How Many Minutes of Daylight Do We Gain Each Day? And Other Daylight Saving Time Facts

By Helen LinLast Updated Feb 24, 2021 7:53:54 PM ET
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Nearly everyone in the United States is familiar with Daylight Saving Time (DST), but if you're not, you'll learn everything there is to know about DST in this article. Twice a year, most Americans wake up after losing an hour of snooze time in early spring (or late winter) — or gaining an hour of sleep in late autumn. And that’s kind of all we know about it: It impacts our sleep habits and, in part, regulates how much of the sun we’ll be seeing during business hours.

In 2021, states that observe DST will be "springing ahead" an hour on Sunday, March 14, which is when we enter DST, and "falling back" an hour on Sunday, November 7, which is when DST ends. Without a doubt, Daylight Saving Time plays a considerable role in our everyday lives. So, where did the idea come from, and why was it implemented? And, perhaps most importantly, why does it still exist? Let’s explore the logic behind the century-old practice.

History and Purpose of Daylight Saving Time

Some people give Benjamin Franklin credit for the idea because of an essay he penned in 1784. Others claim either Canada or Germany established Daylight Saving Time in the early 1900s. Regardless, during World War I, the United States government needed a way to increase production while saving energy, and Daylight Saving Time, which takes advantage of the later hours of sunlight from April through October, seemed like a great solution. When the U.S. joined the war effort during World War II, the federal government required states to observe Daylight Saving Time.

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Following World War II, the federal government afforded states the option of observing Daylight Saving Time. By 1966, Congress passed the Uniform Time Act, which standardized the length of Daylight Saving Time. Due to the Energy Policy Act's passage in 2005, Daylight Saving Time was extended four weeks, lasting from the second Sunday in March through the first Sunday in November.

As stated, the idea behind Daylight Saving Time is to save energy. With this in mind, Congress signed the Energy Policy Act into law to save 10,000 barrels of oil each day. Lawmakers predicted a reduction in oil consumption by reducing the power utilized by businesses during the daylight hours. Unfortunately, it is nearly impossible to quantify the amount of energy savings, if there is any at all. Regardless of fossil fuel energy savings, Daylight Saving Time continues throughout most of the United States.

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How Daylight Saving Time Works

Daylight Saving Time begins on the second Sunday in March at 2:00 am, when we set our clocks forward to 3:00 am. This also means we effectively lose an extra hour of sunshine until Daylight Saving Time ends on the first Sunday in November at 2:00 am, when we turn our clocks back to 1:00 am. The popular mnemonic device for remembering how to adjust the clocks on those days is "spring forward, fall back."

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As the sun moves higher in the sky between March and June, there are two more minutes of daylight each day. Also, the higher someone’s latitude and further distance from the equator, the longer the sun remains above the horizon. In August, the daylight loss rate accelerates by two minutes each day until the winter solstice between December 20 and 23. At this time, the North Pole sits farthest from the sun, becoming the shortest day of the year. On June 21, the Northern Hemisphere is closest to the sun, making it the hottest and longest day of the year.

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From the vernal equinox in March through the summer solstice in June, the daylight exposure in the Northern Hemisphere increases. Hence why people in Australia experience winter during what is summer north of the equator. This, of course, figures in to when (and why) the U.S. observes DST.

Where Is Daylight Saving Time Recognized?

Forty-eight states currently observe Daylight Saving Time. Arizona opted out of the practice in 1968 due to the excessive heat during the summer months. According to NASA, the Navajo Nation in Northeastern Arizona observes DST.

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Hawai’i never observed Daylight Saving Time under the Uniform Time Act due to its tropical latitude. The state legislature briefly enacted Daylight Saving in 1933. However, the state repealed the law within three weeks. Additionally, the weather in Hawai’i rarely fluctuates, so Daylight Saving had virtually no effect on energy consumption.

The topic of Daylight Saving Time seems to resurface with each election cycle. In 2020, Florida Senators Marco Rubio and Rick Scott introduced the Sunshine Protection Act — a modern example of how Daylight Saving Time remains an essential topic of political and scientific conversation. Meanwhile, the European Union voted to eliminate biannual time changes in 2019. Several U.S. states are also considering similar laws due to the health risks.

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Daylight Saving Time and Human Health

One universal complaint about Daylight Saving Time is that we "lose an hour" of sleep. Joseph S. Takahashi, Ph.D., Chair of the Department of Neuroscience at UT Southwestern, studied the effects of desynchronization on the human body. UT Southwestern Medical Center says, "this twice-a-year desynchronization of our body clocks has been linked to increased health risks such as depression, obesity, heart attack, cancer, and even car accidents."

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Every cell in the human body keeps track of time. Changes to daily routines lead to sleep deprivation, memory loss, difficulty learning, and cognitive function. In 1997, Dr. Takahashi’s lab discovered the CLOCK gene, "the first circadian gene in mammals." Mutated CLOCK genes may cause delays in circadian functions "leading to dysfunctions in metabolic, behavioral, and cognitive abilities."

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By 2016, Dr. Takahashi’s laboratory discovered the first genes in mice that regulate sleep. The study turned up "two genes in mice that control how much rapid eye movement (REM) sleep and non-REM sleep is needed." Healthy sleep patterns rely on lengthy non-REM sleep moments while the brain is not dreaming and processing memories. The findings suggest methods for improving sleep hygiene for the nearly 20% of the population who suffer from sleeping disorders. Therefore, Daylight Saving Time, and other external factors from the environment, play a considerable role in disrupting human health.