<P> The period of Daylight Saving Time before the longest day is shorter than the period after, in several countries including the United States and Europe . For example, in the U.S. the period of Daylight Saving Time is defined by the Energy Policy Act of 2005 . The period for Daylight Saving Time was extended by changing the start date from the first Sunday of April to the second Sunday of March, and the end date from the last Sunday in October to the first Sunday in November . </P> <P> DST's potential to save energy comes primarily from its effects on residential lighting, which consumes about 3.5% of electricity in the United States and Canada . (For comparison, air conditioning uses 16.5% of energy in the United States .) Delaying the nominal time of sunset and sunrise reduces the use of artificial light in the evening and increases it in the morning . As Franklin's 1784 satire pointed out, lighting costs are reduced if the evening reduction outweighs the morning increase, as in high - latitude summer when most people wake up well after sunrise . An early goal of DST was to reduce evening usage of incandescent lighting, once a primary use of electricity . Although energy conservation remains an important goal, energy usage patterns have greatly changed since then . Electricity use is greatly affected by geography, climate, and economics, so the results of a study conducted in one place may not be relevant to another country or climate . </P> <Ul> <Li> In the United States, high - quality research indicates that DST reduces residential lighting costs but usually increases total energy consumption, especially when non-electricity sources of energy consumption are considered . These non-electricity sources of energy consumption include extra heating fuel on the colder, darker mornings and extra gasoline used to drive to shopping and sporting activities . In some cases, DST increases residential electricity consumption, such as when people use more air conditioning in the longer, hotter evenings . </Li> <Li> A 2007 study estimated that winter daylight saving would prevent a 2% increase in average daily electricity consumption in Great Britain . This paper was revised in October 2009 . </Li> <Li> In 2000, when parts of Australia began DST in late winter, overall electricity consumption did not change, but the morning peak load and prices increased . The overall consumption was the same because people used more electricity in the dark mornings, and correspondingly less electricity in the brighter evenings . In Western Australia during summer 2006--2007, DST increased electricity consumption during hotter days and decreased it during cooler days, with consumption rising 0.6% overall . </Li> <Li> Although a 2007 study estimated that introducing DST to Japan would reduce household lighting energy consumption, a 2007 simulation estimated that DST would increase overall energy use in Osaka residences by 0.13%, with a 0.02% decrease due to less lighting more than outweighed by a 0.15% increase due to extra cooling; neither study examined non-residential energy use . This is probably because DST's effect on lighting energy use is mainly noticeable in residences . </Li> </Ul> <Li> In the United States, high - quality research indicates that DST reduces residential lighting costs but usually increases total energy consumption, especially when non-electricity sources of energy consumption are considered . These non-electricity sources of energy consumption include extra heating fuel on the colder, darker mornings and extra gasoline used to drive to shopping and sporting activities . In some cases, DST increases residential electricity consumption, such as when people use more air conditioning in the longer, hotter evenings . </Li>

When are clocks changed for daylight savings time