Daily Dose of Insight - Daylight Savings Time

The idea of daylight saving time was first put into practice by the German government during the First World War between April 30, 1916 and October 1, 1916. Shortly afterward, the United Kingdom followed suit, first adopting DST between May 21, 1916 and October 1, 1916. Then on March 19, 1918 the U.S. Congress established several time zones (which were already in use by railroads and most cities since 1883) and made daylight saving time official (which went into effect on March 31) for the remainder of World War I. It was observed for seven months in 1918 and 1919. The law, however, proved so unpopular (mostly because people rose earlier and went to bed earlier than in modern times) that the law was later repealed.

Daylight saving time was reinstated in the United States on February 9, 1942, again as a wartime measure to conserve resources, this time in order to fight World War II. This remained in effect until the war began winding down and the requirement was removed on September 30, 1945.

Rationales for DST

One of the major reasons given for observing DST in the United States is energy conservation. Theoretically, the amount of residential electricity needed in the evening hours is dependent both on when sunset is and on when people go to bed. Because people tend to observe the same bedtime year-round, by artificially moving sunset one hour later, the amount of energy used is theoretically reduced. United States Department of Transportation studies showed that DST reduces the country's electricity usage by one percent each day.

Part of the reason that it is normally observed in the late spring, summer, and early autumn is because during the winter months the amount of energy saved by moving sunset one hour later is negated by the increased need for morning lighting by moving sunrise by the same amount. During the summer most people would wake up after the sun rises, regardless of whether daylight saving time is in effect or not, so there is no increased need for morning lighting to offset the afternoon energy savings.

Another perceived benefit of DST is increased opportunities for outdoor activities. Most people plan outdoor activities during the increased hours of sunlight. Other benefits cited include prevention of traffic injuries (by allowing more people to return home from work or school in daylight), and crime reduction (by reducing people's risk of being targets of crimes that are more common in dark areas).

Criticism of DST

DST is not universally accepted; many localities do not observe it. Opponents claim that there's not enough benefit to justify needing to adjust clocks twice per year. The disruption in sleep patterns associated with setting clocks forward, and thereby "losing" an hour, correlates with a spike in the number of severe auto accidents, as well as emotional trauma and lost productivity as tired workers adjust to the schedule change.

There is also a question whether the savings in lighting costs (people just home from work don't turn on the electric lights because there is enough sunlight through the windows) justifies the increase in summertime air conditioning costs (people home from work do turn up the air conditioning during the late-afternoon peak load times, because it's still warm outside). When air conditioning was not widely available, the change did save energy; however, air conditioning is much more widespread now than it was several decades ago.

Full story:

http://en.wikipedia.org/wiki/Daylight_savings_time