The clock tower at the Trump International Hotel at daybreak in Washington, March 9, 2018. This weekend marks the switch to daylight saving time when this and most for the rest of the clocks in the U.S. will need to be set forward an hour.
The clock tower at the Trump International Hotel at daybreak in Washington, March 9, 2018. This weekend marks the switch to daylight saving time when this and most for the rest of the clocks in the U.S. will need to be set forward an hour.

Americans will set their clocks and watches forward by an hour Sunday for daylight saving time, a practice aimed at making the most of longer periods of light during spring and summer days.

The practice, which began in Germany during World War I, was originally meant to conserve coal by reducing people's use of artificial lighting in the evenings. By the time the war ended in 1918, several other European countries had followed suit.

Critics of the practice say it does not really save energy because it leads people to use more artificial light in the dark mornings and more air conditioning during the warm evening hours.

The United States began letting individual states use daylight saving time in 1918. Only Arizona and Hawaii have opted out of the time change. The practice also has spread to the Middle East and central Asia.

Start and end dates differ, but most countries in the Northern Hemisphere begin daylight saving time in March or April and switch back in October or November. The European Union turns its clocks forward March 27.