Dimmer Switch = Energy Savings ??

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  #1  
Old 03-07-06, 09:39 AM
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Dimmer Switch = Energy Savings ??

If you use a dimmer switch to lower a lights intensity... does the Amp draw on that supply circuit also deminish?
 
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  #2  
Old 03-07-06, 09:53 AM
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Originally Posted by DIY-Steve
If you use a dimmer switch to lower a lights intensity... does the Amp draw on that supply circuit also deminish?
Yes, it has to when you think about it a little more. The dimmer puts a resistance in series with your incandescent (also a resistor). Since they are in series, the overall resistance increases, decreasing supply voltage and, therefore, overall current (amperage.) This is why the lamp glows with less light.

Good question.

A higher wattage (brighter) lamp has a filament with a lower resitance, which passes a higher current, so has a brighter light, but at the cost of more power (same voltage x more current).

A dimmer lowers the supply voltage (which pushes fewer amps) but keeps the load resistance (lamp) the same.
 

Last edited by MAC702; 03-07-06 at 10:14 AM.
  #3  
Old 03-07-06, 10:07 AM
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Thanks for the speedy response.

I thought this may be the case... but, was also confused about the newer electronic dimmers.

As far as I know (which isn't a lot when you talk the inner workings of these things), the newer light dimmers use their electronics (black box to me) to dim the light vs. a variable resister in the older style dimmer... does this matter when you talk about energy savings?

Thanks again,

Steve
 
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Old 03-07-06, 12:45 PM
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Originally Posted by DIY-Steve
the newer light dimmers use their electronics (black box to me) to dim the light vs. a variable resister in the older style dimmer... does this matter when you talk about energy savings?
Yes, electronic dimmers are more efficient than resistive dimmers. Quite simply, electronic dimmers switch the light on and off many times per second. Because of the carry-over glow of the filament inside the bulb, a person does not notice this very fast flicker. The effect is that the light is on for example 60% of the time and off 40% of the time which appears as if the light is 60% as bright. This also saves roughly 40% of the energy the bulb would have used.

Old style resistive dimmers put a resistor in series with with the bulb so that the voltage across the filament is 60% of normal which results in a dimmer bulb. The remaining energy is released from the dimmer in the form of heat, which wastes energy.
 
  #5  
Old 03-07-06, 12:54 PM
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When were resistive dimmers last in common residential use? My earliest memories are of electronic dimmers...

Actually even without a dimmer the current through the filament goes to zero twice per cycle (180 Hz). Because an incandescent filament responds so slowly you can't see the flicker. Faster responding gas-discharge type lamps (like flourescent) can respond much more quickly, which is why you sometimes see a stroboscopic effect when watching a fast-moving object under such light.
 
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Old 03-07-06, 08:30 PM
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> current through the filament goes to zero twice per cycle
Correct: 120 times per second.

> (180 Hz).

No, that is 60 Hz (120 half-cycles per second).



Although any dimmer reduces electric use, none can compare to actually using a lower wattage bulb or better yet, fluorescent bulbs.

A dim bulb is a very inefficient way to produce light.

If you can leave the light completely off, that's usually the best.
 
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Old 03-07-06, 08:59 PM
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Apologies if this is too far off-topic.

I think you would see more savings from replacing bulbs less often. I've noticed that bulbs I put dimmers on don't seem to burn out nearly as much as those with regular toggle switches. I've guessed that this is because the decaying filament is not "shocked" by the inrush when turned on, but I haven't got a clue about the physics end.

Check out CF dimmables such as LiteTronics MicroBrite, which will never pay for themselves, but work pretty well with standard dimmers.
 
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Old 03-07-06, 10:44 PM
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> I think you would see more savings from replacing bulbs less often.

I "fixed" an almost unreachable light over a stairway for an older man.
I wired the two bulbs in series, put in two 100W bulbs.
It makes yellow-orangish light (about 30W, I suppose), but last I knew, after many (15+?) years he still has never had to change the bulbs, versus about once a year before that.

130V bulbs produce a similar effect though not as nearly pronounced.
In San Franscisco there was a bulb that had been burning dimly at a fire station for 100 years continuously.
 
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Old 03-08-06, 03:32 AM
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As a slight counterpoint:

If you use a dimmer, you will reduce the power consumption of the lamp. You will also increase the life of the lamp.

However operating an incandescent lamp at reduced power will greatly reduce the _efficiency_ with which light is produced.

If you drop the effective voltage supplied to the lamp by 10%, the power consumption will go down by about 15%, but the light output will go down by about 30%. See the bottom of this page http://en.wikipedia.org/wiki/Halogen_lamp

-Jon
 
  #10  
Old 03-08-06, 04:36 AM
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Originally Posted by bolide
> current through the filament goes to zero twice per cycle
Correct: 120 times per second.

> (180 Hz).

No, that is 60 Hz (120 half-cycles per second).
What, you never heard of 90 Hz power ? That's what I get for trying to multiply without a calculator . Actually, I deal with third harmonics so often that I autamatically multiply by three...

Originally Posted by bolide
>If you can leave the light completely off, that's usually the best.
There's something almost zen-like in this statement...
 
  #11  
Old 03-08-06, 05:05 AM
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Nice to see that my 30W estimate was right on target.
I didn't know that my setup theoretically extended the bulb life to 7000 years! Sort of makes me feel like a Zen master.
Perhaps I should have paired a 60W with a 100W.
 
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Old 03-08-06, 06:17 AM
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In case anyone is interested in seeing a live webcam of the light which has been burning for 100 years+ I have attached a link to the site.

http://www.centennialbulb.org/photos.htm
 
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Old 03-08-06, 09:01 AM
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Info I've read says that if you reduce the light output by 50%, you reduce the power usage by 40%.

I don't think resistive dimmers have been sold for the last 20 or 30 years at least.

I get a tremendous increase in bulb life for those bulbs I have on a dimmer.
 
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Old 03-08-06, 09:02 AM
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Originally Posted by shaun4912
In case anyone is interested in ... the light which has been burning for 100 years+...
Thanks for that link. It was interesting. Sort of on topic, too, because I read the fact sheet on it and was surprised to learn that it had been MOVED twice, including as recently as 1976. So, did it get shut off for the move? Seems like that was a dangerous move for a record holder...
 
  #15  
Old 03-08-06, 10:54 AM
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Originally Posted by DIY-Steve
... does the Amp draw on that supply circuit also deminish?
With resistive dimmer, the amps from source will stay the same because the rheosat or potentiometer is just redirecting the power. So 100 watts still equals 100 watts.
To save power then the electronic dimmer can be used where the lights duty cycle is decreased.
That is that it turns on and off to save power. It is a very fast process.
 
  #16  
Old 03-08-06, 02:43 PM
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Thumbs down

Originally Posted by frankiee
With resistive dimmer, the amps from source will stay the same because the rheosat or potentiometer is just redirecting the power.
Do you have any authoritative source to back up this little piece of nonsense?

Sure a rheostat converts electrical energy to heat.

But total power consumed by the circuit decreases. Power is not diverted.

I can prove this because a rheostat has no neutral connection.
All current that passes through it goes to the light bulb too (it is 100% in series).
 
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Old 03-08-06, 03:44 PM
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Originally Posted by frankiee
With resistive dimmer, the amps from source will stay the same because the rheosat or potentiometer is just redirecting the power.
Wrong. Go back and read Post #2.
 
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