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DST was observed in many countries last week-end (28-29.10.2017). This article tells us about the origin of DST:

Agrarian cultures built their societies around sunlight, waking up with the sun to toil in the field and heading home as the sun lowered beneath the horizon. But the industrial revolution brought with it the freedom to unshackle us from nature's clock.

As long ago as 1897, countries around the world began instituting daylight saving time, adding an hour of sunlight to the afternoon. This meant communities could be more productive — people could work longer, and when work was done it was still bright enough to run errands and stimulate the economy. The added daylight also meant more exposure to vitamin D and the added time for people to exercise outdoors.

However, this has changed a lot since then, as most Western countries has a small agricultural sector (less than 5%). Lighting can be obtained much more efficiently than in the past (e.g. LED bulbs).

There are several pros and cons related to DST covering energy usage, economic effects, public safety and health. However, it is clear that it affects the the Circadian Rhythm and adds some complexity for time computations, as DST is not uniformly applied.

Question: Why is Daylight saving time (DST) still used in so many Western countries?

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    Never understimate the power of inertia. Also, as programmer, the issues with computations are largelly solved by now; introducing changes would cause new issues in programs that work perfectly now. For example, there were issues because in 2007 the Australian government introduced (or removed?) DST and MS refused to issue patches for out-of-support products (intelliadmin.com/index.php/2007/01/…) – SJuan76 Oct 31 '17 at 9:37
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    Most of the modern advantages of daylight saving aren't to the agrarian community (livestock are still driven by the sun), but to schoolchildren and workers with a fixed daily finish time. – origimbo Oct 31 '17 at 11:45
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    In the late 1960s Britain experimented with keeping Summer Time (BST) all through the winter. (We revert to GMT between end Oct and end March, which is one hour behind BST). During the experimental period it was discovered that road accidents involving schoolchildren (especially in Scotland and northern England) increased. The difficulty is, during short winter days to get kids to and from school in daylight. During WW2 retain had "double Summer Time" - 2 hours ahead of GMT. But that was largely for agricultural reasons. – WS2 Oct 31 '17 at 14:22
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    There may be less people doing the farming, but it's not like we need less food. That just means fewer entities doing it on larger scales, individually. The agricultural need has not diminished. – PoloHoleSet Oct 31 '17 at 15:37
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    @jamesqf If you change school hours it doesn't just affect children. The parents who take and collect them would also have their day changed, which might not fit in with their employment. The people who bring deliveries to the school would have to adjust to different times. The same sorts of problems apply to agriculture. We live in integrated societies and if one segment changes its hours it has implications elsewhere. Far simpler just to change the clocks. Besides, I enjoy the extra hour in bed in October, in return for losing one in March. I'm used to it and it has become part of life. – WS2 Nov 1 '17 at 16:59
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Daylight Saving Time is used because the governments (who get to decide these matters) believe it to be beneficial.

You have already noted the arguments for Summer Time: The later sunset is said to save energy for lighting, and reduce traffic accidents. However in winter it is said to be beneficial to be closer to solar time, as it avoids dark mornings and allows for children to get to school and more workers to work in the light.

You are also aware of the claimed disadvantages: Disruption when the clocks change, difficulties of time calculations, more heart attacks in the spring when clocks go forward.

It is a matter of judgement for the government whether these apparent benefits outweigh the disadvantages. At the moment many governments believe they do.

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    The later sunset is said to save energy for lighting, and reduce traffic accidents what about the morning, then ?? – Bregalad Nov 1 '17 at 21:02
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    I'm not making a case for or against DST, I'm just repeating the arguments, for clarity. – James K Nov 1 '17 at 21:27
  • How many lives are saved by driving at virtual 6PM vs actual 6PM compared with the actual measured increase in the road toll for a couple of days when the clocks move? – mcottle Nov 2 '17 at 2:10
  • In Britain it was only the arrival of the railways in the 1840s that caused the time throughout the whole country to be standardised. Some people talk as if the adjusting of the clocks is some sort of socialist plot to make everyone uniform. Perhaps they think that every family should set its own time! That really would be fun! – WS2 Nov 2 '17 at 10:04
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    Are you sure the governments consider having it is beneficial? Most of the talk on the topic I've heard is people realizing it has net negative benefits, but not being willing to carry the cost of getting rid of it. – Erik Nov 2 '17 at 19:25

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