44

Since the US recently went on to DST, I thought it'd be appropriate to ask this:

I've heard many claims made about DST, ranging from "It saves electricity" to "It balances out daylight hours" to "It gives people more sunlit free time in the evenings." Which of these claims are true, and what evidence supports those claims?

Edit: I should probably consider both positive and negative effects, and not just benefits. Question title edited to reflect that.

  • 2
    Scientifically established? None. The Wikipedia article on the topic is very good. – Lennart Regebro Mar 14 '11 at 3:47
  • Well to be honest, "more free time in daylight in the evenings" is not something you really need to check scientifically. Other things being equal, if you start work earlier you finish earlier. Nevertheless very good question, looking forward to answers. – user288 Mar 14 '11 at 23:25
  • 2
    There's a TRC episode that discusses this. From what I recall, the conclusion was that the energy effect was negligible, but there was a significant decrease in car accidents. I might remember that incorrectly, especially the "significant" part. You'd have to listen in for yourself (hence the comment, and not an answer). The SciAm article was probably a great deal of the source material, anyway :) – David Hedlund Mar 15 '11 at 21:50
  • I am disappointed that the answers and comments are not more focussed on latitude, which has a big effect on how popular daylight savings is. – Oddthinking Aug 4 '14 at 6:02
  • 1
    @Oddthinking, tell us more (about latitude). – ctrl-alt-delor Dec 24 '16 at 9:40
21

I read a Scientific American article on this a while back. It had this to say about Daylight Savings in the USA:

People may think that with the time shift, they are conserving electricity otherwise spent on lighting. But recent studies have cast doubt on the energy argument—some research has even found that it ultimately leads to greater power use.

The observed drop in energy use of 0.2 percent fell within the statistical margin of error of 1.5 percent.

The article also addresses concerns about an increase in heart attacks, but also lowered traffic accidents. In today's society, I think that the idea persists mostly out of momentum more than sound science.

  • 6
    Can you find any more information or studies? The SciAm article is a start, but doesn't cite a lot of hard data. – Larian LeQuella Mar 15 '11 at 2:36
  • I think this is quote from that article worth including: "Examining electricity usage and billing since the statewide change, Kotchen and his colleague Laura Grant unexpectedly found that daylight time led to a 1 percent overall rise in residential electricity use, costing the state an extra $9 million. " – vartec Oct 25 '13 at 15:40
18

In 2008 there was a study published that showed DST wastes energy in Indiana. The authors took advantage of the fact that Indiana legislated state-wide DST in 2006, whereas prior to that they had per-county DST or non-DST. They used the individual home meter readings from the utility company to conclude that DST wasted energy overall.

Focusing on residential electricity demand, we conduct the first-ever study that uses micro-data on households to estimate an overall DST effect. The dataset consists of more than 7 million observations on monthly billing data for the vast majority of households in southern Indiana for three years. Our main finding is that—contrary to the policy's intent—DST increases residential electricity demand. Estimates of the overall increase are approximately 1 percent, but we find that the effect is not constant throughout the DST period. DST causes the greatest increase in electricity consumption in the fall, when estimates range between 2 and 4 percent.

  • 1
    I imagine that this would vary greatly with latitude and longitude of the study area within a time-zone. – Richard A Sep 2 '11 at 3:13
  • 1
    This is about domestic power usage. But what about business power usage? supermarkets, cinemas, industries... – Envite Aug 4 '14 at 11:59
11

Since this question was posted, there have been many more studies in the literature about the effects of DST. Here I just summarize the first 13 papers (some are gated) that show up on Google Scholar ("Daylight Saving Time", with filter 'since 2010')

My tl;dr conclusion: Most but not all say DST is bad.

Energy-related

(1) uses a natural experiment in Indiana:

DST saves on electricity used for illumination but increases electricity used for heating and cooling. ... the latter effect is larger ... DST costs Indiana households an average of $3.29 per year in increased electricity bills, which aggregates to approximately $9 million for the entire state. Finally, the social costs in terms of increased pollution emissions range between $1.7 and $5.5 million per year.

(11) finds that in India (which does not currently have DST) will benefit more by advancing the current Indian Standard Time by half an hour, than by adopting DST.

(12) finds that DST reduces electricity consumption by at least 1.0% in both Norway and Sweden.

Sleep/Health/Accidents/Productivity-related

(2) looks at data from Swedish Heart Intensive Care Admission and finds

an elevated incidence ratio of 1.039 [for Acute Myocardial Infarction] for the first week after the spring clock shift forward.

(3) finds "a dramatic increase in cyberloafing behavior".

(4)'s abstract states very tentatively that

Indirect evidence of an increase in traffic accident rates, and change in health and regulatory behaviours which may be related to sleep disruption suggest that adjustment to daylight saving time is neither immediate nor without consequence.

(5)'s abstract suggests that sleep-adjustment difficulties is severest for those who habitually sleep less than 7.5 hours.

(6) looks at Finnish data and concludes: "It seems that sleep deprivation after DST transition is not harmful enough to impact on occupational accident rates." (10) is by some of the same authors and has a similar conclusion.

(8) finds a "rise in Road Traffic Collision related injury figures up to two weeks following the spring time transition." (9) seems to be just an updated version of (8) with the same conclusion.

(13) finds that DST lowers SAT scores.

Other

(7) states there is an "economically large negative daylight-saving effect in U.S. stock returns".

Sources (Journal publication date in parentheses)

(1) Does Daylight Saving Time Save Energy? Evidence from a Natural Experiment in Indiana (Nov 2011)

(2) Daylight saving time shifts and incidence of acute myocardial infarction – Swedish Register of Information and Knowledge About Swedish Heart Intensive Care Admissions (RIKS-HIA) (Mar 2012)

(3) Lost sleep and cyberloafing: Evidence from the laboratory and a daylight saving time quasi-experiment. (Sep 2012)

(4) The impact of daylight saving time on sleep and related behaviours (Aug 2013)

(5) Individual response to the end of Daylight Saving Time is largely dependent on habitual sleep duration (2013)

(6) Work-related accidents and daylight saving time in Finland (Nov 2010)

(7) EFFECTS OF DAYLIGHT-SAVING TIME CHANGES ON STOCK MARKET RETURNS AND STOCK MARKET VOLATILITY (Feb 2013)

(8) DAYLIGHT SAVINGS TIME (DST) TRANSITION: THE EFFECT ON SERIOUS OR FATAL ROAD TRAFFIC COLLISION RELATED INJURIES (2011)

(9) THE EFFECTS OF DAYLIGHT SAVING TIME (DST) TRANSITION ON SERIOUS OR FATAL ROAD TRAFFIC INJURIES IN GREAT BRITAIN: AN ANALYSIS OF TWO INDEPENDENT NATIONAL DATASETS

(10) Daylight Saving Time Transitions and Road Traffic Accidents (2010)

(11) Year-round daylight saving time will save more energy in India than corresponding DST or time zones (March 2012)

(12) The impact of daylight saving time on electricity consumption: Evidence from southern Norway and Sweden (June 2011)

(13) Detrimental effects of daylight-saving time on SAT scores (Feb 2011)

  • 3
    I see an unsurprisingly direct correlation between the latitudes of the countries you mention, and the positive attitude to Daylight Savings. India and Indiana are much closer to the equator than Sweden or Finland. – Oddthinking Aug 4 '14 at 5:58
  • (12), is interesting, it seems to be the only one with something positive to say (the others are ether negative or no negative affects found). I would like to see this repeated with the daylight-saving time-zone, used all year. I hypothesise that this would save even more energy (I.e it is not the twice yearly shift that causes the saving, but the choice of time-zone). – ctrl-alt-delor Dec 24 '16 at 10:06

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