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# Do dimmers save electricity?

#1
01-16-05, 07:58 PM
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Join Date: Jan 2005
Location: USA
Posts: 605
Do dimmers save electricity?

Do dimmers save electricity when dimmed? How do they actually function?

For example: a 100 watt bulb uses 100 watts/hour on a regular on/off switched circuit. If that switch is changed to a dimmer and adjusted to 50% does the electricity usage drop to about 50 watts or not?

Also, some bulbs buzz at dimmed levels - is there a way to eliminate the buzz? Are certain types of bulbs (or circuits) more prone to buzz when dimmed?

Thanks!

#2
01-16-05, 11:15 PM
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Join Date: Aug 2004
Location: USA
Posts: 539
Not an electrical expert, but

I'll give it my best shot.

A dimmer set at 50% with a 100Watt light bulb doesn't quite save you 50 watts of power, due to losses in the dimmer, part of the electricity becomes heat. I think that I'd be pretty close though, say 40-45 watts saved (maybe higher if the dimmer is very efficient).

A dimmer works by: (from this link: http://home.howstuffworks.com/dimmer-switch2.htm) "The switching cycle is built around the fluctuation of household alternating current (AC). AC current has varying voltage polarity -- in an undulating sine wave, it fluctuates from a positive voltage to a negative voltage. To put it another way, the moving charge that makes up AC current is constantly changing direction. In the United States, it goes through one cycle (moving one way, then the other) 60 times a second. The diagram below shows this sixtieth-of-a-second cycle. A modern dimmer switch "chops up" the sine wave. It automatically shuts the light bulb circuit off every time the current reverses direction -- that is, whenever there is zero voltage running through the circuit. This happens twice per cycle, or 120 times a second. It turns the light circuit back on when the voltage climbs back up to a certain level.
This "turn-on value" is based on the position of the dimmer switch's knob or slider. If the dimmer is turned to a brighter setting, it will switch on very quickly after cutting off. The circuit is turned on for most of the cycle, so it supplies more energy per second to the light bulb. If the dimmer is set for lower light, it will wait until later in the cycle to turn back on.
That's the basic concept, but how does the dimmer actually do all of this? In the next couple of sections, we'll look at the simple circuitry that makes it work."

You can try different brands of light bulbs, some are more prone to buzzing than others. Depending on the wattage and type of lamp, you could try a "rough service" type light bulb....ceiling fan bulb, garage door opener bulb, etc. These tend to have thicker and better supported filaments in the bulb that may make them less noisy.
If it's the buzz is really loud, try checking the electrical connections at the light fixture and dimmer....sometimes a slightly loose connection may buzz. My last idea would be to try a different brand of dimmer, some will be worse than others.

I hope this helped and that I'm not too far off-base here!

#3
01-17-05, 11:35 AM
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Join Date: Jul 2003
Posts: 54
Will hooking up a fluoresent bulb to a dimmer damage the bulb even if turned all the way on?

Mr Bill

#4
01-17-05, 12:33 PM
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Join Date: Aug 2002
Posts: 225
I think dimmers are for incandescent bulbs only as flourescent light are either ON or OFF and incandescent can vary from ON or OFF. Kinda like didgital vs. analog...

#5
01-17-05, 01:04 PM
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Join Date: Jul 2003
Posts: 54
I would like to replace 6 r-30 floodlamps with fluorescents.
I am having a power struggle with the wife on this.
I want to at least change out the present bulbs and check out the quality/quantity of light. If I have to change out the dimmer switch I will
but only if the dimmer switch, while turned fully on, would cause problems.

Mr Bill

#6
01-17-05, 06:11 PM
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Join Date: Jan 2005
Location: USA
Posts: 605

#7
01-17-05, 09:59 PM
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Join Date: Aug 2004
Location: USA
Posts: 539
In order to dim a

flourescent fixture, 1) the fixture must be designed to be dimmed and 2) you need a special flourescent dimmer. I think it's kind of the same idea why you don't put a standard dimmer on a low-voltage fixture.....you'll damage something expensive!

Hope this helps!

#8
01-18-05, 03:25 AM
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Join Date: Jul 2003
Posts: 54
When a regular dimmer (Lutron brand) is fully on is it still "processing"
the AC line or does it bypass the electronics giving a pure sine wave?

mrbill5

#9
01-20-05, 08:12 PM
Member
Join Date: Mar 2004
Posts: 137
Originally Posted by mrbill5
When a regular dimmer (Lutron brand) is fully on is it still "processing"
the AC line or does it bypass the electronics giving a pure sine wave?

mrbill5

the triac inside the dimmer (the device doing the dimming) is still working, it is just switching fast enough to give the appearance of an almost complete pass through

#10
01-20-05, 08:14 PM
Member
Join Date: Mar 2004
Posts: 137
Originally Posted by mrbill5
I would like to replace 6 r-30 floodlamps with fluorescents.
I am having a power struggle with the wife on this.
I want to at least change out the present bulbs and check out the quality/quantity of light. If I have to change out the dimmer switch I will
but only if the dimmer switch, while turned fully on, would cause problems.

Mr Bill

In order to dim fluorescents, you not only need a dimmer that is for fluorescent, but you need to change from a switching ballast to a dimming ballast, the tombstones on the fixture are most likely instart and you need rapid start, in addition to the wiring of a dimming ballast is different from a switching ballast.

lastly, depending on the ballast chosen, you may need an additional wire in your wall between the fixture and the wallbox as many ballasts are of a 3 wire type

#11
01-20-05, 08:23 PM
Member
Join Date: Mar 2004
Posts: 137
Originally Posted by Desy2820
I'll give it my best shot.

A dimmer set at 50% with a 100Watt light bulb doesn't quite save you 50 watts of power, due to losses in the dimmer, part of the electricity becomes heat. I think that I'd be pretty close though, say 40-45 watts saved (maybe higher if the dimmer is very efficient).

A dimmer works by: (from this link: http://home.howstuffworks.com/dimmer-switch2.htm) "The switching cycle is built around the fluctuation of household alternating current (AC). AC current has varying voltage polarity -- in an undulating sine wave, it fluctuates from a positive voltage to a negative voltage. To put it another way, the moving charge that makes up AC current is constantly changing direction. In the United States, it goes through one cycle (moving one way, then the other) 60 times a second. The diagram below shows this sixtieth-of-a-second cycle. A modern dimmer switch "chops up" the sine wave. It automatically shuts the light bulb circuit off every time the current reverses direction -- that is, whenever there is zero voltage running through the circuit. This happens twice per cycle, or 120 times a second. It turns the light circuit back on when the voltage climbs back up to a certain level.
This "turn-on value" is based on the position of the dimmer switch's knob or slider. If the dimmer is turned to a brighter setting, it will switch on very quickly after cutting off. The circuit is turned on for most of the cycle, so it supplies more energy per second to the light bulb. If the dimmer is set for lower light, it will wait until later in the cycle to turn back on.
That's the basic concept, but how does the dimmer actually do all of this? In the next couple of sections, we'll look at the simple circuitry that makes it work."

You can try different brands of light bulbs, some are more prone to buzzing than others. Depending on the wattage and type of lamp, you could try a "rough service" type light bulb....ceiling fan bulb, garage door opener bulb, etc. These tend to have thicker and better supported filaments in the bulb that may make them less noisy.
If it's the buzz is really loud, try checking the electrical connections at the light fixture and dimmer....sometimes a slightly loose connection may buzz. My last idea would be to try a different brand of dimmer, some will be worse than others.

I hope this helped and that I'm not too far off-base here!
great explanation.

In simple terms, your lights right now as they are are turning on and off 120 times a second (60hz) becasue they switch so fast your eyes can not adjust to this but they is definately 120 moments that no power is being applied. What a dimmer does is holds this off time for a greater amount of time without affecting the total cycle time. so the lights still go on and off 120 times a second but now with the off time being held a bit longer. this means the on time is now a bit shorter. and the way you see it - it is dimmed.

now if you are extendign the amount of time that no voltage is being applied, when there is no voltage, there is no electricity being consumed, and so no power at that given time is being used as well.

as a general rule , lights dimmed 10% =10% electricity saved
dimmed 25%= 20% electricity saved
dimmed 50% = 40% electricity saved
dimmed 75% = 60% electricity saved

oh and about the buzzing from the lamps use either

GE - XL Ultra
Sylvania - Daylight Plus
Phillips - Halogena

These bulbs are designed to last 3000Hrs and so the filament supports are stronger and fastened better to the filament and base. this will eliminate the filament from vibrating which is the cause of lamp buzz. and these bulbs are designed with dimming in mind.

If you will now excuse me, I must go soak my typing fingers in ice and I believe there are about to bleed

#12
01-21-05, 02:53 AM
Member
Join Date: Jul 2003
Posts: 54
thanks
I bought a good old regular single pole switch and will change out the dimmer.
We always ran the incandescents at 100% so it was a no-brainer.

mr bill

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