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What are the scientifically established effects of Daylight Saving Time?

If we did not have daylight-saving, then would the days still be longer in the summer?

  • If not, then what is it for?
  • Does it have any advantages? For Who?
  • Can anyone cite any research, that shows its effects?

I can see disadvantages to changing the clocks. But I see no advantages, not even small advantages that are outweighed by the disadvantages. Unless you include job creation and distraction from real issues as advantages.

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ctrl-alt-delor
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    You are misunderstanding daylight saving time. It doesn’t make days *longer* (how would that work?), it just *shifts* the time frame. Because of that, the question obviously makes no sense. – Konrad Rudolph Mar 29 '11 at 13:14
  • @KonradRudolph the question makes perfect sense: I was just not being very sceptical, and assuming that there is a reason for wasting time changing the clocks twice a year, and that maybe the name tells us something. As opposed to the more obvious conclusion that it is just a scam, the the name is marketing-words. However I still wish to know who is benefiting from this scam, and in what way. Or was it just a big mistake. – ctrl-alt-delor Mar 18 '15 at 18:49

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The length of a day, or to be more precise the number of hours in a 24-hour period in which there is sun-light is a result of a relation between the earth and the sun. Daylight saving time, which is changing the official hour of the day, doesn't change the positions of the earth and the sun and therefore does not effect number of hours in which there is sun-light and doesn't, in fact, "saves" any day-light.

That, however, is not the whole story. Usually, we define the "day" as the time period in which we are awake and night as the period in which we are asleep. Note that these definitions differ from the previous ones since we (in our modern life) don't usually get up with the crack of dawn and go to sleep when the sun sets. Now, if we were to most of our activities during day-light - than we could save quite a lot of money on, for example, lighting the room.

And that is what people mean when they talk about saving day-light. There is exactly the same amount of day-light hours, but we are awake during more of them and thus saving money. Now we could do that simply by deciding to get up earlier and do all of our activities earlier. However, since that seems to confuse people (for example, we are used to have our TV programs, bank opening time and so on at a given hour), we simply move the watch instead and get the exact same effect.

As to how many day-light hour are actually "saved" (are actually been put into use by us), that depends on by how much we have moved the watch - typically, an hour.

Noam Weiss
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  • But in the winter it is dark when I awake and go to sleep, and in the summer it is light when I awake and go to sleep. Would it also work, just as well if we kept saving-time on all year? – ctrl-alt-delor Mar 29 '11 at 14:02
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    @richard: In spring (or other times), do you sometimes rise after sunrise and go to sleep after sunset? If so, it has an effect on those days. – Henry Mar 29 '11 at 14:22
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    @richard: the idea is to use as much day-light as possible. In some cases, it's irrelevant (either there is not enough day-light anyway, or there is more than we need) - in many cases (Henry's example of spring is a good one), it is relevant. When the days start to get longer and the sun rises before we get up, than it is a good idea to start getting-up earlier, that is moving to day-light saving time. When the days get shorter and the sun rises later it is time to stop day-light saving time (because it's better to get-up when there is already light). – Noam Weiss Mar 29 '11 at 15:44
  • @Henry and Noam, So you have explained perfectly the propaganda, but does it work. Does it save money, energy, lives, anything. The only research I could find on the subject, shows that it costs lives, and wastes time (both in the transition). – ctrl-alt-delor Jul 04 '14 at 09:35
  • What we need to do is shift the summer daylight hours to winter, by changing the *speed* of the clock during daytime. I think that is really what we should do. It would be nice to make working hours "longer" and vacation hours "shorter" also, as good citizens. –  Jan 20 '16 at 01:36