When local time on Sunday, March 10, is 2 a.m., the clocks will turn forward one hour to 3 a.m. The time of sunrise and sunset will then be an hour later than the previous day, and there will be more light in the evening.

Standard time will move to daylight saving time (DST), or summer time, as it’s known in Europe. The change forward, applied in the spring, and back, applied in the fall, is intended to make better use of sunlight. Even though different countries have different dates for changing the clock, the idea is the same — to have as much daylight as possible.

Benjamin Franklin is often credited as the first person to propose changing the time in his 1784 essay “An Economical Project.” The idea was seriously considered more than a century later, when William Willetts, a British builder, fiercely advocated for it. His argument was that people like long evenings because they can do more, and that they regret missing the opportunity to make the most of bright mornings in the summer as they are still sleeping.

Different acts were passed in Germany and Great Britain over the years. The countries applied various schemes of moving the clock forward and back — sometimes by minutes a few weeks in a row and sometimes choosing a fixed day for summer times.

Daylight saving time, as we know and use it today, was suggested by an entomologist from New Zealand, George Hudson. In 1895, he recommended a two-hour time change because he wanted to have more daylight after work to go hunting for bugs in the summer.

The benefits of DST were first recognized during World War I, when Germany was looking for ways to save energy. Germany moved the clock forward to have more daylight while people were at work. Several countries, including the United States in 1918, followed suit. DST was used again in World War II as a way to save energy for war production. To avoid confusion among states about changing dates, a federal law was passed in 1966 standardizing the length and times of DST for the country.

Nowadays, the use of DST has become controversial because it no longer saves energy, certainly not as much as a century ago. While people may delay switching the lights on in the evening, they are using electricity during dark mornings.

Geography is an important factor as well. Many countries in the Southern Hemisphere — especially those along and below the equator — don’t use daylight saving time at all because the hours of sunlight they get every day barely vary throughout the year — about 12 hours. The farther countries are from the equator, the less sunlight they get during the day. Hawaii, Arizona (except the Navajo Nation), and overseas U.S. territories don’t observe DST.

Of the large countries in South America, only Brazil and Chile enact DST. Australia does not have a federal rule; it’s up to separate regions to decide. Western Australia, Queensland, and the Northern Territory don’t observe DST. Neither do China, Japan, South Korea, Taiwan, South Africa, and India. In Europe, the most famous example of a country that chooses not to turn its clock forward or back is Iceland, despite its far northern location.

Another movement against DST focuses on negative health outcomes. Cluster headaches are more likely within two week of the day time changes, and people are more prone to car crashes because of the one less hour of sleep. The incidence of heart attacks may also increase as a result of the time change in March, and more people seek help for depression over approximately 10 weeks after the transition from summer to standard time.

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