What is "daylight saving time"

n. An adjustment of the official time during summer to cause events to be scheduled during daylight hours.

Daylight saving time (DST) or summer time is the practice of advancing clocks during summer months by one hour so that evening daylight lasts 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. People use the terms "spring forward" and "fall back" when referring to this.

New Zealander George Hudson proposed the idea of daylight saving in 1895. 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.

The practice has both advocates and critics. Putting clocks forward benefits retailing, sports, and other activities that exploit sunlight after working hours, but can cause problems for outdoor entertainment and other activities tied to sunlight, such as farming. Though some early proponents of DST aimed to reduce evening use of incandescent lighting—once a primary use of electricity—today's 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 often adjusts clocks automatically, but policy changes by various jurisdictions of DST dates and timings may be confusing.