Want to know where DST comes from?
The main purpose of Daylight Saving Time (called "Summer Time" many places in the world) is to make better use of daylight.
Daylight Saving Time also saves energy.
There is a small public health benefit to Daylight Saving time.
Early laws in Britain
A bill was drafted in 1909 and introduced in Parliament several times, but it met with ridicule and opposition, especially from farming interests. Generally lampooned at the time, Willett died in 1915, but a year later Daylight Saving Time (Summer Time) was adopted in England in May 1916, following the lead of Germany. The motivation was to conserve coal. There was a fair bit of opposition from agricultural interests who wanted daylight in the morning, but Lord Balfour came forward with a unique concern.
His campaign led to the introduction of British Summer Time in an Act of Parliament in 1916. Clocks were put one hour ahead of Greenwich Mean Time (GMT) during the Summer months. The energy saving benefits of this were recognized during World War II, when clocks were put two hours ahead of GMT during the Summer. This became known as Double Summer Time. During the war, clocks remained one hour ahead of GMT throughout the winter.
Early adoption and U.S. law
Daylight saving has been used in the United States and in many European countries since World War I, when the system was adopted in order to conserve fuel needed to produce electric power. In 1918, in order to conserve resources for the war effort, Congress placed the country on Daylight Saving Time for the remainder of WW 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so unpopular (mostly because people rose earlier and went to bed earlier than we do today) that the law was later repealed in 1919 over President Wilson's veto. It was continued in a few states (Massachusetts, Rhode Island) and some cities (New York, Philadelphia, Chicago, and others).
During World War II, the United States observed year-round Daylight Saving Time (from February 2nd, 1942 to September 30th, 1945). From 1945 to 1966, there was no federal law about Daylight Saving Time. So, states and localities were free whether to observe or not to observe Daylight Saving Time and could choose when it began and ended. This, however, caused confusion -- especially for the broadcasting industry, and for railways, airlines, and bus companies. Because of the different local customs and laws, radio and TV stations and the transportation companies had to publish new schedules every time a state or town began or ended Daylight Saving Time.
Daylight Saving Time, for the U.S. and its territories, is NOT observed in Hawaii, American Samoa, Guam, Puerto Rico, the Virgin Islands, the Eastern Time Zone portion of the State of Indiana, and the state of Arizona (not the Navajo Indian Reservation, which does observe). Navajo Nation participates in the Daylight Saving Time policy, due to its large size and location in three states.

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