Daylight saving time

World map. Europe, most of North America, parts of southern South America and southeastern Australia, and a few other places use DST. Most of equatorial Africa and a few other places near the equator have never used DST. The rest of the landmass is marked as formerly using DST.
Daylight saving time regions:
  Northern hemisphere summer
  Southern hemisphere summer
  Formerly used daylight saving or permanently daylight saving
  Never used daylight saving

Daylight saving time (abbreviated DST), commonly referred to as daylight savings time in speech, [1] and known as summer time in some countries, is the practice of advancing clocks during summer months so that evening daylight lasts longer, while sacrificing normal sunrise times. Typically, regions that use daylight saving time adjust clocks forward one hour close to the start of spring and adjust them backward in the autumn to standard time. [2]

George Hudson proposed the idea of daylight saving in 1895. [3] The German Empire and Austria-Hungary organized the first nationwide implementation, starting on April 30, 1916. Many countries have used it at various times since then, particularly since the energy crisis of the 1970s.

DST is generally not observed near the equator, where sunrise times do not vary enough to justify it. Some countries observe it only in some regions; for example, southern Brazil observes it while equatorial Brazil does not. [4] Only a minority of the world's population uses DST, because Asia and Africa generally do not observe it.

DST clock shifts sometimes complicate timekeeping and can disrupt travel, billing, record keeping, medical devices, heavy equipment, [5] and sleep patterns. [6] Computer software often adjusts clocks automatically, but policy changes by various jurisdictions of DST dates and timings may be confusing. [7]

Rationale

Industrialized societies generally follow a clock-based schedule for daily activities that do not change throughout the course of the year. The time of day that individuals begin and end work or school, and the coordination of mass transit, for example, usually remain constant year-round. In contrast, an agrarian society's daily routines for work and personal conduct are more likely governed by the length of daylight hours [8] [9] and by solar time, which change seasonally because of the Earth's axial tilt. North and south of the tropics daylight lasts longer in summer and shorter in winter, with the effect becoming greater the further one moves away from the tropics.

By synchronously resetting all clocks in a region to one hour ahead of standard time (one hour "fast"), individuals who follow such a year-round schedule will wake an hour earlier than they would have otherwise; they will begin and complete daily work routines an hour earlier, and they will have available to them an extra hour of daylight after their workday activities. [10] [11] However, they will have one fewer hour of daylight at the start of each day, making the policy less practical during winter. [12] [13]

While the times of sunrise and sunset change at roughly equal rates as the seasons change, proponents of Daylight Saving Time argue that most people prefer a greater increase in daylight hours after the typical "nine to five" workday. [14] [15] Supporters have also argued that DST decreases energy consumption by reducing the need for lighting and heating, but the actual effect on overall energy use is heavily disputed.

The manipulation of time at higher latitudes (for example Iceland, Nunavut or Alaska) has little impact on daily life, because the length of day and night changes more extremely throughout the seasons (in comparison to other latitudes), and thus sunrise and sunset times are significantly out of phase with standard working hours regardless of manipulations of the clock. [16] DST is also of little use for locations near the equator, because these regions see only a small variation in daylight in the course of the year. [17] The effect also varies according to how far east or west the location is within its time zone, with locations farther east inside the time zone benefiting more from DST than locations farther west in the same time zone. [18]

Other Languages
Afrikaans: Somertyd
العربية: توقيت صيفي
asturianu: Horariu de branu
Avañe'ẽ: Arahaku ára
azərbaycanca: Yay vaxtı
تۆرکجه: یای ساعاتی
Bân-lâm-gú: Joa̍h-tang sî-kan
башҡортса: Йәйге ваҡыт
беларуская: Летні час
беларуская (тарашкевіца)‎: Летні час
brezhoneg: Eur hañv
čeština: Letní čas
dansk: Sommertid
Deutsch: Sommerzeit
eesti: Suveaeg
Ελληνικά: Θερινή ώρα
Esperanto: Somera tempo
føroyskt: Summartíð
français: Heure d'été
Frysk: Simmertiid
Gaeilge: Am samhraidh
Bahasa Indonesia: Waktu Musim Panas
íslenska: Sumartími
italiano: Ora legale
עברית: שעון קיץ
къарачай-малкъар: Джай заман
ქართული: ზაფხულის დრო
қазақша: Жазғы уақыт
Latina: Hora aestiva
latviešu: Vasaras laiks
lietuvių: Vasaros laikas
Limburgs: Zomertied
მარგალური: ზარხულიშ ბორჯი
Bahasa Melayu: Waktu musim panas
Nederlands: Zomertijd
日本語: 夏時間
norsk: Sommertid
norsk nynorsk: Sommartid
occitan: Ora d'estiu
oʻzbekcha/ўзбекча: DST
polski: Czas letni
português: Horário de verão
Ripoarisch: Sommezick
română: Ora de vară
русский: Летнее время
саха тыла: Сайыҥҥы кэм
Seeltersk: Suumertied
Simple English: Daylight saving time
slovenčina: Letný čas
slovenščina: Poletni čas
ślůnski: Letńi czas
srpskohrvatski / српскохрватски: Ljetno vrijeme
Basa Sunda: Wanci Usum Panas
suomi: Kesäaika
svenska: Sommartid
татарча/tatarça: Җәйге вакыт
удмурт: Гужем дыр
українська: Літній час
Võro: Suvõaig
粵語: 夏令時間
žemaitėška: Vasaras čiesos
中文: 夏时制