Daylight saving time is the convention of advancing
clocks so that afternoons have more
daylight and mornings have less. Typically clocks are adjusted forward one hour near the start of
spring and are adjusted backward in
autumn; the ancients lengthened summer hours instead. Presaged by a 1784
satire, modern DST was first proposed in 1907 by
William Willett, and 1916 saw its first widespread use as a
wartime measure aimed at
conserving coal. Despite controversy, many countries have used it since then;
details vary by location and change occasionally. Adding daylight to afternoons benefits
retailing,
sports, and other activities that exploit
sunlight after working hours, but causes problems for
farmers and other workers whose hours depend on the sun. Extra afternoon daylight cuts
traffic fatalities; its effect on
health and
crime is less clear. DST is said to save
electricity by reducing the need for artificial evening
lighting, but the evidence for this is weak and DST can boomerang by boosting
peak demand, increasing overall electricity costs. DST's clock shifts complicate
timekeeping and can disrupt meetings, travel, billing, medical devices, and heavy equipment.
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