DST is most commonly used in temperate regions, due to the considerable variation in the amount of daylight versus darkness across the seasons in those regions.
Governments often tout it as an energy conservation measure, on the grounds that it allows more effective use of natural sunlight resource in summer time. Since there is less darkness in the "waking day", there is less use of electric lights.
Europeans commonly refer to the system as summer time: Irish Summer Time, British Summer Time, and European Summer Time. This is reflected in the time zones names as well, e.g., Central European Time (CET) becomes Central European Summer Time (CEST). >
The word "summer" in this context includes most of spring after the spring equinox and nearly all of autumn (April through October). Likewise, the word "winter" here includes part of autumn and a few weeks in spring (November through March). This varies by time zone, of course, and can change over time as well.
It was first seriously proposed by William Willett in the "Waste of Daylight", published in 1907, but he was unable to get the British government to adopt it, despite considerable lobbying.
The idea of DST was first put into practice by the German government during the First World War, between April 30 and October 1, 1916. Shortly afterward, the United Kingdom followed suit, first adopting it between May 21 and October 1, 1916. On March 19, 1918, the U.S. Congress established several time zones (which had been in use by railroads and most cities since 1883) and made DST official, effective 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proved so unpopular (mostly because people rose and went to bed earlier than in current times) that it was later repealed.