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Daylight Saving Time. Why do we change the clocks?

The tradition of moving clocks forward during the summer months is known around the globe as Daylight Saving Time (DST). With the arrival of spring, people set the clocks one hour forward from the standard time. Although this practice is peculiar to the majority of the western countries, not all regions and states accept DST.

dst clocks

This concept has various implications for the population, including negative and positive outcomes. The primary purpose of DST is to increase the effectiveness of people during the sunlight. However, with the advancement of technologies and shifts in the lifestyle of the world population, this tradition became less relevant and more of a controversial issue.

DST became a significant part of people's life who follows this tradition. Nevertheless, it has negative effects on the health of people as well as creates complications for international communication.

Around the globe, people set clocks one hour forward on the last Sunday of March. Nevertheless, in the United States, DST starts on the second Sunday of March. Also, the time when the shift occurs differs from country to country. Some regions forward the clocks in the middle of the night at 01:00 a.m. or 02:00 a.m. local time1. This practice signifies the arrival of the spring and lasts till the Autumn. Meanwhile, the return to the standard time takes place in October or November.

summer time

Rules in the United States

In the United States, the rules of the DST require setting clocks one hour forward on the second Sunday of March at 02:00 a.m. The people return to the standard time on the first Sunday of November. Besides, the rules for DST have been subject to changes according to the area. The last time Congress made the amendment to DST was 2007. These changes to the Energy Policy Act were aimed to extend the period of DST to reduce energy consumption by the population2.

Winter time

The return from DST is associated with the term “winter time”. This concept is mainly used in Europe and countries which do not follow DST. In particular, the population and politicians tend to call the standard time as “winter time”, while the period during DST is called “summer time”. Thus, the terms “winter time” and “summer time” are only the denomination of standard time and Daylight Saving Time (DST).

DST time changes

The history of DST

The concept of increasing daylight time has been relevant since the ancient civilizations. Namely, the Romans employed different types of time measures to increase the activities during the most productive hours of daylight3. Unlike modern people, ancient civilizations were more flexible and could easily switch to the required time.

Eventually, the more developed idea to maximize the efficiency of people during the daylight was proposed by Benjamin Franklin. Later, the influential politician Winston Churchill also advocated implementing this concept. It would allow people to be more productive during the daylight and could be an effective decision to save energy.

First implementations on the national level

During the First World War, in 1916, Kaiser Wilhelm was the first leader who decided to enable DST because he recognized that increasing the hours of daylight nationwide would benefit the energy consumption and health of people and soldiers in particular4.

After Germany, many other European adopted the Daylight Saving Time due to its perceived benefits for the population and energy efficiency.

The United States joined the format of DST

Along with the adoption of the Standard Time Act of March 19, 1919, in the United States, the first time DST was implemented was at 02:00 a.m on March 31 in the same year. On this day, people were asked to stop their clocks for one hour. The return to the standard time was scheduled in seven months5.

However, following the World War, this practice was criticized by the population and politicians of the United States. Although DST became optional for the areas, the major part of the country proceeded to use it till today. Only several areas decided to opt out from DST because it was not suitable due to the climate conditions.

DST around the world

Considering that DST is the widely applicable practice in the world, some countries developed own rules and terminology for this occurrence. In particular, the countries which do not follow DST live in the Winter Time Zones (Standard Time Zone). Among the most popular countries which do not observe DSTare the following:

  • China
  • Japan
  • Russia
  • The United Arab Emirates
  • North Korea
  • South Korea
  • Argentina
  • Most recently Brazil (since 2019)

How DST affects energy consumption in the world

The change of the clocks to the Daylight Saving Time is frequently associated with shifts in the life of people and international communication. Even though one of the initial goals of this practice was to save energy, in the contemporary world, the results are ambiguous. The efficiency of the DST in the conservation of energy has been doubted because contemporary households rely on air conditioning. As a result, with the increase of the daylight hours, people use conditioning systems more frequently which consume a greater amount of electricity than house lightning. Hence, the countries which studied the electricity bills during the DST reported that energy had been increased6.

Advantages and disadvantages of DST

The central question of the DST remains to be its effectiveness for the population. Despite the contemporary criticism of this practice, the implementation of DST has the following pros:

  • More daylight increases the Vitamin D synthesis
  • People have more time for exercises and other tasks during the day
  • More frequent exposure to sunlight positively affects the mood and decrease the depressive conditions7
  • The retail businesses benefit from the more customers who visit the shops during the late daylight hours
  • Drivers do not drive in the dark, thus decreasing the risks of traffic accidents

Nevertheless, there are also drawbacks from switching clocks one hour forward. Namely, the cons of DST are:

  • Affects the productivity of people
  • Disrupts the sleeping habits
  • Increased tiredness from the changes in biorhythm
  • Affects the seasonal adaptation and sleep-wake cycle of the weather-sensitive individuals8
  • Electricity use of air conditioning increases. Subsequently, it contributes the global warming.

These lists demonstrate that the primary benefits of the DST involve more daylight for the leisure of people, while the drawbacks are related to the consequences of the sudden shift in the time.

DST in Europe

With the historical adoption of DST in Germany, other countries recognized the positive effects of this practice. In particular, it was evident that people would benefit from the extra hour of daylight while using less energy. As a result, the majority of the European countries adopted DST as the annual tradition.


The decision to start using DST among the state members of the European Union was impacted by the European Commission which issued the directives on how to implement it. In 1981, the Commission along with the European Economic and Social Committee started the regulation and provided suggestions regarding the positive effects of DST9.

Subsequently, these legislative bodies constantly study the effectiveness of this practice and how it benefits the citizens. Also, the organizations collect the data from the studies and public opinion to determine whether any amendments to DST are needed.

Public opinion on DST

Since the adoption of DST, many people have expressed their concerns regarding the implications of sudden changes in the biorhythm. Since citizens and members of parliament reconsidered their attitudes towards DST and asked to make changes, multiple public hearings were organized.

The most important hearing was organized in 2015 with a discussion on how to rework summer time or cancel it altogether. Moreover, the citizens criticize DST and appeal to the EU summertime agreements. As a result, the European Parliament often receives public petitions on this subject with the proposition to change the procedures of DST.

DST in the United States

The population and scientists express criticism concerning the effectiveness of DST in the United States. In particular, the primary argument remains to be the fact that the benefits of increasing daylight were relevant only during times of low technological development. Energy conservation is no longer effective with the increase of daylight hours.


The shifts of the clocks affect the dairy farmers because it is difficult for cows to change the biorhythm. As a result, this issue negatively contributes to their ability to produce milk. Subsequently, DST is considered to have a negative impact not only on the human sleep cycle but also on the productivity of agriculture.

The critics emphasize that electricity conservation is actually worse or not noticeable during DST. For example, the study in Indiana state indicated the greater use of air-conditioning systems10. Therefore, the gain from the lighting savings is lower than the losses from the functioning of other appliances.

Which states do not observe DST

Although the United States accepted the use of DST for the country, there are several exceptions. Namely, Hawaii decided not to implement DST due to the notion that during the year, the daily sunlight cycle is the same. Similarly, the U.S territories like the Virgin Islands, Puerto Rico, Guam, and American Samoa also do not require DST due to the same reasons. In this regard, one may admit that the areas which are located near the equator do not benefit from the extra hour of daylight.

Nevertheless, the state of Arizona has unique attitudes towards DST. The state decided not to follow the tradition of daylight saving and yet the Navajo Reservation which is located on the territory of the state does set clocks one hour forward. Considering the climate and extremely hot temperature during the summer months, the additional hour of daylight is more damaging than effective for the population of Arizona. Therefore, the residents of the state actually would appreciate even fewer daylight hours during the hot months.

The impact of DST


Since the implementation of DST, many researchers have tried to identify the effects of daylight saving on the health of people. However, only in the modern world, medical institutions managed to study the impact of this practice on the functioning of the body. The shift to DST is associated not only with sleep deprivation and increased tiredness but also with the negative implication for a brain and heart. The studies report that shift to DST correlates with the risks of following health issues:

  • Heart attack
  • Ischemic stroke
  • Cardiovascular disease
  • Sleep deprivation11

Along with the disruption in the biorhythm of a person, DST might have severe implications for the people.

Daily life

The most obvious impact of DST on daily life is the change in the daily routine and leisure activities. With more daylight hours, people are willing to go to parks, shopping, or restaurants. In addition, people have more time to engage in outdoor sports activities that require sunlight. In this regard, the population has extra time for recreation after work. The experts also indicate that people are more productive during the evening daylight rather than in the morning time. In this regard, the extra daylight gives more opportunities for recreation and personal activities.


The influence of DST on the economy is much more subtle and can be invisible to the general population. However, on a small scale, DST affects international business and trade. For instance, the shift in the communications between the countries, jet lag from the business trips, and operation of the logistics contribute to the low delays in the work. As a result, the research shows that the shift in the clocks negatively influences the performance of the international business12. Similarly, the decreased performance of the employees might affect the economy of a country.

Future of DST

The ambiguity and uncertain benefits of DST influenced the world to reconsider this practice. Nowadays, with the development of technologies and studies that prove the negative effects, leaders started to doubt that the general concept of switching clocks is relevant in the contemporary world.

Plans to cancel DST

The European Parliament proposed to shift permanently to either summer or winter time. The legislation implies that by 2021, the countries of the European Union could decide what time standard they will use. The states which decided to permanently use summer time would move the clocks one hour forward for last time on the last Sunday of March 2021. The survey indicates that the majority of votes would be in favor of switching to one of the time standards.

Along with Europe, Canada also wants to abandon the concept of DST due to its implications for health, public safety, and energy consumption. The province of British Columbia passed legislation to establish daylight time permanently. Besides, all provinces in Canada and the 26 states in the United States work on abandoning this practice because the shifts in the biorhythms of a person twice a year have adverse effects on the well-being of the population.

Is it here to stay?

Undoubtedly, the criticism towards DST and its effectiveness require the nations to reconsider this practice. Mainly because the sudden shifts in the sleeping cycle affect people’s health. One of the most popular propositions remains to be the permanent shift to one of the time standards. However, different regions have own reasons to either scrap or proceed following DST. The local authorities have to determine whether the benefits for the people outweigh the cons of DST.

For the population, the increase of daylight hours could be the significant advantage to devote more time to recreational and sports activities. Meanwhile, the transition to DST triggers sleep-related issues and negatively impact the performance of the employees. Consequently, one may agree that DST is applicable only in certain areas considering the climate and geography of a country.


  1. All Timezones with DST”, worlddata.info
  2. Daylight Saving Time Rules”, nist.gov
  3. Berthold (1918). "Daylight saving in ancient Rome". The Classical Journal. 13 (6): 450–451.
  4. David S. Prerau (2005). “Saving the Daylight: Why We Put the Clocks Forward”, Granta Books. ISBN 978-1862077966
  5. Clocks Change Tomorrow” (1918), The New York Times
  6. Does Daylight Saving Time Conserve Energy?”, scientificamerican.com
  7. Average sunrise time predicts depression prevalence, Henry Olders (2003), Journal of Psychosomatic Research, 55 (2): 99–105
  8. Pablo Valdez; Candelaria Ramírez; Aída García (2003). "Adjustment of the sleep–wake cycle to small (1–2h) changes in schedule". Biological Rhythm Research. 34 (2): 145–155.
  9. Communication from the commission to the Council, the European Parliament and the European economic and social committee under Article 5 of Directive 2000/84/EC on summer time arrangements”, European Commission. 23 November 2007
  10. Time to Move On? The Case Against Daylight Saving Time”, nationalgeographic.com
  11. Beth A. Malow; Olivia J. Veatch; Kanika Bagai (2019). “Are Daylight Saving Time Changes Bad for the Brain?” JAMA Neurol, 2020;77(1):9-10
  12. Study Reveals Impact of Time Differences on International Trade”, uea.ac.uk
  • When do we change the clocks in spring?

    In the United States, people switch clocks one hour forward on the second Sunday of March. Around the world, DST occurs during the last weekend of March.

  • Clocks forward or back?

    The rules of Daylight Saving Time (DST) imply moving clocks one hour forward in spring and return to the Standard Time (1 hour back) in fall.

  • Why we change the clocks?

    Daylight Saving Time was introduced to provide an extra hour of daylight to conserve energy and maximize sunlight time for outdoor activities of people.

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