Daylight saving time (DST)

At 2:00 am local today, most of the United States (except Hawaii and Arizona) will leave daylight saving time behind and fall back an hour to standard time.

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. Modern DST was first proposed in 1907 by the English builder William Willet. 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, entertainment and other occupations tied to the sun. Traffic fatalities are reduced when there is extra afternoon daylight; its effect on health and crime is less clear. Although an early goal of DST was to reduce evening usage of incandescent lightning, formerly a primary use of electricity, modern heating and cooling usage patterns greatly differ and research about how DST currently affects energy use is limited and contradictory.