Daylight Saving Time 2012: Time to Set Clocks Back This Weekend

Nov. 3, 2012— -- You'll lose an extra hour of light but gain an hour back this weekend as daylight saving time officially ends.

As standard time resumes at 2 a.m. Sunday, it's time to "fall back," so set your clocks back one hour when you go to bed tonight.

Hawaii and most of Arizona do not observe daylight saving time.

Daylight saving time is mandated by governments, which instituted the time switch during World Wars I and II to save energy and resources for the war effort.

Previously, daylight saving time was observed in the United States from April until mid-October.

In 2007, Congress adjusted daylight saving time to begin three weeks earlier and end one week later.

At the time, it pointed to the fact that longer daylight in the evening reduced the need to turn on lights at night.

But critics questioned the government's decision and wondered whether people would turn on more lights in the morning hours instead.

In response, the Department of Energy studied the energy savings in 2008 and found that during daylight saving time, U.S. electricity use decreased by 0.5 percent per day, which added up to 1.3 billion kilowatt-hours -- enough to power about 122,000 average U.S. homes for a year.

ABC News' Ned Potter and Colleen Curry contributed to this report.