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Daylight saving time (DST) or summer time is the practice of advancing clocks during summer months by one hour so that in the evening daylight is experienced an hour longer, while sacrificing normal sunrise times. Typically, regions with summer time adjust clocks forward one hour close to the start of spring and adjust them backward in the autumn to standard time.〔 New Zealander George Hudson proposed the modern idea of daylight saving in 1895.〔 Germany and Austria-Hungary organized the first nationwide implementation, starting on 30 April 1916. Many countries have used it at various times since then, particularly since the energy crisis of the 1970s. The practice has received both advocacy and criticism.〔 Putting clocks forward benefits retailing, sports, and other activities that exploit sunlight after working hours,〔 but can cause problems for evening entertainment and for other activities tied to sunlight, such as farming.〔〔 Although some early proponents of DST aimed to reduce evening use of incandescent lighting, which used to be a primary use of electricity,〔 modern heating and cooling usage patterns differ greatly and research about how DST affects energy use is limited or contradictory.〔 DST clock shifts sometimes complicate timekeeping and can disrupt travel, billing, record keeping, medical devices, heavy equipment,〔 and sleep patterns.〔 Computer software can often adjust clocks automatically, but policy changes by various jurisdictions of the dates and timings of DST may be confusing.〔 ==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 and 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, the effect becoming greater as 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 an extra hour of daylight after their workday activities. However, they will have one less hour of daylight at the start of each day, making the policy less practical during winter. 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.〔(【引用サイトリンク】url=http://www.snopes.com/science/daylight.asp )〕〔(【引用サイトリンク】url=http://www.nmm.ac.uk/explore/astronomy-and-time/time-facts/british-summer-time/ )〕 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 sync with standard working hours regardless of manipulations of the clock. DST is also of little use for locations near the equator, because these regions see only a small variation in daylight throughout the year. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Daylight saving time」の詳細全文を読む スポンサード リンク
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