Additional Math Pages & Resources

Wednesday, September 23, 2009

Daylight "saving" time?

Most of the US observes Daylight Saving Time (DST). Unless you live in part of Arizona, or all of Hawaii, American Samoa, Guam, Puerto Rico, the Virgin Islands, etc. you know the twice-a-year hassle of resetting all your clocks.

We are not alone in using DST. Other countries have similar systems, often called Summer Time.

Does this practice save Daylight? No.
Does it save Time? No.
Energy? Perhaps. Studies disagree.

Does it save ink or words or Angst? No, obviously not.

At this point I offer you 3 choices:
  1. Stop reading. You know DST doesn't end for a month. Why worry about it now...
  2. Check out my summary below on daylight saving time.
  3. Read the actual law for yourself.  A small sample might deter you from this path:  
During the period commencing at 2 o’clock antemeridian on the second Sunday of March of each year and ending at 2 o’clock antemeridian on the first Sunday of November of each year, the standard time of each zone established by sections 261 to 264 of this title, as modified by section 265 of this title, shall be advanced one hour and such time as so advanced shall for the purposes of such sections 261 to 264, as so modified, be the standard time of such zone during such period; however, (1) any State that lies entirely within one time zone may by law exempt itself from the provisions of this subsection ...

Let's look at how it came about.


Standard time zones were introduced in the US and Canada by the railroads in 1883. Prior to this development, time in each local area was determined by the sun overhead at high noon method.

The 1918 Standard Time Act made time zones official. Details of making it work were left to the Interstate Commerce Commission, which controlled train schedules. The bill also established DST.

Due to constant bickering and complaining, DST was repealed in 1919. It was re-established nationally during World War II, ending in September 1945. After the war, observance varied depending on where you lived.

The 1966 Uniform Time Act formalized a national DST beginning 2am on the last Sunday in April and ending on the last Sunday in October. Responsibility was shifted to the Department of Transportation (trains, planes and buses).

During the "energy crisis of 1974", Congress temporarily set the starting days as Jan 6, 1974 and Feb 23, 1975, then DST reverted back to the last Sunday in April.

The 1986 Public Law 99-359 shifted the starting date to the first Sunday in April, 1987. The ending date remained the last Sunday in October.

The 2005 Energy Policy Act changed the starting date to the second Sunday in March and the ending date to the first Sunday in November.


In California we are interested in conservation, so I thought I'd look at our state's energy saving analysis. The most recent report's statisticians say we might save a little electricity, or consume a little more. Apparently they're not sure:

... the absence of statistical confidence does not mean there is no effect. It is entirely possible that early DST saved electricity as people used less light and heat in the evenings. It also could have increased electricity use, with morning increases outweighing evening savings.    DST ... had no statistically significant effect on total daily electricity use in the month of March 2007 in 80% of California [primarily using electricity for energy]. The regressions did not and cannot rule out small savings, nor  can they rule out an electricity use increase.   

If you would like to audit their statistical regressions, here you go. It's over my head.


A recent study in Indiana indicated that the state uses MORE energy due to Daylight Saving time.


None of these bills addressed the difficulty of or energy consumed by adjusting and resetting clocks and watches. Over 1.1 billion wrist watches are sold new each year; most must be adjusted for DST. The millions of clocks now found in microwaves, thermostats, cameras, digital video recorders, etc. also require resetting twice a year. The hardest job seems to be the clocks in our cars!

If you have an Infinity (nice symbolism, eh?), here's how you do it:

  1. Make sure car is not moving and is in Park or Neutral (if moving or in Drive you cannot set the time).
  2. Open your GPS display.
  3. Click the "OK" button at the initial language choice screen.
  4. When the map appears on the screen, click the "Settings" button.
  5. From the settings tab, highlight and click the "Clock" option with the joystick at the right of the console.
  6. The time display should be at the top of the screen. Move the joystick to the left and right to adjust the time.

Subjectively, I'd say the energy expended on DST exceeds the energy saved. But nobody seems to care about energy used by people, just energy consumed by machines ...

No comments:

Post a Comment

Type your comment here