ACADEMIC AMERICAN ENCYCLOPEDIA
 
DAYLIGHT SAVING TIME
 
Daylight Saving Time (DST) provides more usable hours of
daylight for human activities by setting clocks ahead one hour
in the spring.  Although the total amount of daylight remains
the same, more daylight hours are allowed for outdoor work and
recreation in the late afternoon and evening.  Daylight Saving
Time can also reduce power requirements for lighting.  In most
parts of the United States, year-round Daylight Saving Time was 
adopted during World War II.  Now it is in effect only during
that part of the year when daylight hours are the longest.
Congress fixed this period as extending, as of 1987, from the
first (previously the last) Sunday in April to the last Sunday
in October.  Daylight Saving Time was extended during 1974 and
1975 because of the U.S.  energy crisis.