Important Changes to Daylight Savings Time

Origin

Saving daylight was first mentioned in 1784 by Benjamin Franklin in a satirical essay[1] urging Parisians to get up earlier in order to use sunlight, thus saving wax by not burning candles at night, in the spirit of his proverb "Early to bed and early to rise / Makes a man healthy, wealthy, and wise."[2] Franklin did not mention Daylight Saving Time—he did not propose that clock time be changed.

DST was first seriously proposed in 1907 by William Willett,[3] but he was unable to get the British government to adopt it, despite considerable lobbying.

DST was first put into practice by a national government in Germany during the First World War, between April 30, 1916 and October 1, 1916. Shortly afterward, the United Kingdom followed suit, first adopting it between May 21 and October 1, 1916. On June 17, 1917, Newfoundland became the first North American jurisdiction to adopt DST with the passing of the Daylight Saving Act of 1917. On March 19, 1918, the U.S. Congress formally established several time zones, which had been in use by railroads and most cities since 1883; at the same time it established DST from the last Sunday in March to the last Sunday in October. The law, however, proved so unpopular, mostly because it obliged people to rise and go to bed earlier than had become customary since the advent of electricity, that it was repealed after 1919, when Congress overrode President Woodrow Wilson's veto of the repeal.

Observation of DST

In a typical case where a one-hour shift occurs at 02:00 local time, in spring the clock jumps forward from 01:59:59.999… to 03:00 and that day is 23 hours long, whereas in autumn the clock jumps backward from 01:59:59.999… to 01:00, repeating that hour, and the day is 25 hours long. A one hour clock shift is customary, but Lord Howe Island uses a half-hour shift, and twenty-minute and two-hour shifts have occurred in the past.

Clock shifts typically occur near a weekend midnight to lessen disruption to weekday schedules. In some jurisdictions, such as California, bars are required to close at 02:00, which is when the clock shift occurs, leaving bars open for an extra hour once a year—one of the few direct commercial effects. Hospitals and other 24/7 operations change their clocks but remain open.

Start and end dates and times vary with location and year. Starting in 2007, most of the United States and Canada observe DST from the second Sunday in March to the first Sunday in November, with transitions typically at 02:00 local time. The 2007 U.S. change was part of the Energy Policy Act of 2005; previously, from 1987 through 2006, the start and end dates were the first Sunday in April and the last Sunday in October, and Congress retains the right to go back to the previous dates once an energy consumption study is done. Since 1996 the European Union has observed DST from the last Sunday in March to the last Sunday in October, with transitions at 01:00 UTC.

Beginning and ending dates are switched in the southern hemisphere. For example, mainland Chile observes DST from the second Saturday in October to the second Saturday in March, with transitions at 24:00 local time. The time difference between the United Kingdom and mainland Chile may therefore be three, four, or five hours, depending on the date.

Argentina, Iceland, Saskatchewan and other areas skew time zones westward, in effect observing DST year round without complications from DST shifts. The United Kingdom and Ireland experimented with year-round DST from 1968 to 1971 but abandoned it due to its unpopularity, particularly in the north.[4] Alaska, France, Spain and other areas both skew time zones and shift clocks, in effect observing double (or more) DST in summer.

DST is generally not observed in the tropics, where day lengths do not vary enough to justify it.