Daylight saving time (DST) is the practice of advancing clocks during warmer months so that darkness falls later each day according to the clock.
Proponents of DST generally argue that it saves energy, promotes outdoor leisure activity in the evening (in summer), and is therefore good for physical and psychological health, reduces traffic accidents, reduces crime or is good for business.[ citation needed ]
Opponents argue that DST disrupts human circadian rhythms (negatively impacting human health in the process), [1] [2] that it increases fatal traffic collisions, [3] that the actual energy savings are inconclusive, [4] and that DST increases health risks such as heart attack. [4] Farmers have tended to oppose DST. [5] [6]
Having a common agreement about the day's layout or schedule has so many advantages that a standard schedule over whole countries or large areas has generally been chosen over efforts in which some people get up earlier and others do not. [7] The advantages of coordination are so great that many people ignore whether DST is in effect by altering their work schedules to coordinate with television broadcasts or daylight. [8] DST is commonly not observed during most of winter, because the days are shorter then; workers may have no sunlit leisure time, and students may need to leave for school in the dark. [9] Since DST is applied to many varying communities, its effects may be very different depending on their culture, light levels, geography, and climate. Because of this variation, it is hard to make generalized conclusions about the effects of the practice. The costs and benefits may differ between places. Some areas may adopt DST simply as a matter of coordination with other areas rather than for any other benefits.
A 2017 meta-analysis of 44 studies found that DST leads to electricity savings of 0.3% during the days when DST applies. [10] [11] The meta-analysis furthermore found that "electricity savings are larger for countries farther away from the equator, while subtropical regions consume more electricity because of DST." [10] [11] This means that DST may conserve electricity in some countries, such as Canada and the United Kingdom, but be wasteful in other places, such as Mexico, the southern United States, and northern Africa. The savings in electricity may also be offset by extra use of other types of energy, such as heating fuel.
The period of daylight saving time before the longest day is shorter than the period after, in several countries including the United States of America, in areas that observe daylight saving time, and Europe. For example, in the U.S. the period of daylight saving time is defined by the Energy Policy Act of 2005. The period for daylight saving time was extended by changing the start date from the first Sunday of April to the second Sunday of March and changing the end date from the last Sunday in October to the first Sunday in November.
DST's potential to save energy comes primarily from its effects on residential lighting, which consumes about 3.5% of electricity in the United States and Canada. [12] (For comparison, air conditioning uses 16.5% of energy in the United States. [13] ) Delaying the nominal time of sunset and sunrise reduces the use of artificial light in the evening and increases it in the morning. However, approaching extreme latitudes, even with DST, the days are long enough that most people wake up after sunrise. An early goal of DST was to reduce evening usage of incandescent lighting, once a primary use of electricity. [14] Although energy conservation remains an important goal, [15] energy usage patterns have greatly changed since then. Electricity use is greatly affected by geography, climate, and economics, so the results of a study conducted in one place may not be relevant to another country or climate. [12]
Several studies have suggested that DST increases motor fuel consumption. [12] The 2008 DOE report found no significant increase in motor gasoline consumption due to the 2007 United States extension of DST. [26]
Those who benefit most from DST are the retailers, sporting goods makers, and other businesses that benefit from extra afternoon sunlight. [16] Having more hours of sunlight in between the end of the typical workday and bedtime induces customers to shop and to participate in outdoor afternoon sports. [27] People are more likely to stop by a store on their way home from work if the sun is still up. [16] In 1984, Fortune magazine estimated that a seven-week extension of DST would yield an additional $30 million for 7-Eleven stores, and the National Golf Foundation estimated the extension would increase golf industry revenues $200 million to $300 million. [28] A 1999 study estimated that DST increases the revenue of the European Union's leisure sector by about 3%. [12]
Conversely, DST can harm some farmers, [4] [29] and others whose hours are set by the sun. [30] One reason why farmers oppose DST is that grain is best harvested after dew evaporates, so when field hands arrive and leave earlier in summer, their labor is less valuable. [31] Dairy farmers are another group who complain of the change. Their cows are sensitive to the timing of milking, so delivering milk earlier disrupts their systems. [6] [32] Today some farmers' groups are in favor of DST. [33]
Children and teenagers often have difficulty getting enough sleep at night when the evenings are bright. [4]
DST also hurts prime-time television broadcast ratings, [34] [4] drive-ins and other theaters. [35]
Changing clocks and DST rules has a direct economic cost, entailing extra work to support remote meetings, computer applications and the like. For example, a 2007 North American rule change cost an estimated $500 million to $1 billion, [36] and Utah State University economist William F. Shughart II has estimated the lost opportunity cost at around US$1.7 billion. [4] Although it has been argued that clock shifts correlate with decreased economic efficiency, and that in 2000 the daylight-saving effect implied an estimated one-day loss of $31 billion on U.S. stock exchanges, [37] the estimated numbers depend on the methodology. [38] The results have been disputed, [39] and the original authors have refuted the points raised by disputers. [40]
In 1975 the United States Department of Transportation (DOT) conservatively identified a 0.7% reduction in traffic fatalities during DST, and estimated the real reduction at 1.5% to 2.0%, [41] but the 1976 NBS review of the DOT study found no differences in traffic fatalities. [9] In 1995 the Insurance Institute for Highway Safety estimated a reduction of 1.2%, including a 5.0% reduction in crashes fatal to pedestrians. [42] Others have found similar reductions. [43] Single/Double Summer Time (SDST), a variant where clocks are one hour ahead of the sun in winter and two in summer, has been projected to reduce traffic fatalities by 3% to 4% in the UK, compared to ordinary DST. [44] However, accidents do increase by as much as 11% during the two weeks that follow the end of British Summer Time. [45] Likewise in the United States, vehicular collisions with deer increase, purportedly by 16%, in the week after the end of Daylight Saving Time. [46] It is not clear whether sleep disruption contributes to fatal accidents immediately after the spring clock shifts. [47] A correlation between clock shifts and traffic accidents has been observed in North America and the UK but not in Finland or Sweden. Four reports have found that this effect is smaller than the overall reduction in traffic fatalities. [48] [49] [50] [51] In 2022, a driving simulator study documented a significant worsening of several driving performance indicators in the week after the spring transition to DST. [52] A 2009 U.S. study found that on Mondays after the switch to DST, workers sleep an average of 40 minutes less, and are injured at work more often and more severely. [53]
DST likely reduces some kinds of crime, such as robbery and sexual assault, as fewer potential victims are outdoors after dusk. [54] [17] Artificial outdoor lighting has a marginal and sometimes even contradictory influence on crime and fear of crime. [55]
In several countries, fire safety officials encourage citizens to use the two annual clock shifts as reminders to replace batteries in smoke and carbon monoxide detectors, particularly in autumn, just before the heating and candle season causes an increase in home fires. Similar twice-yearly tasks include reviewing and practicing fire escape and family disaster plans, inspecting vehicle lights, checking storage areas for hazardous materials, reprogramming thermostats, and seasonal vaccinations. [56] Locations without DST can instead use the first days of spring and autumn as reminders. [57]
A 2017 study in the American Economic Journal: Applied Economics estimated that "the transition into DST caused over 30 deaths at a social cost of $275 million annually," primarily by increasing sleep deprivation. [58]
Using a large US database of 732,835 fatal motor vehicle accidents (MVA) recorded from 1996 to 2017, Fritz et al. (2019) found a 6% increase in fatal MVA risk in the workweek following the spring transition to DST, which was more pronounced in the morning and the further location west within a time zone. There were no effects of the fall-back transition to standard time (ST) on MVA risk, supporting the hypothesis that circadian misalignment and sleep deprivation underlie MVA risk increases. [59]
In March 2020, the Israeli government planned to delay daylight saving in order to discourage gatherings during the COVID-19 pandemic. However, it was decided this would be too technically difficult to implement at such short notice. [60]
Experts in circadian rhythms and sleep have warned about the negative health implications of DST. DST reduces sleep time and causes an increased mismatch between the body clock and local time, a condition called social jetlag. Both sleep deprivation and social jetlag have been associated with negative effects on physical and mental health outcomes, including increased risks for diabetes, obesity, heart disease, depression, and some forms of cancer. [1] [2] [62] Year-round standard time has been proposed as the preferred option for public health and safety. [63] [64] [65] [66] [67]
In societies with fixed work schedules DST provides more afternoon sunlight for outdoor exercise. [68] It alters sunlight exposure depending on one's location and daily schedule, as sunlight triggers vitamin D synthesis in the skin, but overexposure can lead to skin cancer. [69] DST may help in depression by causing individuals to rise earlier, [70] but some argue the reverse. [71] The Retinitis Pigmentosa Foundation Fighting Blindness, chaired by blind sports magnate Gordon Gund, successfully lobbied in 1985 and 2005 for U.S. DST extensions. [72] [73] DST shifts are associated with higher rates of ischemic stroke in the first two days after the shift, though not in the week thereafter. [74]
Clock shifts were found to increase the risk of heart attack by 10 percent, [4] and to disrupt sleep and reduce its efficiency. [75] Effects on seasonal adaptation of the circadian rhythm can be severe and last for weeks. [76] A 2008 study found that although male suicide rates rise in the weeks after the spring transition, the relationship weakened greatly after adjusting for season. [77] A 2008 Swedish study found that heart attacks were significantly more common the first three weekdays after the spring transition, and significantly less common the first weekday after the autumn transition. [78] A 2013 review found little evidence that people slept more on the night after the fall DST shift, even though it is often described as allowing people to sleep for an hour longer than normal. The same review stated that the lost hour of sleep resulting from the spring shift appears to result in sleep loss for at least a week afterward. [79] Even so, a 2014 study conducted in the United States showed that heart attacks decreased significantly after the fall DST shift. [80]
The government of Kazakhstan cited health complications due to clock shifts as a reason for abolishing DST in 2005. [81] In March 2011, Dmitri Medvedev, president of Russia, claimed that "stress of changing clocks" was the motivation for Russia to stay in DST all year long. Officials at the time talked about an annual increase in suicides. [82]
An unexpected adverse effect of daylight saving time may lie in the fact that an extra part of morning rush hour traffic occurs before dawn and traffic emissions then cause higher air pollution than during daylight hours. [83]
In 2017, researchers at the University of Washington and the University of Virginia reported that judges who experienced sleep deprivation as a result of DST tended to issue longer sentences. [84]
DST's clock shifts have the obvious disadvantage of complexity. People must remember to change their clocks; this can be time-consuming, particularly for mechanical clocks that cannot be moved backward safely. [85] People who work across time zone boundaries need to keep track of multiple DST rules, as not all locations observe DST or observe it the same way. The length of the calendar day becomes variable; it is no longer always 24 hours. Disruption to meetings, travel, broadcasts, billing systems, and records management is common, and can be expensive. [86] During an autumn transition from 02:00 to 01:00, a clock reads times from 01:00:00 through 01:59:59 twice, possibly leading to confusion. [87]
Lists of time zones and time differences usually do not include daylight saving time, as that is considered complicated and would mean different times over the seasons of the year. For example, UK is usually listed as UTC±00:00, Japan as UTC+09:00, and Sydney as UTC+10:00. But in January, Sydney observes UTC+11:00, and in July, UK observes UTC+01:00, so the differences between all these countries vary during the year. Since lists avoid taking complicated daylight saving time into account, they give wrong information about actual time.
Damage to a German steel facility occurred during a DST transition in 1993, when a computer timing system linked to a radio time synchronization signal allowed molten steel to cool for one hour less than the required duration, resulting in spattering of molten steel when it was poured. [88] Medical devices may generate adverse events that could harm patients, without being obvious to clinicians responsible for care. [89] These problems are compounded when the DST rules themselves change; software developers must test and perhaps modify many programs, and users must install updates and restart applications. Consumers must update devices such as programmable thermostats with the correct DST rules or manually adjust the devices' clocks. [90] A common strategy to resolve these problems in computer systems is to express time using the Coordinated Universal Time with no offset (UTC±00:00; which, depending on time of year, is not always the same as hour as London time) rather than the local time zone. For example, Unix-based computer systems use the UTC-based Unix time internally.
Some clock-shift problems could be avoided by adjusting clocks continuously [91] or at least more gradually [92] —for example, Willett at first suggested weekly 20-minute transitions—but this would add complexity and has never been implemented.
DST inherits and can magnify the disadvantages of standard time. For example, when reading a sundial, one must compensate for it along with time zone and natural discrepancies. [93] Also, sun-exposure guidelines such as avoiding the sun within two hours of noon become less accurate when DST is in effect. [94]
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Daylight saving time (DST), also referred to as daylight savings time, daylight time, or summer time, is the practice of advancing clocks during warmer months so that darkness falls at a later clock time. The typical implementation of DST is to set clocks forward by one hour in either the late winter or spring, and to set clocks back by one hour in the fall or autumn to return to standard time. As a result, there is one 23-hour day in early spring and one 25-hour day in the middle of autumn.
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Shift work is an employment practice designed to keep a service or production line operational at all times. The practice typically sees the day divided into shifts, set periods of time during which different groups of workers perform their duties. The term "shift work" includes both long-term night shifts and work schedules in which employees change or rotate shifts.
Non-24-hour sleep–wake disorder is one of several chronic circadian rhythm sleep disorders (CRSDs). It is defined as a "chronic steady pattern comprising [...] daily delays in sleep onset and wake times in an individual living in a society". Symptoms result when the non-entrained (free-running) endogenous circadian rhythm drifts out of alignment with the light–dark cycle in nature. Although this sleep disorder is more common in blind people, affecting up to 70% of the totally blind, it can also affect sighted people. Non-24 may also be comorbid with bipolar disorder, depression, and traumatic brain injury. The American Academy of Sleep Medicine (AASM) has provided CRSD guidelines since 2007 with the latest update released in 2015.
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Shift work sleep disorder (SWSD) is a circadian rhythm sleep disorder characterized by insomnia, excessive sleepiness, or both affecting people whose work hours overlap with the typical sleep period. Insomnia can be the difficulty to fall asleep or to wake up before the individual has slept enough. About 20% of the working population participates in shift work. SWSD commonly goes undiagnosed, so it's estimated that 10–40% of shift workers have SWSD. The excessive sleepiness appears when the individual has to be productive, awake and alert. Both symptoms are predominant in SWSD. There are numerous shift work schedules, and they may be permanent, intermittent, or rotating; consequently, the manifestations of SWSD are quite variable. Most people with different schedules than the ordinary one might have these symptoms but the difference is that SWSD is continual, long-term, and starts to interfere with the individual's life.
In conservation and energy economics, the rebound effect is the reduction in expected gains from new technologies that increase the efficiency of resource use, because of behavioral or other systemic responses. These responses diminish the beneficial effects of the new technology or other measures taken. A definition of the rebound effect is provided by Thiesen et al. (2008) as, “the rebound effect deals with the fact that improvements in efficiency often lead to cost reductions that provide the possibility to buy more of the improved product or other products or services.” A classic example from this perspective is a driver who substitutes a vehicle with a fuel-efficient version, only to reap the benefits of its lower operating expenses to commute longer and more frequently."
Light effects on circadian rhythm are the effects that light has on circadian rhythm.
Most of the United States observes daylight saving time, the practice of setting the clock forward by one hour when there is longer daylight during the day, so that evenings have more daylight and mornings have less. Exceptions include Arizona, Hawaii, and the overseas territories of American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the United States Virgin Islands. The Uniform Time Act of 1966 established the system of uniform daylight saving time throughout the US.
As of 2022, daylight saving time is used in the following Asian countries:
Till Roenneberg is a professor of chronobiology at the Institute of Medical Psychology at Ludwig-Maximilian University (LMU) in Munich, Germany. Roenneberg, in collaboration with Martha Merrow, explores the impact of light on human circadian rhythms, focusing on aspects such as chronotypes and social jet lag in relation to health benefits.
Sleep deprivation - the condition of not having enough sleep - is a common health issue for students in higher education. This issue has several underlying and negative consequences, but there are a few helpful improvements that students can make to reduce its frequency and severity.
The Sunshine Protection Act is a proposed United States federal law that would make U.S. daylight saving time permanent, meaning the time would no longer change twice per year. The bill has been proposed during several sessions of Congress. In 2022, the Senate passed the bill by unanimous consent, although several senators stated later that they would have objected if they had known that the bill could pass. No iteration of the bill has passed the House.
Establishing either permanent standard or daylight saving time (DST) eliminates the practice of semi-annual clock changes, specifically the advancement of clocks by one hour from standard time to DST on March 8–14 and the retraction of clocks by one hour from DST to standard time on November 1–7.
Johanna H. Meijer is a Dutch scientist who has contributed significantly to the field of chronobiology. Meijer has made notable contributions to the understanding of the neural and molecular mechanisms of circadian pacemakers. She is known for her extensive studies of photic and non-photic effects on the mammalian circadian clocks. Notably, Meijer is the 2016 recipient of the Aschoff and Honma Prize, one of the most prestigious international prizes in the circadian research field. In addition to still unraveling neuronal mechanisms of circadian clocks and their applications to health, Meijer's lab now studies the effects of modern lifestyles on our circadian rhythm and bodily functions.
Dr. Debra J. Skene is a chronobiologist with specific interest in the mammalian circadian rhythm and the consequences of disturbing the circadian system. She is also interested in finding their potential treatments for people who suffer from circadian misalignment. Skene and her team of researchers tackle these questions using animal models, clinical trials, and most recently, liquid chromatography-mass spectrometry. Most notably, Skene is credited for her evidence of a novel photopigment in humans, later discovered to be melanopsin. She was also involved in discovering links between human PER3 genotype and an extremely shifted sleep schedules categorized as extreme diurnal preference. Skene received her Bachelor of Pharmacy, Master of Science, and Ph.D. in South Africa.
Ken-Ichi Honma is a Japanese chronobiologist who researches the biological mechanisms underlying circadian rhythms. After graduating from Hokkaido University School of Medicine, he practiced clinical psychiatry before beginning his research. His recent research efforts are centered around photic and non-photic entrainment, the structure of circadian clocks, and the ontogeny of circadian clocks. He often collaborates with his wife, Sato Honma, in work involving the mammalian suprachiasmatic nucleus (SCN), its components, and associated topics.
Chronodisruption is a concept in the field of circadian biology that refers to the disturbance or alteration of the body's natural biological rhythms, particularly the sleep-wake cycle, due to various environmental factors. The human body is synchronized to a 24-hour light-dark cycle, which is essential for maintaining optimal health and well-being. However, modern lifestyles, which involve exposure to artificial light, irregular sleep schedules, and shift work, can disrupt this natural rhythm, leading to a range of adverse physiological outcomes. Chronodisruption has been linked to a variety of health issues, including neurodegenerative diseases, diabetes, mood disorders, and cancer. Such disruptors can lead to dysregulation of hormones and neurotransmitters, though research continues to fully understand the physiological implications of chronodisruption. Indeed, research in chronobiology is rapidly advancing, with an increasing focus on understanding the underlying mechanisms of chronodisruption and developing strategies to prevent or mitigate its adverse effects. This includes the development of pharmacological interventions, as well as lifestyle modifications such as optimizing one’s sleeping environment and timing of meals and physical activity.
... the Minneapolis Star, Jan. 28, 1959 ... [stated] 'Farmers complained that they cannot get into the fields any earlier than under standard time ... because the morning sun does not dry the dew "on daylight savings time." '
In fact, the best studies we have prove that Americans use more domestic electricity when they practice daylight saving. Moreover, when we turn off the TV and go to the park or the mall in the evening sunlight, Americans don't walk. We get in our cars and drive. Daylight saving actually increases gasoline consumption, and it's a cynical substitute for genuine energy conservation policy.
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