Benjamin Franklin  was among the first Americans to discuss the idea of Daylight Saving Time. In fact, he proposed the idea while serving as U.S. minister to France as a way of conserving the cost of lighting for shops. The purpose has been to essentially utilize more of the daylight hours in spring and summer for daytime activities. Simply put, the Sun is up longer in the sky (rises earlier and sets later) in summer. Clocks and common mechanical timepieces keep what's called civil time, which roughly corresponds to the passage of a fictitious "average" Sun through our sky. This is necessary since the Sun does not rise and set on a regular basis, but changes by as much as 15 minutes throughout the course of the year.\n\nDaylight Saving Time was generally adopted by countries around World War I, but President Wilson repealed the United States' mandatory daylight savings law on March 31, 1918. During World War II, Daylight Savings Time was reestablished by law on a year-round basis, and later seen as a fuel saving measure during the Arab Oil Embargo crisis of 1973-74. In late 1974, standard time was brought back. During World War II, the U.S. and some other countries implemented "double" daylight savings time consisting of a two hour shift.
What's the basis for Daylight Savings Time?