(CNN)It’s that time of the year again. You wake up and see your kitchen clock reading 8 a.m., even though you swear your alarm was set for 7 a.m. You’re convinced you’re late to work.
But wait, whew.
You’re not late. It’s Daylight Saving Time.
Twice a year, clocks around the world move forward or backward by an hour.
But what’s the point?
There’s an age-old myth that Daylight Saving was a practice adopted to give farmers extra time in the sun to work out in the field. But, that’s not really why dozens of countries follow it.
Daylight Saving Time (DST) is a system to reduce electricity usage by extending daylight hours. For eight months out of the year, the US and dozens of other countries follow DST, and for the remaining four months, revert back to standard time in order to take full advantage of the sunlight.
On the second Sunday of March at 2 a.m., clocks move forward one hour. Then, on the first Sunday of November at 2 a.m., the clocks turn back an hour. A good way to remember it? The time shifts match the seasons: Clocks “spring” forward an hour in March and “fall” back in November.
In the summer months, the sun is out for longer periods of time, so you can *rely on daylight to avoid switching lights on. The clocks revert back to standard time for the winter months so the sun can rise earlier and the world starts the day off with sunlight — otherwise some places wouldn’t see the sun come up until almost 8:30 a.m.
又到了每年的這個時候。儘管你發誓將鬧鐘設為上午7點，你醒來並看到廚房的時鐘是上午8點。你確信你工作遲到了。
可是等等，你們也沒有遲到。 這是日光節約時間。
一年兩次，世界各地的時鐘向前或向後移動一個小時。
但這代表者甚麼呢？
有一個古老的神話，即“日光節約時間”是一種習慣，可以使農民在陽光下有更多的時間在田野裡工作。但是，這並不是有幾十個國家遵循它的原因。
夏令時間（DST）是一種通過延長早上的時間來減少用電量的系統。在一年中的八個月中，美國和其他數十個國家/地區都按照夏令時進行調整，在剩下的四個月中將恢復到標準時間以充分利用有陽光的時間。
3月的第二個星期日凌晨2點，時鐘向前移動一小時。然後，在11月的第一個星期日凌晨2點，時鐘將倒轉一個小時。要能夠記住這變化的好方法是，時間的變化與季節相吻合：3月的時鐘“跳躍”(春天)前進一個小時，11月的時鐘“往後”(秋天)。
在夏季的月份，太陽會長出現比久，因此你可以靠著日光節省打開燈光的時間。冬季的月份將會倒回為標準時間，這樣太陽提早升起的時候就可以照亮人們一天的開始。否則，有些地方要到早上8:30才會看到太陽升起。
When did it start?
The current March-November system the US follows began in 2007, but the concept of “saving daylight” is much older. It’s debated who originally *came up with the idea, but Benjamin Franklin *appeared to have first mentioned it in 1784, when he wrote a letter to the editor of the Journal of Paris.
DST wasn’t widely used until more than a century later, though. Several countries, including Britain and Germany, *implemented DST during World War I. The practice aimed to cut *artificial lighting use so troops could *conserve fuel for the war. But the US didn’t standardize the system until 1966, when it passed the Uniform Time Act.
For years, the US observed DST from the first Sunday of April to the last Sunday of October. In 2005, President George W. Bush extended DST an extra four weeks, officially taking effect in 2007.
But not everyone has opted to follow DST. Only 70 countries around the world “save daylight” every year. In the US, states are not required by law to follow DST — Hawaii and most of Arizona do not observe it. Other states — like Florida and California — are working to observe DST year-round (rather than just between March and November).
它何時開始？
美國目前採用的3月至11月的系統始於2007年，但是“節省日光”的這個概念其實已經很久了。這樣有爭議性的論點其實在早在最初就提出了，但本傑明·富蘭克林似乎在1784年寫信給巴黎日誌的主編時，就首次提到了這個主意。
但是，直到一個多世紀之後，DST才被廣泛使用。第一次世界大戰期間，包括英國和德國在內的幾個國家實施了DST。主要用意是在減少人工照明的使用，以便部隊可以節省戰爭的燃料。但是美國直到1966年通過《統一時間法》才使該系統標準化。
這麼多年來，美國從4月的第一個星期日到10月的最後一個星期日都遵守DST。 2005年，布什總統將夏令時延長了四個星期，並於2007年正式生效。
但是，並非所有人都選擇遵循DST。全世界每年只有70個國家“節省日光”。在美國，法律不要求各州遵守夏令時（DST），夏威夷和亞利桑那州的大部分地區未遵守夏令時。其他州-例如佛羅里達州和加利福尼亞州-正在努力全年觀察夏令時（而不是僅僅在三月到十一月之間）。
Does DST actually work?
Well … It’s debated.
While the practice can help reduce some energy *consumption, critics have raised concerns of whether the amount of energy saved is worth the *hassle of implementing the system around the world.
In 2008, the US Department of Energy found that the four-week extension of DST from April-October to March-November saved about 0.5 percent in total electricity every day. While that seems like almost nothing, it totals 1.3 billion kilowatt-hours and the DOE says that adds up to “the amount of electricity used by more than 100,000 households for an entire year.”
But a study that same year by the National Bureau of Economic Research concluded that DST increases the demand for electricity — even though lighting usage reduced, demand for heating and cooling increased, so electricity *consumption was about the same.
Other studies have found that benefits of DST may be location-specific. One found electricity reductions in Norway and Sweden, while another saw increased electricity demand in Indiana.
Whether or not “saving daylight” is the most energy efficient method for electricity conservation is still up for debate. But for now, if you live in any of the countries that follow DST, remember to switch your clocks back before you go to sleep Sunday night. Otherwise you’ll wake up thinking you’re late to work.
日光節約時間真的有效嗎？
好吧…這是可以有議論的空間。
儘管這種做法可以幫助減少一些能源消耗，但批評者對節省的能源是否值得在世界範圍內實施該系統感到煩惱。
2008年，美國能源部發現DST從4月至10月延長到3月至11月期間的4個星期，每天可節省約0.5％的總電量。儘管這似乎看起來沒甚麼影響，但它總計為13億千瓦時，能源部說這合計為“整年超過100,000戶家庭的用電量”。
但是，同年美國國家經濟研究局（National Bureau of Economic Research）進行的一項研究得出的結論是，日光節約時間使電力需求增加了-儘管減少了照明使用，對暖氣和冷氣的需求卻增加了，所以耗電量大致相同。
其他研究發現，DST的好處可能是針對特定位置的。其中一個研究發現挪威和瑞典的電力減少，而另一個發現印第安納州的電力需求增加。
“節約日光”是否是最節能的節電方法仍有待商確。但是現在，如果您居住在DST之後的任何國家/地區，請記住在周日晚上睡覺之前將時鐘切換回原來的狀態。否則，你會以為自己遲到了而醒過來。
