatest impact on e-mail and calendar programs. The upgrades required a significant effort by corporate information technologists.[134]

Some applications standardize on UTC to avoid problems with clock shifts and time zone differences.[135] Likewise, most modern operating systems internally handle and store all times as UTC and only convert to local time for display.[136][137]

However, even if UTC is used internally, the systems still require external leap second updates and time zone information to correctly calculate local time as needed. Many systems in use today base their date/time calculations from data derived from the tz database also known as zoneinfo.

IANA time zone database[edit]

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 operating systems, Java, and the Oracle RDBMS;[138] HP's "tztab" database is similar but incompatible.[139] When temporal authorities change DST rules, zoneinfo updates are installed as part of ordinary system maintenance. In Unix-like systems the TZ environment variable specifies the location name, as in TZ=':America/New_York'. In many of those systems there is also a system-wide setting that is applied if the TZ environment variable is not set: this setting is controlled by the contents of the /etc/localtime file, which is usually a symbolic link or hard link to one of the zoneinfo files. Internal time is stored in time-zone-independent Unix 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, 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 the eastern United States starting in 2007. Such a TZ value must be changed whenever DST rules change, and the new value applies to all years, mishandling some older timestamps.[140]

Permanent daylight saving time[edit]

See also: Permanent time observation in the United States, Decree time in Russia, Summer time in Europe § Future, Daylight saving time in Asia § Asian countries not using DST, and Daylight saving time in Brazil

 

The William Willett Memorial Sundial in Petts Wood, south London, is always on DST.

A move to permanent daylight saving time (staying on summer hours all year with no time shifts) is sometimes advocated and is currently implemented in some jurisdictions such as Argentina, Belarus,[141] Saskatchewan, Yukon, Iceland, Kyrgyzstan, Magallanes and Chilean Antarctica Region, Malaysia, Morocco,[42] Namibia, Singapore, Turkey, Turkmenistan and Uzbekistan. Advocates cite the same advantages as normal DST without the problems associated with the twice yearly time shifts. However, many remain unconvinced of the benefits, citing the same problems and the relatively late sunrises, particularly in winter, that year-round DST entails.[6]

Russia switched to permanent DST from 2011 to 2014, but the move proved unpopular because of the late sunrises in winter, so in 2014, Russia switched permanently back to standard time.[142] The United Kingdom and Ireland also experimented with year-round summer time between 1968 and 1971, and put clocks forward by an extra hour during World War II.[143]

In the United States, the Florida, Washington, California, and Oregon legislatures have all passed bills to enact permanent DST, but the bills require Congressional approval in order to take effect. Maine, Massachusetts, New Hampshire, and Rhode Island have also introduced proposals or commissions to that effect.[144][145][146][147][148] Although 26 states have considered making DST permanent, unless Congress changes federal law, states cannot implement permanent DST—states can only opt out of DST, not standard time.[149]

In September 2018, the European Commission proposed to end seasonal clock changes as of 2019.[150] Member states would have the option of observing either daylight saving time all year round or standard time all year round. In March 2019, the European Parliament approved the commission's proposal, while deferring implementation from 2019 until 2021.[151] As of October 2020, the decision has not been confirmed by the Council of the European Union.[152] The council has asked the commission to produce a detailed impact assessment, but the Commission considers that the onus is on the Member States to find a common position in Council.[153] As a result, progress on the issue is effectively blocked.[154]

Experts in circadian rhythms and sleep caution against permanent daylight saving time, recommending year-round standard time as the preferred option for public health and safety.[117][118][119][120]

Perceived problems with permanent DST[edit]

Since daylight saving time creates the illusion of the sun rising and setting one hour later on the clock, but does not add any additional daylight, the already later sunrise times under standard time are pushed an hour later on the clock with daylight saving time. Late sunrise times can become unpopular in the winter months which essentially forces workers and schoolchildren to begin the day in darkness. In 1974 following the enactment of the Emergency Daylight Saving Time Act in the United States, there were complaints of children going to school in the dark and working people commuting and starting their work day in pitch darkness during the winter months. The complaints led to the repeal of the act in October 1974 when standard time was restored until February 23, 1975. In 1976, the United States returned to the schedule set under the Uniform Time Act of 1966. In 1971, year-round daylight time in the United Kingdom was abandoned after a 3-year experiment because of complaints about winter sunrise times. The same complaints also led to Russia abandoning DST and instituting standard time year round in 2014.[142]

By country and region[edit]

Main article: Daylight saving time by country

See also[edit]

References[edit]

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  123. ^ DST and circadian rhythm:

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  125. ^ Paul McDougall (March 1, 2007). "PG&E says patching meters for an early daylight-saving time will cost $38 million". InformationWeek.

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  127. ^ Jesse Ruderman (November 1, 2006). "Continuous daylight saving time".

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  130. ^ Leith Holloway (1992). "Atmospheric sun protection factor on clear days: its observed dependence on solar zenith angle and its relevance to the shadow guideline for sun protection". Photochemistry and Photobiology. 56 (2): 229–234. doi:10.1111/j.1751-1097.1992.tb02151.x. PMID 1502267.

  131. ^ Seize the Daylight (2005), p. xv.

  132. ^ Daylight saving time and its variants:

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  143. ^ Hollingshead, Iain (June 2006). "Whatever happened to Double Summer Time?". The Guardian. London.

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  148. ^ Butler, Grant (October 29, 2019). "When does daylight saving time end? It's time for that annual 'fall back' ritual". The Oregonian. Retrieved November 3, 2019.

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  150. ^ "Press corner". European Commission - European Commission. September 12, 2018. Retrieved October 23, 2020.

  151. ^ "European parliament votes to scrap daylight saving time from 2021". The Guardian (US ed.). London. March 26, 2019. Retrieved July 9, 2019.

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  153. ^ Posaner, Joshua; Cokelaere, Hanne (October 24, 2020). "Stopping the clock on seasonal time changes? Not anytime soon". Politico.

  154. ^ Lawson, Patrick (November 18, 2020). "The plan to abolish the time change is "completely blocked" at European level, says specialist in European issues". Geads News.

Sources[edit]

Further reading[edit]

  • Ian R. Bartky (2007). One Time Fits All: The Campaigns for Global Uniformity. Stanford University Press. ISBN 978-0-8047-5642-6.

External links[edit]

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