Daylight saving time (DST) or summer time (see Terminology) is the practice of advancing clocks during the lighter months so that evenings have more apparent daylight and mornings have less. Typically clocks are adjusted forward one hour near the start of spring and are adjusted backward in the autumn.
The modern idea of daylight saving was first proposed in 1895 by George Vernon Hudson and it was first implemented by Germany and Austria-Hungary starting on 30 April 1916. Many countries have used it at various times since then, most consistently since the energy crises of the 1970s.
The practice has been both praised and criticized. Adding daylight to evenings benefits retailing, sports, and other activities that exploit sunlight after working hours, but can cause problems for evening entertainment and other occupations tied to the sun (such as farming) or to darkness (such as firework shows).Although an early goal of DST was to reduce evening use 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 or contradictory.
DST clock shifts present other challenges. They complicate timekeeping, and can disrupt meetings, travel, billing, record keeping, medical devices, heavy equipment, and sleep patterns. Software can often adjust computer clocks automatically, but this can be limited and error-prone, particularly when DST dates are changed.