Does Daylight Saving Time work?

  Most Americans woke up a little bit groggier this past Sunday. Thanks to daylight saving time, or DST, clocks in most parts of the United States were set one hour ahead—robbing millions of precious sleep but rewarding them with extra daylight in return.

  The interval for DST has been longer in the past four years. That’s because the Energy Policy Act of 2005 mandated that DST be extended by one month. It used to last from the first Sunday in April to the last Sunday in October, but now lasts from the second Sunday in March until the first Sunday in November.

  Why the switch? Or, more to the point, why have DST at all? The answer lies in the desire to conserve energy. DST proponents argue that waking up earlier to take advantage of the increased daylight reduces the need for artificial forms of lighting—and they have been making this argument for literally hundreds of years.