Thursday, January 13th, 2011

How Daylight Saving Works

To start with daylight saving doesn’t actually add any daylight hours to the day and so all those stories about fading curtains and so on are nothing more than stories. What daylight saving does is to move the daylight hours so that they represent a slightly different part of the day.

Consider the situation in the morning when you get up. It is either still dark or there is daylight. Similarly when you go to bed it is either still daylight or it is dark. Daylight saving is only useful when one of these combinations occurs – where it is light when you get up and dark when you go to bed.

What daylight saving does is to remove an hour of daylight from the start of the day and add it to the end. So if it was light for an hour and a half before you got up and dark for three and a half hours before you go to bed it will now only be light for half an hour before you get up and dark for only two and a half hours before you go to bed. In this situation you get an extra hour of daylight when you are awake and able to use it and an hour less of daylight when you are asleep and therefore do not need it to be light.

What this also means is that the effectiveness of daylight saving varies depending on where you are. For those close to the equator the lengths of the days do not vary all that much and so there is no point in those places having daylight saving for a part of the year. Either people are always sleeping through an hour or more of daylight at the start of each day in which case going onto permanent daylight saving time will move it to when they are awake or they always wake just before it gets light and there is never a benefit to daylight saving (unless it relates to maintaining the same timezone as their neighbours immediately to their north or south).

For those close to the poles the length of the day will vary so much that in winter they will always get up in the dark and go to bed in the dark while in summer they will always get up in daylight and still be in daylight when they go to bed. For these people too there is no benefit to daylight saving.The areas where this occurs though are fairly sparsely populated.

So (with the exception of those living really close to the poles) the further away from the equator the more likely that a place is to benefit from daylight saving time moving an hour from the time that people are sleeping to the time when they are awake and so the more likely that they will support daylight saving while their neighbours nearer the equator would probably prefer that they didn’t use daylight saving as there is nothing in it for them (except for their ending up in different timezones if they don’t apply it).

Of course you could achieve the same result for yourself simply by getting up at dawn every day and so maximising the number of daylight hours that you have. The problem with this though is that unless everyone gets up earlier you will not be able to interact with everyone else consistently. The only way to add this consistency is to get everyone to change their clocks so that they read the same time for everyone and everyone gets up that hour earlier.

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