Daylight saving time

Many countries, or even parts only of countries, adopt daylight saving time during part of the year. This typically involves advancing clocks by an hour near the start of spring and adjusting back in autumn. Some countries also use backward daylight saving over the winter period. Modern DST was first proposed in 1907 and was widespread use in 1916 as a wartime measure aimed at conserving coal. Despite controversy, many countries have used it since then; details vary by location and change occasionally.

Daylight saving time (DST; also summer time in British English) is the convention of advancing clocks so that afternoons have more daylight and mornings have less. Typically clocks are adjusted forward one hour near the start of spring and are adjusted backward in autumn. Modern DST was first proposed in 1907 by William Willett. Many countries have used it since then; details vary by location and change occasionally.

The practice can be controversial. Adding daylight to afternoons benefits retailing, sports, and other activities that exploit sunlight after working hours, but causes problems for farming, entertainment and other occupations tied to the sun. Extra afternoon daylight reduces traffic fatalities;[5] its effect on health and crime is less clear. An early goal of DST was to reduce evening usage of incandescent lighting, formerly a primary use of electricity; changes in usage patterns have cast doubt on whether DST now saves energy.

DST's clock shifts can serve as fire safety reminders, but they complicate timekeeping and can disrupt meetings, travel, billing, recordkeeping, medical devices, and heavy equipment. Many computer-based systems can adjust their clocks automatically, but this can be limited and error-prone, particularly when DST rules change.