Daylight Saving Time 101: What You Need to Know

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Article at a Glance: 

  • Every year, people all over the world change their clocks (spring forward one hour in spring, fall back one hour in fall) in accordance with Daylight Saving Time. 
  • This practice has a lengthy history dating back to the days of Benjamin Franklin, who believed that more daylight would help reduce the demand for lights and electricity, and therefore save money. 
  • Chronobiologists have found the Daylight Saving Time can cause circadian rhythm disruption and negatively impact human healthy.
  • Other stakeholders who oppose Daylight Saving Time argue that there are negative implications on scheduling — especially for agricultural workers and religious groups.
  • Not all states or countries celebrate Daylight Saving Time, which means that part of the world is out of sync with the other for a large part of the year.

  1. The observance of Daylight Saving Time (DST) is over 100 years old!
    While some ancient civilizations employed shortened and lengthened calendar days depending on the season, it wasn’t until the 20th century that DST became widely recognized.

    At the time, Europe was facing coal shortages and blackouts. Germany was the first country to embrace DST in the effort to conserve fuel and cut industrial costs during World War I.


  2. Despite popular belief, DST was not created to benefit farmers.
    The common myth is that DST was created for the agriculture industry and supported by farmers because it would allow for extended daylight hours to work in the field.  The truth of the matter is that farmers were largely opposed to the idea of shifting the clocks because doing so would disrupt their methodically orchestrated schedule.  For example, it’s very difficult to explain to farm animals (like dairy cows) why they are being milked later or earlier than normal, depending on the season. Farmers have to stay on a regimented schedule with the buyers they are selling produce and milk to so that they can profit from their labor.  DST tends to complicate production for both farmers and the animals; in general, it makes more sense to most farmers if they rely on the sun and the seasons to determine things like milking times and the best time to harvest crops.


  3. For decades, the United States was known as “a chaos of clocks.”
    For many years, states and cities throughout the nation had varying start and end dates for DST.  This meant that you could travel throughout a single state and experience numerous time changes by the time you reached your destination.  The Uniform Time Act of 1966 finally brought some order by establishing a standardized DST start and end date across the nation.  It started from the last Sunday in April and continued until the last Sunday in October.


  4. Two U.S. states and a handful of other U.S. territories still don’t participate in DST.
    Under the Uniform Time Act of 1966, states had the option of remaining on standard time year-round if they want to.  Today, there are two states that notably do not participate in DST.

    Most of Arizona — with the exception of the state’s Navajo Nation — hasn’t observed DST since 1968, primarily because this part of the country gets long hours of daylight and warmer temperature throughout the entire year.  Hawaii opted out of the Uniform Time Act because of its proximity to the equator. Given its location, the sun rises and sets at approximately the same times every day, no matter the season.  Several U.S. territories – including the U.S. Virgin Islands, Puerto Rico, Guam, and American Samoa – also don’t observe DST for essentially the same reasons as Hawaii.


  5. 26 U.S. states are considering make DST a year-round affair. Florida could be the first to do so.
    According to the Department of Transportation, the body in charge of time zones within the U.S., a state can not “permanently” stay on daylight saving time under today’s federal law.  However, U.S. Senator Marco Rubio, of Florida, is pushing hard to get the Sunshine Protection Act passed by Congress.  If approved, Florida could be the first state to remain an hour ahead of the rest of the East Coast during the winter months.


  6. Rule of thumb: DST is not typically observed as you move closer to the equator.
    Since the sun naturally rises and sets around the same time every day along the equator, DST simply isn’t necessary at this latitude.


  7. DST probably doesn’t yield energy savings worth stressing over.
    During the summer months, when there are longer hours of sunlight, your lighting and electricity consumption may go down slightly. But many studies show that this is effectively outweighed by the increase in air conditioning consumption.  And in the winter, your heat and gas consumption also typically increase. So in the end, your energy/cost savings is a wash.


  8. DST can have unforeseen health effects.
    According to Dr. Matthew Walker, (Professor of Neuroscience at UC Berkeley, Sleep Scientist at Google, and  Author of Why We Sleep), shifting the clock forwards and backwards during the year does have a direct impact on the human body and its ability to function properly.

    “In the spring, when we lose one hour of sleep, we see a subsequent 24% increase in heart attacks. In the fall, when we gain an hour of sleep, we see a 21% decrease in heart attacks. That’s how fragile your body is to even just the smallest changes in your hours of sleep.” – Professor Walker

    Research has also shown that the sleep deprivation people experience – when DST begins in the Spring and ends in the Fall – results in an increase of fatal accidents. More specifically, when people lose an hour of sleep in the Spring, they are driving while tired and are more likely to get into an accident. In the Fall, people tend to take advantage of having an extra hour available to them; it’s not uncommon to stay out later into the night and/or engage in drinking alcohol — both of which can contribute to a greater likelihood of getting into an accident.

    *This is one of the many reasons why we are so passionate about helping people take more control of the light in their environment — so that they can also get better sleep at night. Read: This is Your Brain on TrueDark® Twilights Glasses.


  9. The correct spelling for this observance is “daylight saving time”, without the extra “s”.
    It’s not uncommon to hear someone say that it’s “daylight savings time”, but the correct way to say it is in fact without the extra “s” after “saving”.  For extra grammatical points, the name should also be written in all lowercase letters when used in the middle of a sentence. This observed period is also known in parts of the world (like the UK) as “summer time”.


  10. It’s common practice to change the batteries in the smoke alarm detectors throughout your home when daylight saving time ends.
    While you’re doing so, don’t forget to cover up the light on the detector itself (because it’s typically green or blue, which can impact your sleep!). You can use TrueDark® Dots to cover up these tiny beams of light and #stopjunklight throughout other areas of your home.
    Read: 5 Easy Ways to Stop Junk Light at Home


  11. ½  Legally, bars across the U.S. do have the option to stay open for an extra hour once a year thanks to DST’s end date.
    This does not mean that you should not exercise caution in staying out later than normal and driving, especially while under the influence. Please refer back to #7 in this list!

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