Thursday, April 8th, 2010

Daylight Saving Time

Daylight saving ended here last weekend so this seems like a reasonable time to consider the situation with regards to why some places have daylight saving and others don’t and the problems that can cause for people travelling between those places.

The first thing to realise is that the further away from the equator that a place is the more effective that daylight saving will be. That’s because places close to the equator do not have their days vary greatly in length. If a day in mid summer is only an hour or so longer than a day in mid winter then shifting the clocks an hour will not achieve anything since people will be awake for about as much time when it is dark regardless and it is only when the time is changed to move people’s waking hours to correspond to when it is daylight that any saving is achieved.

Places distant from the equator will have their days much longer in summer than they are in winter. If it gets light at 4am and gets dark at 8pm then the first few hours of daylight are wasted by most people who are still in bed asleep at that time and those same people will still be awake doing things after dark. Shift the clocks by an hour and now it gets light at 5am and gets dark at 9pm and you have increased the amount of time that most people will be awake while it is daylight and reduced the time they are awake in the dark. That’s how daylight saving reduces the amount of power required – by moving more of the daylight hours into the period of the day when people are awake.

One problem that daylight saving creates in Australia is where the southern states that actually benefit from daylight saving switch to daylight saving time while the northern states that are normally in the same time zone do not. The only benefit that those northern states could achieve by going on to daylight saving time would be to keep in the same time as their southern neighbours since the length of the day there doesn’t vary enough to make it worth having for what it is supposed to achieve. Of course the same situation applies in some northern countries where those places to the south do not gain any local benefit from having daylight saving time.

The other issue with daylight saving time which isn’t properly considered is the appropriate time to start and end daylight saving. Since its purpose is to move an hour of daylight from early morning when most people are asleep to later in the day when they are awake it achieves nothing when people both wake in the dark and go to sleep in the dark. The appropriate time for starting daylight saving is when it starts getting light well before most people are awake so that those people will actually get the extra hour of daylight.

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One Response to “Daylight Saving Time”

Antonia Liedberg Says:

I was reading your blog and thought i would say hi.