If you're worried about staying out too late tonight celebrating Halloween, rest easy. You can sleep in Sunday.

Residents of Utah and most surrounding states gain an hour when we revert to Mountain Standard Time at 2 a.m.

Nowadays, the time change occurs three weeks later than it did before 2007. Congress, in a 2005 law, extended daylight saving time in an effort to conserve energy.

Those of us who've been stumbling to work or school in the dark this month wonder whether the delay is worth it.

It's one of several questions that arise with each time change:

Does extending daylight saving time save energy?

Maybe. Daylight saving time is believed to trim the nation's energy use because usage declines when there's less time between sunset and bedtime.

However, a 2008 National Bureau of Economic Research study in Indiana concluded the practice may actually increase usage because people use fewer lights but more heating and cooling.

Critics say results in Indiana may not prove true nationwide. The Department of Energy is conducting the first national study of the issue since the 1970s but has yet to release results.

Who thought this up in the first place?

Ben Franklin is credited with the idea of establishing daylight saving time, which is practiced in some form in more than 70 countries. In the U.S., it wasn't until 1966 that Congress passed the first federal daylight saving time law that wasn't part of a wartime initiative. Since then, the law has changed a number of times. The practice remains controversial.

Will the law change again?

The Web site standardtime.com engages in a perpetual campaign to urge Congress to do away with daylight saving time. The effort does have some congressional support, but only time will tell.

Sources » National Bureau of Economic Research, California Energy Commission