This past weekend we set our clocks back one hour as we do every year. Ideally when we get up in the morning it will be a little lighter, and, not so ideally, after we work we'll all be stumbling home in the dark. But why do we do this? Supposedly Benjmain Franklin first proposed daylight saving time (DST) as a way to save candles, but he also suggested waking the public by firing cannons at sunrise, so it's difficult to say how serious he was. The idea in its modern systematized form was first proposed in 1895 at a meeting of the Wellington Philosophical Society by George Vernon Hudson, a New Zealand entymologyst, as a way of maximizing the number of daylight hours people spend at work, and, presumably, lower energy costs for places of employment. It makes sense: if you're looking for ideas that will interfere with everyone's body clocks and make commuters morose, just ask your local entymologyst, right?
Germany adopted DST in 1916 to conserve fuel for the war effort. The U.S. Congress adopted daylight saving time in 1918, but it proved to be extremely unpopular and the law was repealed a year later. Then we fast-forward 24 years, when DST was again passed by Congress as a wartime economy measure. And it was actually called as "War Time" and not daylight saving time. This second DST law mandated the practice would expire six months after the war.
Since then the legal history of DST in the US has been a little complicated, but the bottom line is any state or territory can opt out of DST. Hawaii, Arizona, American Samoa, Puerto Rico and the U.S. Virgin Islands do not observe DST.
But what does daylight saving time accomplish? No one actually knows if it saves energy. According to a 2008 study of electric utilities across the country, DST saves 0.5 percent of the nation's electricity per day. On the other hand, after Indiana adopted DST in 2006, economists found a 1% rise in electricity use in the state. And a 2016 study found links between DST and increased incidence of heart attacks and workplace injuries.