Electrcal use of Light Bulbs
Did You Leave The Lights On?
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, the conventional wisdom is dead wrong.
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Here is how the argument goes:
When you first power a light on, it will use as much as five (or fifteen) minutes of the regular cost. That works out to 30 x 5 minutes, or 150 minutes, worth of electricity in that one minute.
Let’s assume the toddler is turning on and off a 100 watt bulb. Over the course of that one minute, if we assume that turning the bulb on uses 5 minutes worth of the typical consumption of the bulb, we have used 150 minutes worth of electricity at 100 watts.
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.
If you studied electricity at all in high school, you probably remember the formula: Watts = Amps X Volts. In this case, we know both the Watts and the Volts so we can take this equation:
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 watts / 110 volts = Amps
Which means that the light was drawing 136 amps of power.
Now I’m not sure about your electrical service, but mine is a 100 amp service, which means that light is going to blow not only the 15 or 30 amp circuit breaker it’s on, but the main breaker for the whole house.
You can’t, after all, send 136 amps of power through a 100 amp power supply for longer than a fraction of a second. So that kid switching the bulb on and off sxity times in a minute would either blow the breaker for the room where the light is, or for the whole house, in fairly short order.
So what’s the scoop? Yes, there is a power surge when a light is turned on. But that surge lasts only a tiny fraction of a second, and it works out to far less energy than the usually quoted five or fifteen minutes of leaving the light on.
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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.
Let’s consider that 100-watt bulb again, which costs as little as a quarter these days, and lasts 900 to a thousand hours. They burn 0.1 kwh for every hour you leave them on. Assuming that a thousand on-off cycles destroys the bulb, and assuming we pay ten cents per kwh for our electricity, it’s going to cost us one cent to run the bulb for an hour (100 watts for an hour is 0.1 kwh, at ten cents per kwh means one cent).
So, every time you turn a bulb off (which means you will later have to turn it on) you are using 1/1000 of the $0.25 you paid for the bulb, or 0.05 of a cent (that’s $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 you actually save over three times as much by turning the light off for five minutes, as you would by extending the bulb life by leaving it on. And my assumption that it takes an hour of the life of the bulb each time you turn it on is probably a big over-estimate. It was just to prove a point.
There’s one other problem with the argument that it’s better to leave the light on for a short time. It doesn’t consider what happens when we forget we’ve left the light on.
You step out of a room for a couple of minutes to do something else, and you leave the light on because you know you will be back soon. But you get distracted - a knock at the door, a phone call, you suddenly remember an errand you have to run - and half an hour or several hours later, you discover the light you had left on.
The worst is when the light is in a seldom-used room - furnace room or a guest bedroom - and you don’t remember to go back and turn the light off. Days later you discover it is still on. One distraction like that canl cost you far more than the cost of one hour of the operating life of the bulb.
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.
By: Robin from Green Energy Efficient Homes
Article Directory: http://www.articledashboard.com
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.
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Tags: Electrical consumption, electricity savings, light bulbs, save on light bulbs
April 2nd, 2009 at 10:03 am
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