Of That

Brandt Redd on Education, Technology, Energy, and Trust

06 November 2010

How Much Daylight Do You Save?

Shortcut: Click Here for the Daylight Saving Calculator

Tonight most of us in North America get to sleep an extra hour as we go off of Daylight Saving Time. Before 2007 the shift would already happened. The US Energy Policy Act of 2005 added four weeks to Daylight Saving time. The end of daylight savings was delayed by one week in the fall (possibly to keep it lighter for trick or treaters) and it now starts three weeks earlier in the spring. These changes took effect in 2007.

I've always been skeptical of the value of Daylight Saving Time. Though I'm not great at it, I still subscribe to Benjamin Franklin's admonishment, "Early to bed and early to rise makes a man healthy, wealthy and wise. Having the sun rise and set later reduces the incentive to rise and retire early. Ironically, Franklin is widely credited with inventing daylight savings time. In fact, his writings on the subject were satirical.

Three years ago, when the new daylight rules took effect, I decided to find out how much daylight is really saved. The theory of Daylight Saving is that any daylight before you rise from bed is daylight "lost." Therefore, the amount of daylight you "save" will depend on three things: your latitude, your longitude and the time you wake up in the morning. Here's why:
  • Latitude: The higher your latitude -- the further you are from the equator -- the more dramatically the length of the day changes between winter and summer. Above the arctic circle, the sun says up for days or weeks in the summer and sets for the same amount if time in midwinter.
  • Longitude: If you are at the Eastern edge of your timezone the sun will rise approximately an hour earlier than on the Western edge.
  • Rise Time: If you rise before the sun and retire after it sets then there is no daylight to be saved. Any daylight to be saved is between sunrise and "you rise."
With that in mind, I put on my programmer hat and wrote my Daylight Savings Calculator. This calculator takes the city you live in and your rise time and calculates how much daylight is saved under the old and new US rules. If your city isn't listed, you can choose one nearby or enter your latitude, longitude and timezone. It has a few limitations: If you enter a latitude above the Arctic Circle it does strange things. Also, it follows US rules for daylight saving regardless of your location. So, if you enter a latitude in the Southern hemisphere it will accurately plot the length of the days but the calculations of daylight to be saved will be really wrong.

Click here to try it out!

With my recent move to Seattle it's interesting to see how much more dramatic the lay-length shifts are. Using a rise time of 6:30am, I saved 149 hours of daylight in Provo and save 181 hours of daylight in Seattle.

Despite these savings of daylight, I'm still skeptical about whether the savings result in a net benefit or liability. The Wikipedia article on the subject discusses energy use, economic effects, public safety and health. Overall, there's more controversy than conclusion. 


  1. I save only one hour according to your formula. Big whoop, I want to say.

  2. Finally! Scientific confirmation that the whole business is worthless. My 5 am rise in Salt Lake shows I save 1 hour of daylight -- which I use changing the clocks!

    It's amazing that we institutionalize this insanity. I recognize that it does add to the profit margins of the golf courses. For that we can be grateful ;-}