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Which saves more energy, turning off the lights or leaving them on a short while? by Robin Green
Which is better, leaving the light on when you step out of a room for a short time, or turning it off?
If you're into energy conservation, or trying to cut your home energy bills, you have probably asked yourself this question. And chances are you have accepted the conventional wisdom, that it is better to leave the light on for short periods, than turn it off, then on again.
In this case, what we take for granted is just plain wrong.
The story goes like this: When you turn on a lightbulb, it consumes five minutes (or 15 - take your pick) of what the light normally uses, within that first second. So if a four-year-old switches the light on and off for a whole minute, once per second (30 times on per minute), they would actually be using 5 minutes of electricity times 30, or 150 minutes of power within that 60 seconds.
It's not hard to demonstrate that this is nonsense. Suppose the kid is toggling a 100 watt light. Over the course of sixty seconds, if we accept that switching on the light on uses the equivalent of what the light normally uses in five minutes, we have used 100 watts times 150 minutes.
Now, 150 minutes worth of electricity at 100 watts is the same amount of power as 1 minute of electricity at 15,000 watts. And since the light was turned on and off over the course of one minute, it means that if our assumption about the size of the initial power surge is correct, during that one minute the light bulb behaved as if it were burning 15,000 watts continuously.
Remember your high school physics class, where you learned the rule: Watts = Amps X Volts? In this case, we know both the Volts and the Watts so we can fill in:
15,000 (Watts) = Amps X 110 (Volts)
(I am assuming the toddler lives in the Americas, where voltage is typically 110). To resolve Amps, we can divide both sides by 110 so we get:
15,000 / 110 = Amps
Which means that the light was drawing 136 amps of power.
Now I don't know about your house, but mine is certainly not going to be able to handle a 136 amp current on one light for a whole minute, since the whole house has a power supply of just 100 amps. And my circuit breakers are all 15 or 30 amp breakers - which means they trip off when the power surges to much more than their rated amperage of 15 or 30 amps. So that toddler turning the light on every other second for a minute, yielding a 136 amp draw, would blow the circuit breaker for the circuit the light is on, and possibly blow the main circuit breaker for the house.
It is true that there is a power surge when you power a light bulb on. But the surge is for less than a second - it is actually a tiny fraction of a second. And the amount of the surge is far smaller than the touted 5 minutes of normal use of the light.
Fine, but what about burning out the bulb? Doesn't turning it on and off too many times wear it out?
Yes, it will burn out faster. I've seen my own kids blow a light bulb with the on-off trick - especially if they do it repeatedly for a minute or more, and the bulb was old to start with.
But that bulb the kid burns out was probably a bit old to begin with, and there have probably been many times the kid played the flick switch without burning out the bulb. And even if you assume that each flick of the switch reduces the bulb's life by one hour (it's probably nowhere near that much), you'll still cut your energy consumption if you switch the lights off whenever you step out of the room.
Again, consider the lowly incandescent. You can buy a cheap 100 watt bulb for around 25 cents and it lasts about 1,000 hours. They burn 0.1 kilowatt hours each hour they are on. If we assume we burn a bulb out in 1,000 on-off cycles, and electricity costs us 10 cents a kilowatt hour, that means it costs us 1 cent to run the bulb for one hour (100 watts = 0.1 kilowatt, X 10 cents = 1 cent).
So, each time the light gets switched off (which entails switching it back on later) you are spending a thousandth of the 25 cents you spent on the bulb, or one twentieth of a cent (a mere $0.0005!)
And every time you turn a bulb off for five minutes you are saving 5/60 of the $0.01 it costs to run the bulb for an hour, or 0.08 of a cent.
So switching the light off for five minutes cuts your electricity costs by more than three times the extra you'll be spending on shortened bulb life. And remember, we assumed that each flick of the switch uses an hour of the bulb's life, but it's probably far less than that - we just chose an hour to prove the point.
There is one other flaw with the leave-the-light-on conventional wisdom: it fails to take into account what happens when we get distracted.
You leave the room for a few minutes to put something away, but you leave the light on as you plan to return shortly. But a neighbor at the door, a friend on the phone, or some other distraction, keeps you away from the room where you left the light on - and half an hour or more, you remember that light left on. Even worse, if the light was in a room you don't visit often - the basement work room or that empty third bedroom, you might not discover the light has been left on until several days later. Forgetting to turn a light off in one case like that can eat up way more money and energy than shortening the bulb's life by an hour.
So remember to turn that light off when you lave a room. You'll save energy and your hard-earned cash. Even better, this first small step you take will remind you to take more ambitious steps to save energy, and can inspire your family, friends and neighbors to turn off the lights too.
Robin Green runs Green-Energy-Efficient-Homes.com, a website that helps you save energy in your home. There you'll find free ideas on energy efficient lighting as well as more on turning off lights to save energy. You'll also find a CFL savings calculator you can use to determine when it makes economic sense to upgrade an incandescent light bulb to a compact fluorescent bulb.
Article Source: http://www.earticlesonline.com/Article/Which-saves-more-energy--turning-off-the-lights-or-leaving-them-on-a-short-while-/482479
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