Daylight saving time

Daylight saving time, method of making better use of daylight by setting clocks 1 hour ahead of standard time. Daylight saving time came into use in the United States and other countries during World War I, in an effort to conserve electricity by having business hours correspond more closely to the hours of natural daylight. It was again put into effect on a national scale during World War II, after which the matter was left to the discretion of local authorities. Daylight saving time in the United States now extends from the second Sunday in April to the last Sunday in October.