Daylight saving time or DST is the time following the convention during which clocks are advanced to use more daylight. Usually clocks advance one hour in early spring, and are delayed again in autumn. Northern Spring begins at the end of March, while the southern spring begins at the end of September. In northern hemisphere autumn begins at the end of September, while in southern hemisphere autumn begins at the end of March.
Many ancient cultures extended daytime hours in summer. Modern daylight saving time was first proposed by Benjamin Franklin and later in 1907 by William Willett. It was widely used for the first time in 1916, during the First World War, to save coal. Despite the controversies, many countries have been using it ever since. The time details differ depending on the country and are sometimes modified.
Adding time daylight to afternoons benefits activities that favors the presence of light after work, but can cause problems in agriculture and other occupations that depend on the exposure time to sunlight. The evening increase in light can help to reduce traffic accidents, but their effects on health and the incidence of crime are less clear. It is said that daylight saving time saves electricity by reducing the need for artificial lighting, but the evidence supporting it is weak, given that summer time may stimulate the appearance of demand spikes, which increases costs.
On the other hand, schedule changes make it difficult to perceive time and can cause sleep problems for people, as well as upsetting meetings, travel, baggage check-in, record keeping, medical devices and the use of heavy machinery. Many systems run by computers are able to adjust their clocks automatically, but fail to produce errors, particularly when DST rules change.
Some ancient civilizations, such as the Egyptian, Roman and Mesopotamian, adjusted the schedules to the sun with greater flexibility than the daylight saving time, usually dividing the time of light into twelve hours of equal duration, for making the hours of light longer during the summer. For example, Romans had different scales for different months of the year.
Like ancient Rome, eighteenth century Europe had no precise timetable. However, this changed soon, since the railroad and the networks of communication made the standardization of time necessary in a way that was not known in Franklin's time.
Germany, its allies and their occupied zones were the first Europeans to use daylight saving time, which was applied for the first time in 1916. The United Kingdom and most of the other states at war and many neutral European countries followed. Russia and a few nations waited the next year, and the United States did not use it until 1918. Since then many proposals, adjustments and revocations have taken place.
Daylight saving time has caused controversy since it was first implemented. Its supporters argue that it helps increase the chances of finding happiness among the millions of people. Its critics detect the bony, bluish hand of Puritanism, anxious to bring people to bed earlier and raise them earlier, to make them healthier, richer and wiser in spite of themselves. Historically, retailers, athletes and tourists have come out in favor of daylight saving time, while farmers and the entertainment industry have opposed.
The World War I changed the balance of support, as daylight saving time was proposed to alleviate the hardships of the war in terms of saving coal and nighttime blackouts to hinder the bombings. After application by the German Empire, the United Kingdom applied for the first time the summer time in 1916. The entry into the war of the United States in 1917 provided the reasons to overcome the objections, and from 1918 summertime was applied.
The war ended, and the balance was again lowered. Farmers continued to disagree with daylight saving time, and many countries revoked it after the war. United Kingdom was an exception as it continued with summer time but for years adjusted the transition dates for a variety of reasons, including special rules during the 1920s and 1930s to avoid time changes on Easter mornings.
United States was more conventional. Congress revoked it in 1919. President Woodrow Wilson vetoed the revocation twice, but his second veto was overturned, and only a few cities of the country conserved locally the summer time.