Mornings are about to become a little brighter, and evenings a bit darker, as daylight saving time ends this weekend.

The switch goes into effect at 2 a.m. Sunday, giving us an extra hour of sleep as clocks "fall back" one hour to standard time.

The transition moves one hour of daylight from the evening to the morning, the National Institute of Standards and Technology says.

The period remains in effect until March 8, when we'll "spring ahead" again to daylight saving time, or DST.

Daylight Saving Time was introduced in 1918 and its duration was increased by about a month in 2007.

Not everyone, however, will get an extra hour to their weekends. DST isn't observed in Hawaii, American Samoa, Guam, Puerto Rico, the Virgin Islands or Arizona (other than Navajo reservations), so those places won't have a switch on Sunday.

Each switch between DST and standard time brings more debate about DST's necessity.

One expert told National Geographic that the period "isn't an energy-saving project," refuting a long-standing argument for keeping it around. A neurology professor told that the time changes can trigger cluster headaches in the fall and spring.

And even accompanied by brighter mornings, standard time's early darkness can have its own set of perils.

Some health experts say the darker evenings can lead to seasonal affective disorder and travel associations warn of more accidents during p.m. commutes.

The time shift seems to have one continuing use, at least: Emergency-management officials and fire departments, including those in the Philadelphia region, routinely use the clock changes to remind residents to check smoke alarms, restock emergency supplies, and make plans for disasters.

Contact Emily Babay at 215-854-2153 or Follow @emilybabay on Twitter.
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