How does dst work

Energy Policy Act thoughtfully provides rules to standardize the implementation of daylight saving time, it doesn't require all states to follow them. In fact, any state or territory can apply for an exemption and, if it's granted, sidestep DST and remain on standard time throughout the year.

Indiana, which used to observe DST in only 15 of its 90 counties, now "springs forward" and "falls back" across the whole state. Don't think Americans are alone in their zeal to stretch out summer days.

Many other countries practice daylight saving time in some fashion. European nations have been taking advantage of what they call "summer time" for decades, but they didn't standardize it until , when the European Union adopted a common DST schedule that runs from the last Sunday in March through the last Sunday in October.

It can be hard enough to remember your own age sometimes, let alone which countries do and don't observe daylight saving time. The WorldClock is happy to help you out here. The site lists the current local times in major cities around the world and notes which times have been adjusted for daylight saving time.

Regardless of the specific rules implemented by a country, starting and stopping DST works the same way. A popular start time is 2 a. At that time, the clock moves forward exactly one hour.

Here's a second-by-second account of what occurs:. Notice that every second between and disappears completely. To start DST, a full hour must be skipped! In the fall, when daylight saving time ends, you get the lost hour back because the time from to is repeated for one day. Here's what it looks like:. Notice that the clock moves from to , not In other words, one full hour occurs twice, and the day ends up being 25 hours long. Most people don't ever need to refer to time within this hour, but if they do, say, because a birth or death occurred, they need to mention whether it was before or after the change back to standard time.

It's taken a few years -- and several changes -- to perfect this time-switching model. In the next section, we'll look at the history of daylight saving time to understand how it's evolved. More than a century after eager beaver Ben Franklin conceived of daylight saving time, other folks, like New Zealander George Vernon Hudson and Englishman William Willett, had the same idea.

Willett penned a pamphlet in called "The Waste of Daylight," in which he proposed that, during the spring and summer months, British clocks be moved ahead by 80 minutes in four minute increments. In , the House of Commons said thanks but no thanks to Willett's plan. And so clocks ticked off standard time in the world for another 10 years.

Then, the first of two global conflicts saw widespread fighting and forced many governments to consider drastic energy-cutting measures. Germany adopted daylight saving time or war time rules in in an effort to preserve its supplies of coal. England quickly followed suit, introducing British summer time and moving all clocks one hour ahead of Greenwich Mean Time during the summer months. In total, 31 nations, including the United States, began shifting their clocks to make better use of daylight hours and to preserve resources for the war effort.

After the war, most countries repealed their DST laws and returned to standard time. Peace, of course, didn't last. When World War II began in , governments once again recognized the value of daylight saving time and implemented appropriate rules. This time, 52 countries shifted their clocks forward, some during the summer months, others for the whole year.

The U. After the war, Congress repealed mandatory DST, but left it up to different states and localities to decide whether they would continue the practice.

Some did. Some didn't. Finally, in , the U. These rules were contained in the Uniform Time Act , which set the beginning and ending of DST, as well as the time when the changeover should occur. For the next 20 years, all was calm on the U.

In , U. President Ronald Reagan tweaked daylight saving time when he signed Public Law According to language in the law, the edit was made to provide "more daylight outdoor playtime for the children and youth of our Nation, greater utilization of parks and recreation areas, expanded economic opportunity through extension of daylight hours to peak shopping hours and through extension of domestic office hours to periods of greater overlap with the European Economic Community.

This went into effect in That same year, the entire state of Indiana started observing DST before, only parts of the state did. Advocates of daylight saving time have always pointed to energy conservation as the most important reason to move clocks forward during summer months. Here's the theory: Because 25 percent of all electricity consumed goes to powering lamps and small appliances, having more daylight hours for at least half the year should reduce the amount of electricity we use for lighting and running TVs, DVD players and stereos [source: Aldrich ].

Also, DST should serve as an incentive for people to spend more time outdoors. In other words, there's more daylight available after school and work to go for a walk, play tennis or hit the links.

If people are outside, they're not inside turning on lamps, appliances and electronics. It wasn't until the early s, however, that the power-conservation theory was put to the test. Department of Transportation was required to study the effect of DST on electricity demand. To do this, researchers analyzed electricity load data from 22 different utilities for a period of days before and after transitions in and out of DST.

Their report, published in , found that daylight saving time reduced national electricity usage by roughly 1 percent compared with standard time. This study stood as gospel for years, with little research conducted to support or refute it. As DST starts, the Sun rises and sets later, on the clock, than the day before. When DST starts in the spring, our clocks are set forward by a certain amount of time, usually by one hour.

This means that one hour is skipped, and on the clock, the day of the DST transition has only 23 hours. Since DST switches usually occur at night to avoid disrupting public life, they snatch away an hour of our usual sleeping time, forcing us to adjust our body clocks. If you set your alarm to the same time as before the clock change, you will sleep an hour less.

The good news is that if you work a night shift, you will get away with working one hour less that night. The DST period in the United States begins at 2 am local time, so the hour from to does not exist in the night of the switch. It is skipped as clocks spring forward from standard time to Daylight Saving Time see table. Note: the DST period may begin and end at different local times in other countries, but the principle is the same.

In the fall autumn , the DST period usually ends, and our clocks are set back to standard time again. In terms of hours on the clock, we gain one hour, so the day of the transition is 25 hours long.

In March , a Rasmussen Report surveying U. Surprisingly, there are some risks associated with making the change. Some studies have shown that there could actually be health risks associated with the time change, such as increased traffic accidents and instances of heart attack, according to National Geographic and Reuters.

A National Bureau of Economic Research study that analyzed the time change in Indiana, noted that while residents used less lights in the evening, they turned up their air conditioning, offsetting any energy savings entirely. Additionally, several studies have shown Americans actually increase their energy consumption during daylight saving time. The extra hour of daylight often means that people will often head out to do outdoor activities.

Often, that involves getting in the car and going for a drive, which burns fuel and released greenhouse gases into the air. Type keyword s to search. Today's Top Stories.

Three Lions Getty Images. So, if you happen to be traveling, make sure you double check before times. Hulton Archive Getty Images. Messing With Time. Jennifer Leman Jennifer Leman is a science journalist and news editor at Popular Mechanics, where she writes and edits stories about science and space. This content is created and maintained by a third party, and imported onto this page to help users provide their email addresses.

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