Understanding Daylight Saving[s] Time

[Note: Some have noted that it should be DaylightSaving Time, without the pluralization of Saving. I, likemany, use it more as a general-use title rather than a literalstatement – given that it isn’t actually saving daylight – and Igenerally hear it referred to as Daylight Savings Time. Justthought I should mention that.

If one wants to be a pedant, I believe it should actually beDaylight-Saving Time]

The Ontario government caved today, rashly deciding to follow the lead of a ludicrous U.S. energy bill rider, extending Daylight-SavingTime by three weeks in the spring, and a week in the fall(switching into DST on the second Sunday of March, rather than thefirst Sunday of April as it currently is, and switching back toStandard time on the first Sunday of November rather than the lastSunday in October).

Given that many don’t entirely understand DST, I thought I’dshare a graph I made some time back (I originally planned onturning the source algorithm into a web service to allow one topunch in the inputs such as location and generate their own graph,but could never justify spending the time on it).

Toronto Sunrise/Sunset DST

All values are calculated for Toronto, Ontario, for2005. The red line represents EST sunrise, the yellow EST solarnoon, while the cyan line represents EST sunset. The purple linesrepresent the 9-5 workday, adjusted in the summer months to accountfor DST (where 9-5 is really 8-4). The blue lines represent theextensions brought about by this change (3-weeks earlier in thespring, one week later in the fall). To recap – only theworkday period on the graph above calculates in DST (e.g. the 8pmsunset during the summer is 9pm on the clock during DST, and the4:20am sunrise is actually 5:20am on the clock).

As much as I dislike the incredibly costlyconfusion and complexity of DST (my two and a half year old stillhasn’t adjusted), there is a small amount of logic behind it -Presuming that human beings don’t naturally adapt to the sun comingup earlier during the summer, DST moves an hour of this presumablyunused time into the traditional post-work hours, “lengthening” theevening (not really lengthening the evening, butartificially doing so by moving the traditional 1950s work hoursearlier in the day).

Many people would argue against this, saying thatthe summer hours give them an opportunity to jog, garden, go to thegym, and otherwise take advantage of the extended pre-work hours.Nonetheless, DST is geared towards those who do nothing untiltheir pre-work preparation (e.g. the alarm clock goes off an hourand 30 minutes before the work day starts). For those people DST isentirely beneficial.

Extrapolate that logic out,though, and there should be a second layer of DST thatmoves the clock yet another hour forward during May to September.Maybe an hour more during June. Perhaps we should have a dynamicclock, such that 9am is an hour after sunrise year round.

Humor aside, there is a tremendousrisk of this DST extension, especially coming into force soquickly. Having worked with a number of daylight-saving timerelated software problems (please use UTC people, or atthe very least disregard DST), I would wager that there will besignificant ramifications of this. Millions of dollarswill need to be spent preparing for, and then cleaning up after,what many seem to think is a simple date change.

Anyone interested in the source data that Igenerated for this can find it here (it’sa Microsoft Excel worksheet).