How-To Geek

Daylight Saving Time Visualized

When you map out the Daylight Saving Time adjusted sunrise and sunset times over the course of the year, an interesting pattern emerges.

Chart designer Germanium writes:

I tried to come up with the reason for the daylight saving time change by just looking at the data for sunset and sunrise times. The figure represents sunset and sunrise times thought the year. It shows that the daylight saving time change marked by the lines (DLS) is keeping the sunrise time pretty much constant throughout the whole year, while making the sunset time change a lot. The spread of sunrise times as measured by the standard deviation is 42 minutes, which means that the sunrise time changes within that range the whole year, while the standard deviation for the sunset times is 1:30 hours. Whatever the argument for doing this is, it’s pretty clear that reason is to keep the sunrise time constant.

You can read more about the controversial history of Daylight Saving Time here.

Daylight Saving Time Explained [via Cool Infographics]

Jason Fitzpatrick is a warranty-voiding DIYer who spends his days cracking opening cases and wrestling with code so you don't have to. If it can be modded, optimized, repurposed, or torn apart for fun he's interested (and probably already at the workbench taking it apart). You can follow him on if you'd like.

  • Published 11/6/12

Comments (15)

  1. Lawrence Garvin

    This is a great example of confusing correlation with causation, and to be frank, some simple research will readily identify exactly why Daylight Savings Time was created — and it had absolutely nothing at all to do with managing sunrise times, but everything to do with extending sunset times.

    The primary benefit, as originally implemented, was to reduce electrical consumption in the evening hours by extending the amount of daylight available to the population. Generally this has not had the intended results — the reasons why are an entirely different discussion.

    The fact that the std dev of sunrise times is significantly smaller is purely a coincidence.
    The fact that the std dev of sunset times is significantly larger is exactly the intended result.

  2. Rob

    So, next time it comes around, lets all change 1/2 hour and LEAVE IT THERE FOREVER!

  3. Murphy

    This year I decided not to change to the winter time. I can start a job in a flexible hours (between 7 and 9:30). Before I started a work at 8:30 and now at 7:30, which for my biological clock is the same time. In spring I will be back with new summer time and no side effects from the change. :)

  4. Ronny

    @Lawrence Garvin,
    Daylight Saving (not Savings) Time.

  5. Polbeer91


    I think you’re right as to why DST was created, but it is, in my opinon the same as what the maker of the graph states.
    The way we can extend the amount of light in the evening hours is by making sure none of it is wasted in the morning hours (while we are still asleep), thus making the sunrise times constant.

  6. Nic In UK

    British Summer Time as we call it over here was implemented in WWII to enable farmers to work longer in the evening to aid productivity, whilst maintaining a reasonably constant time for milking as most farms then were mixed [Dairy & Arable]. With the large deviation of day length at our latitude, it as possible to harvest in the fields until 10 or even 11 pm without powerful lights and still milk the cows morning and evening. We’d like to ditch it now because it doesn’t, as many people believe give you anymore daylight, just moves the daylight hours a little to fit the work pattern, but we’ll have to wait until Scotland becomes independent because they are always complaining that “the wee kids have to go to school in the dark”. Wait till they go to work!

  7. Full Noodle Frontity

    I have to wonder what the point is in saving all that daylight if we can’t make a withdrawal when it’s dark.

  8. ProstheticHead

    @Nic in UK

    +1, although if it were up to me I’d but the clocks back about four hours so I can have some sunlight for leisure activities when I get home in the evening. It’s kind of difficult to motivate oneself to do things when you go to work in the dark, then it’s pretty much dark again by the time you get home.

  9. James

    It is still stupid whatever the reason.

  10. CF

    The reason daylight saving time was instituted was, as Nic(in the UK) stated – to provide extra productivity-time for the farmers and extra daylight productivity and/or leisure-time for the factory workers(of those days). That reason no longer exists given such concepts as flex-time and modern technology.

    The concept of daylight saving time no longer is valid and, as so well stated in earlier posts, ought to be eliminated. Lets have the politicos do away with the process, pick a constant time system and then stay with it throughout the year. Quit screwing around with what nature has established and, I might add,seemed to function quit well without the help of we humans( in our arrogance) prior to WWII.

  11. DaveS

    DST is still quite valid for those of us who live between 35 and 50 latitudes.

    Where I live ~40N in summer sunset is 7:30PM if we don’t adjust the clocks, and sunrise around 4:15AM
    That means about 2 hours of ‘wasted’ daylight in the morning for your average person.

    I much prefer the 8:30PM sunsets we have while DST is in effect. Gives more time for outdoor leisure activities after work.

    Those of you above 50N especially won’t see all that much sense in DST it because your day length is long enough that even w/o the DST adjustment, summer sunset is still past 9PM and 10PM. Ample time already to enjoy summer weather (whatever that might actually mean so far north)

  12. Nick

    DST was implemented for the reasons Nic mentions, but it was during WW1 not 2. Germany and her allies were first, the intention being to conserve coal. Everybody else soon followed with the US finally in 1918.

  13. Joe

    Did any of you guys try living in Norway? Especially in the very north… DST only come into effect in the mid spring and the mid fall. ;-D

  14. Gordon Robbins

    No, here’s the REAL reason why Daylight Savings time change was created. It was a JOKE. But as it was a joke told by Ben Franklin everyone thought it was brilliant, and we’ll never get rid of it!
    Thanks a heck of a lot, Ben! X-/

  15. Wayne Riker

    I hear scuttlebut about dumping local time all together and using UT (Universal Time). All computers use UT and convert to local time just for the user. I.e.: all file creation dates and modifications are recorded on the diskdrive as UT time. some groups are saying this will work universally. So, everyone gets up in the morning at different times from zone to zone (comparitively – as the zones would not exist after a switch to UT).

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