Daylight Saving Time was instituted in the United States during WW1 in order to save energy for war production by taking advantage of the later hours of daylight between April and October. During World War II the federal government again required the states to observe the time change. Between the wars and after WW2,states and communities chose whether or not to observe Daylight Saving Time. In 1966, Congress passed the Uniform Time Act,which standardized the length of Daylight Saving Time.
Daylight Saving Time is four weeks longer since 2007 due to the passage of the Energy Policy Act in 2005. The Act extended Daylight Saving Time by four weeks from the second Sunday of March to the first Sunday of November, with the hope that it would save 10,000 barrels of oil each day through reduced use of power by businesses during daylight hours. Unfortunately, it is exceedingly difficult to determine energy savings from Daylight Saving Time and based on a variety of factors, it is possible that little or no energy is saved by Daylight Saving Time.
The phrase "Spring forward, Fall back" helps people remember how Daylight Saving Time affects their clocks. At 2 a.m. on the second Sunday in March, we set our clocks forward one hour ahead of Standard Time ("Spring forward"). We "Fall back" at 2 a.m. on the first Sunday in November by setting our clock back one hour and thus returning to Standard Time.