Daylight saving time

  

Daylight saving time regions:

Daylight Saving Time (DST), also known as daylight savings, daylight time (in the U.S. and Canada), or summer time (in the U.K., EU, and other regions), involves adjusting clocks forward to make better use of extended daylight during summer months, so that evenings remain lighter for longer. Typically, clocks are moved forward by one hour in the spring or late winter, and set back to standard time in the fall. This practice is often remembered by the phrase “spring forward, fall back.”

Daylight Saving Time (DST) is rarely practiced near the Equator, where daylight hours remain relatively constant year-round. Conversely, it is often skipped in regions with extreme latitude, where one-hour adjustments bring minimal benefit due to substantial variations in daylight hours across seasons. As a result, only a small portion of the global population observes DST, and even within some countries, only certain areas participate. For instance, in Australia, DST is observed by four states and one territory, while in the U.S., all states except Hawaii and Arizona (except the Navajo Nation within Arizona) observe it.

Historically, ancient civilizations adapted their timekeeping to the seasonal changes in daylight, though they typically adjusted the lengths of hours rather than moving clocks. The Romans, for example, modified water clocks for seasonal shifts. In 1784, Benjamin Franklin humorously suggested in a Paris newspaper that earlier rising in summer could save on candles and oil, though he didn’t advocate adjusting clocks. Later, in 1895, New Zealand’s George Hudson made a practical proposal to advance clocks by two hours each spring, though it wasn't widely implemented until 1928. In 1907, British builder William Willett proposed British Summer Time as an energy-saving measure, and though it gained interest, it wasn’t enacted until 1916.

The first recorded use of DST occurred locally in Port Arthur (now part of Thunder Bay), Ontario, Canada, in 1908. The first nationwide adoption came with the German and Austro-Hungarian Empires on April 30, 1916. Since then, many countries, especially during and after the energy crisis of the 1970s, have introduced DST to conserve energy.

Rationale

In industrialized societies, daily routines are generally tied to fixed clock-based schedules, such as the start and end times for work or school, and the coordination of public transportation, which remain consistent throughout the year. This differs from agrarian societies, where activities are often aligned with natural daylight hours and solar time, both of which vary with the Earth's tilt and shift seasonally. North and south of the tropics, daylight extends longer in summer and shortens in winter, with the effect becoming more pronounced as one moves further from the equator. Because of the minimal daylight variation year-round near the equator, DST has limited benefits in these areas.

When clocks are set an hour forward in spring, individuals on a clock-based schedule wake up and start their day one hour earlier according to solar time. This adjustment allows them to complete work routines earlier, generally providing an extra hour of daylight after the workday.

Advocates of DST believe that most people prefer extra daylight hours after a standard "nine-to-five" schedule. Supporters also claim DST can reduce energy usage by decreasing the need for artificial lighting and heating, though the actual impact on energy savings is debated. 

DST also aims to improve practicality. For example, during the summer solstice in the American temperate zones, the sun rises around 4:30 a.m. and sets around 7:30 p.m. Since many people are asleep at 4:30 a.m., resetting the clock to treat 4:30 as 5:30 enables people to wake closer to sunrise and enjoy more evening light.

Variation within a time zone

The impact of Daylight Saving Time (DST) also depends on how far east or west a location sits within its time zone. Locations farther east in a time zone typically experience greater benefits from DST than those farther west. For example, although China spans thousands of kilometers, the entire country operates under a single time zone by government mandate, which reduces any advantages DST might offer.

History

Ancient civilizations adapted daily schedules to the sun in a way that was often more flexible than modern DST. They commonly divided daylight into 12 "hours" that varied in length with the seasons—becoming longer in spring and shorter in autumn. For example, the Romans used water clocks with different scales for each month; at Rome's latitude, the third hour after sunrise (hora tertia) would start at 09:02 solar time and last 44 minutes during the winter solstice, but at the summer solstice, it would start at 06:58 and last 75 minutes. From the 14th century onward, standard civil hours replaced these variable hours, and civil time no longer changed with the seasons. However, unequal hours are still used in certain traditional contexts, like the monasteries of Mount Athos and some Jewish ceremonies.

Benjamin Franklin popularized the saying "early to bed and early to rise makes a man healthy, wealthy, and wise" and, during his time as an American envoy to France (1776–1785), published a humorous letter in the *Journal de Paris* suggesting that Parisians save candles by waking earlier to make use of the morning sunlight. His satirical proposal included taxing window shutters, rationing candles, and even waking the public by ringing church bells and firing cannons at sunrise. Although Franklin is sometimes credited with inventing DST, he did not actually propose changing the clocks, as precise schedules were uncommon in 18th-century Europe. However, the need for standardized time grew with the advent of railways and communication networks.

In 1810, Spain’s National Assembly, the Cortes of Cádiz, issued a regulation that shifted certain meeting times forward by one hour from May to September to account for seasonal daylight changes, though it did not involve changing clocks. Private businesses, meanwhile, often adjusted their hours to align with daylight, but this was done voluntarily.

New Zealand entomologist George Hudson was the first to propose modern Daylight Saving Time (DST). Working a shift schedule allowed him extra daylight hours to collect insects, which led him to appreciate evening daylight. In 1895, he presented a paper to the Wellington Philosophical Society suggesting a two-hour shift in daylight hours, which gained interest in Christchurch. He expanded on his idea in a follow-up paper in 1898.

Many credit English builder and outdoorsman William Willett with independently conceiving DST. In 1907, inspired by a pre-breakfast ride where he noticed how many Londoners slept through much of the summer morning, Willett proposed advancing clocks during summer months. An avid golfer, Willett disliked cutting short his rounds at dusk, which further motivated his proposal. He published his idea two years later.

Robert Pearce, a Liberal Party MP, championed Willett’s proposal by introducing the first Daylight Saving Bill to the British House of Commons on February 12, 1908. Though a select committee was formed to review the idea, Pearce’s bill—and several subsequent ones—failed to pass. Willett continued to promote DST in the U.K. until his death in 1915.

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Port Arthur, Ontario, Canada, was the first city worldwide to implement Daylight Saving Time (DST) on July 1, 1908. Orillia, Ontario, followed soon after, introduced by Mayor William Sword Frost between 1911 and 1912. The first countries to adopt DST nationally were the German Empire and its World War I ally Austria-Hungary on April 30, 1916, to conserve coal during the war. Britain, its allies, and several neutral European nations quickly followed suit, while Russia and other countries waited until the following year, and the United States adopted DST in 1918. Though most jurisdictions discontinued DST post-war, Canada, the United Kingdom, France, Ireland, and the United States maintained it. DST returned during World War II—some countries even implemented "double summer time"—and the practice was standardized in the U.S. by federal law in 1966 and later spread across Europe in the 1970s amid an energy crisis. Since then, DST has seen multiple enactments, adjustments, and repeals worldwide.

Contrary to popular belief, DST was not originally introduced to benefit farmers. In fact, farmers have historically opposed DST, as their schedules—affected by factors like morning dew and the natural readiness of dairy cattle for milking—are determined by sunlight, making clock changes disruptive.

In the U.S., DST was first introduced under the Standard Time Act of 1918 as a temporary measure to conserve energy resources during World War I, with DST in effect for seven months. During World War II, DST was reintroduced year-round under the term "War Time." After the war, local jurisdictions decided independently whether to observe DST until the Uniform Time Act of 1966 standardized the practice. In 1974, year-round DST was briefly enacted due to the energy crisis, but it was repealed the following year after public concerns about children going to school and workers commuting in the dark during winter mornings.