As a foreigner, United States has a very complex time system for me. Central Time Zone, North American Eastern Time Zone, Mountain Time Zone, Alaska Time Zone, Pacific Time Zone, Samoa Time Zone, Atlantic Time Zone, Hawaii–Aleutian Time Zone. And also plus DST (Daylight saving time).

I heard people saying this can save a lot of energy. I want to know if there is any scientific report to support this. Or it's just people they like this system. Thanks


closed as off topic by David Z Mar 27 '13 at 23:06

Questions on Physics Stack Exchange are expected to relate to physics within the scope defined by the community. Consider editing the question or leaving comments for improvement if you believe the question can be reworded to fit within the scope. Read more about reopening questions here. If this question can be reworded to fit the rules in the help center, please edit the question.

  • 1
    $\begingroup$ You do realize time zones are used everywhere in the world (except China) in exactly the same way? It's just most countries are not large enough to span multiple ones. Daylight savings time is a different story, and probably has more to do with politics than energy, but I'll let someone else chime in. $\endgroup$ – user10851 Mar 27 '13 at 17:19
  • $\begingroup$ LOL, I know, I know (I'm a Chinese), so you think without using time zones, it will waste a lot of energy? We once tried for a year when I was young, but later we gave up. The reason I am asking here is I am more concerned about scientific proof, I want to see the report. $\endgroup$ – Daniel Mar 27 '13 at 17:26
  • 1
    $\begingroup$ I don't think time zones have much to do with energy. Everyone just wants sunrise, noon, sunset, etc. to be at about the same time. Before timezones, every town would have its own local noon, off by a bit from the next town. In the US, it was the railroads invented timezones so that train schedules would make more sense - instead of thousands of different times, there were only 4. China just went the extra step and made a single time zone - unity at the expense of "normal" sunrise/set times in the western part of the country. $\endgroup$ – user10851 Mar 27 '13 at 17:32
  • 1
    $\begingroup$ My hunch is DST could help various business interests who would benefit from more daylight hours after working hours during the summer, but I don't know the full history. $\endgroup$ – user10851 Mar 27 '13 at 17:33
  • 3
    $\begingroup$ I'm not really sure if this is on topic for this site. Whatever scientific evidence there may be on the topic of whether daylight savings time reduces energy usage, it seems unlikely to be part of physics. But perhaps the question could be migrated to Skeptics with a little fixing up. $\endgroup$ – David Z Mar 27 '13 at 17:54

Time zones

enter image description here

Moving on from the calendar to time, we recommend the abolition of all time zones, as well as of daylight savings time, and the adoption of atomic time—in particular, Greenwich Mean Time, or Universal Time, as it is called today. Like the adoption of a modern calendar, the embrace of Universal Time would be beneficial.

For example, the adoption of Universal Time would give new flexibility to economic management in the vast East-West expanse of Russia: everyone would know exactly what time it is everywhere, at every moment. Opening and closing times of businesses could be specified for every class of business and activity. If thought desirable, banks and financial institutions throughout the country could be required to open and to close each day at the same hour by the world time. This would mean that bank employees in the far East of Russia would start work with the sun well up in the sky, while bank employees in the far west of Russia would be at their desks before the sun has risen. But, across the country, they could conduct business with one another, all the working day. (This would have a second benefit: at least in the far east and far west, the banks would be open either early, or late, convenient for those who are working “sunlight hours,” such as farmers.)

With Universal Time, agricultural workers, critically dependent on the position of the sun, could rise with the sun, without producing any impact on other aspects of cultural and economic life. The readings on the clocks, and the date on the calendar, would be the same for all. But, times of work would be attuned with precision to Russia’s local and national needs. China already has adopted a single time zone for the same purposes. And all aircraft pilots, worldwide, use Universal Time exclusively, for exactly the same reason that we are advocating its broad adoption—plus avoiding collisions.

Moscow could introduce both a simplified calendar, identical each year (harmonized with the seasons by rare full-week adjustments at year’s end), and Universal Time, which would abolish the International Date Line, making the date and the time identical everywhere, including Alaska and the farthest eastern regions of Russia. There, and also in the center of the Pacific Ocean, the date would change at 00:00:00, just as the sun passed overhead.

Source and context. Also see this and this for discussion.


One of the biggest reasons we change our clocks to Daylight Saving Time (DST) is that it reportedly saves electricity. Newer studies, however, are challenging long-held reason. A report was released in May 2001 by the California Energy Commission to see if creating an early DST or going to a year-round DST will help with the electricity problems the state faced in 2000-2002.

You can download an Acrobat PDF copy of the staff report, Effects of Daylight Saving Time on California Electricity Use, Publication # 400-01-13, (PDF file, pages, 5.2 megabytes).

The study concluded that both Winter Daylight Saving Time and Summer-season Double Daylight Saving Time (DDST) would probably save marginal amounts of electricity - around 3,400 megawatt-hours (MWh) a day in winter (one-half of one percent of winter electricity use - 0.5%) and around 1,500 MWh a day during the summer season (one-fifth of one percent of summer-season use - 0.20%). Winter DST would cut winter peak electricity use by around 1,100 megawatts on average, or 3.4 percent. Summer Double DST would cause a smaller (220 MW) and more uncertain drop in the peak, but it could still save hundreds of millions of dollars because it would shift electricity use to low demand (cheaper) morning hours and decrease electricity use during higher demand hours.

The Energy Commission has also published a new report titled The Effect of Early Daylight Saving Time on California Electricity Consumption: A Statistical Analysis. Publication # CEC-200-2007-004, May 27, 2007. (PDF file, 592 kilobytes)

A more recent study concludes that Daylight Saving Time in Indiana actually increases residential electricity demand. That study titled "Does Daylight Saving Time Save Energy? Evidence From a Natural Experiment in Indiana". (PDF file) looked at the electricity use when portions of the state finally started to observe DST. Before the new extended DST, portions of Indiana did not observe DST.

Some have wondered whether this study would be true for the entire United States. Initial analysis by staff of the California Energy Commission says a similar study may not yield the same results for California because:

The use of residential air conditioning is relatively low in Indiana, and the saturations are low. Where as California has high usage of air conditioning in the summer.

Heating use is relatively high in Indiana, while it is relatively low in California.

The diurnal variation in temperature is low while California is very high.

Indiana is located in western edge of the same time zone as Maine and Florida, but the sun actually comes up at an earlier time than those other two states.

Indiana's north-south location will affect how long the days are in the summer and might very well lead to different results in different areas.

So, while the analysis is of interest to Indiana, it's conclusions may not be totally correct for California or the rest of the country. The first national study since the 1970s, was mandated by Congress and was done by the U.S. Department of Energy.

The DOE study can be downloaded at: http://www1.eere.energy.gov/ba/pba/pdfs/epact_sec_110_edst_report_to_congress_2008.pdf (PDF file, 285 kb) [Actually: here]

The key findings in the report to Congress are:

The total electricity savings of Extended Daylight Saving Time were about 1.3 Tera Watt-hour (TWh). This corresponds to 0.5 percent per each day of Extended Daylight Saving Time, or 0.03 percent of electricity consumption over the year. In reference, the total 2007 electricity consumption in the United States was 3,900 TWh.

In terms of national primary energy consumption, the electricity savings translate to a reduction of 17 Trillion Btu (TBtu) over the spring and fall Extended Daylight Saving Time periods, or roughly 0.02 percent of total U.S. energy consumption during 2007 of 101,000 TBtu.

During Extended Daylight Saving Time, electricity savings generally occurred over a three- to five-hour period in the evening with small increases in usage during the early- morning hours. On a daily percentage basis, electricity savings were slightly greater during the March (spring) extension of Extended Daylight Saving Time than the November (fall) extension. On a regional basis, some southern portions of the United States exhibited slightly smaller impacts of Extended Daylight Saving Time on energy savings compared to the northern regions, a result possibly due to a small, offsetting increase in household air conditioning usage.

Changes in national traffic volume and motor gasoline consumption for passenger vehicles in 2007 were determined to be statistically insignificant and therefore, could not be attributed to Extended Daylight Saving Time.

Source and further references and context

  • $\begingroup$ Excellent! These kind of information is exactly what I need. I hope there is some research on time zone issues too! $\endgroup$ – Daniel Mar 27 '13 at 18:07
  • $\begingroup$ @Daniel Added stuff on time zones. $\endgroup$ – Keep these mind Mar 27 '13 at 18:51
  • $\begingroup$ 0.02% of total U.S. energy consumption? Seems like more of a hassle than it is worth... $\endgroup$ – OSE Mar 27 '13 at 20:04
  • $\begingroup$ @user2018790 Mind you, this is the difference between DST and EDST, not the difference between DST and no-DST. Also, "[p]otential non-energy impacts include children traveling to school during darkness, traffic accident rates, crime rates, [electronics changeover to new EDST dates, airline schedule changes,] and agricultural work scheduling." $\endgroup$ – Keep these mind Mar 27 '13 at 20:13

Not the answer you're looking for? Browse other questions tagged or ask your own question.