Daylight saving time
Although not used by most of the world’s people, daylight sav-
ing time is common in high latitudes.
DST never used
Daylight saving time (DST; also summer time in British
English—see Terminology) is the convention of advancing
clocks so that afternoons have more daylight and morn-
ings have less. Typically clocks are adjusted forward one
hour near the start of spring and are adjusted backward
in autumn. Modern DST was first proposed in 1895 by
George Vernon Hudson, a New Zealand entomologist.
Many countries have used it since then; details vary by
location and change occasionally.
The practice is controversial. Adding daylight to
afternoons benefits retailing, sports, and other activities
that exploit sunlight after working hours, but causes
problems for farming, evening entertainment and other
occupations tied to the sun. Traffic fatalities are re-
duced when there is extra afternoon daylight; its ef-
fect on health and crime is less clear. Although an early
goal of DST was to reduce evening usage of incandescent
lighting, formerly a primary use of electricity, modern
heating and cooling usage patterns differ greatly, and
research about how DST currently affects energy use is
limited and often contradictory.
DST’s occasional clock shifts present other chal-
lenges. They complicate timekeeping, and can disrupt
meetings, travel, billing, recordkeeping, medical devices,
heavy equipment, and sleep patterns. Many
computer-based systems can adjust their clocks auto-
matically, but this can be limited and error-prone, par-
ticularly when DST rules change.
Although not punctual in the modern sense, ancient
civilizations adjusted daily schedules to the sun more
flexibly than modern DST does, often dividing daylight
into twelve equal hours regardless of day length, so that
each daylight hour was longer during summer. For
example, Roman water clocks had different scales for
different months of the year: at Rome’s latitude the