Sunday morning, everyone gets an extra hour of sleep.

Daylight saving time, which has allowed us to enjoy the days of summer, comes to an end Sunday at 2 a.m., when people will set their clocks back one hour — following the old saying, “Spring forward, fall back” — giving them an extra hour of sleep.

The U.S. first adopted daylight saving time near the end of World War I and then again during World War II. It became law in 1966 when President Lyndon Johnson signed the Uniform Time Act to establish uniform dates for observing daylight saving time.

Some states will not change time Sunday. Hawaii and Arizona (excluding the Navajo Nation), American Samoa, Guam, Puerto Rico, the Virgin Islands and the Northern Mariana Islands do not observe daylight saving time.

According to a 2008 Department of Energy report, experts studied the impact of the extended daylight saving time on energy consumption in the U.S. and found the extra four weeks of daylight saving time saved about 0.5 percent in total electricity per day.

That added up to electricity savings of 1.3 billion kilowatt-hours —the amount of electricity used by more than 100,000 households for an entire year.