OT: Question For Electrical Engineer Types....

[Blaine]

Does a light dimmer use less electric when you dim the lights, or does the same amount get used and it just gets drained away someplace besides the lightbulb? I have a bet on this one. Nope, ain't gonna say...already looked dumb enough this week

[Ben_Rumson]

ARE YOU TALKING A BOUT A LAMPSHADE OR WHAT?...

[awp101]

If I remember my Basic Electricity stuff, the dimmer is a potentiometer. The amount of incoming power remains the same but the power coming out (and therefore to the bulb) can be less depending on the switch setting. The remaining voltage is "stored" as "potential" but you still have 120V (or whatever the power source is) coming into the switch.

That is, IIRC. Clear as mud?

[Noah Zark]

Conventional dimmer switches for incandescent lamps are variable resistors. When the dimmer is adjusted "high," there is little or no resistance in the circuit and the lamp burns bright. When the dimmer is adjusted to dim the lamp, it does so by increasing the electrical resistance in the circuit and converting some of the current to heat in the dimmer switch itself. Sorry, Andrew, the energy is not "stored."

So no, you don't use less energy when the lamp is dimmed, because some of that energy is being converted to heat, dropping voltage to the lamp. V=IR and all. But the lamp doesn't glow as bright and thus doesn't get as hot and lasts longer when dimmed.

DO NOT use compact fluorescent lamps on dimmer circuits.

Noah

[pokey]

ARE YOU TALKING A BOUT A LAMPSHADE OR WHAT?...

[Blaine]

Variable resistance....that makes real good sense....thanks! I was hoping it was like a throttle valve and only let in so much at a time

[Old No7]

"DO NOT use compact fluorescent lamps on dimmer circuits."

Actually... Some of the newer CFLs (pronounced as "see-fulls") or Compact Fluorescent Lights ARE labeled as being dimable. We have on in the dining room and it works slick, on the same dimmer we had before. But not all CFLs are, so you do need to be careful.

(Used to work for Sylvania for 18 years... But then I saw the light [pun fully intended!] and 3 years after I left for a better job/industry, they closed the plant down and moved 220+ jobs to Mexico and the Czech Republic...)

Old No7

[AJMD429]

Just using some pretend numbers to illustrate, if you have a 100 volt battery or other direct current power source, and the bulb alone has a resistance of 20 ohms, the force of that 100 volt 'push' across the 20 ohms resistance would allow 5 amps of current to flow. If on the other hand, you add a resistor of 30 ohms in series with the bulb, the total resistance is 50 ohms, which would allow only 2 amps of current to flow. There would be 100 volts of potential or 'push' across the resistor and bulb combination, but the bulb has 20/50th's of the resistance, so would have effectively 40 volts across its 20 ohms, so it would allow 2 amps to flow (and it would glow less brightly), and the resistor would have effectively 60 volts across its 30 ohms, the 'same' 2 amps flowing in series through it.

In the bulb-only case the 5 amps is a faster electron flow, and would drain a battery faster, and IS using more energy. The 2 amp situation would allow the battery to last longer, since it is a slower electron flow, and uses less energy.

It is true that the resistor 'consumes' some of the energy and puts it out as heat, but the slowing of the overall flow of electrons is greater.

If you did the same 'experiment' and used a second bulb, with a filament of 30 ohms resistance, the energy outcome would be the same, only with light vs. heat as the 'second' energy output. Theoretically, the light output would still be less, I think, since the total of 2 amps through those two bulbs would be less energy flow than the 5 amps through one bulb - at least I think that is the case. Likewise, if you switched from the 20-ohm bulb to a single 50-ohm one, you'd save energy, as the electrons would not flow through that filament as fast (and all else being equal you'd get less light output).

Anyway, that's how I remember it from physics classes, and my ham license studying...

[awp101]

Conventional dimmer switches for incandescent lamps are variable resistors. When the dimmer is adjusted "high," there is little or no resistance in the circuit and the lamp burns bright. When the dimmer is adjusted to dim the lamp, it does so by increasing the electrical resistance in the circuit and converting some of the current to heat in the dimmer switch itself. Sorry, Andrew, the energy is not "stored."

It's been too long since I had to explain it and I couldn't think of how to describe what happens to the excess. "Stored" was the only thing that came to mind...

[Winnetou]

Although the knob or slider on a lamp dimmer controls a potentiometer (variable resistor with terminals at both ends), this resistance does not directly control the power to the lamp. Mains electricity is alternating current, of an essentially sinusoidal waveform. Thus, the voltage rises from zero to positive, declines to zero, descends to negative, and rises again to zero—at the rate of sixty complete cycles per second in the U.S.

The dimmer uses a bi-directional solid-state switching device called a TRIAC to control the power to the lamp. The TRIAC is triggered by the alternating current waveform, and turns on during a part of each half-cycle. By changing the amount of each half-cycle for which the TRIAC is turned on, the overall power to the light bulb is varied. The shorter the “on” period, the dimmer the lamp. The thermal inertia of the bulb’s filament prevents the light from flickering visibly from the alternating current, or from the on-off cycles of the TRIAC.

This type of power control is called duty cycle control, and lamp dimmers have been made on this principle since the 1960s.

To answer the initial question, the lower the light setting, the less power consumed. In fact, a lamp dimmer is far more efficient than direct control by a variable resistor, since it dissipates much less energy as heat.

Before the era of modern lamp dimmers, variable inductances (“chokes”) were sometimes used in preference to variable resistors, especially for high-power lamps, since the former impeded the flow of alternating current without dissipating appreciable energy as heat. In direct current systems of the past, variable resistors were the only viable option; but for a long time, residential dimmers were of this kind for alternating current as well, because the construction was light and inexpensive.

[Noah Zark]

. . . The dimmer uses a bi-directional solid-state switching device called a TRIAC to control the power to the lamp . . . This type of power control is called duty cycle control, and lamp dimmers have been made on this principle since the 1960s.

Modern US and Canadian and probably European dimmers are Triac-based. We recently tested dimmers from China, and they were most definitely not Triacs.

Noah

[GoatGuy]

Huh....

[Rimfire McNutjob]

Both methods can lower the overall power consumption, but the Triac will do so far more efficiently as was previously stated. If you really want to drop your usage for lighting purposes, move to LED based lamps.

Using a Triac incurs losses due to the voltage drop across the semiconductor ... usually only a few volts, maybe less.

Using a variable resistor incurs losses as a result of the resistance to current flow and the commensurate voltage drop.

Both result in extra heat dissipation at the controlling device.

[Blaine]

Alllllllrighty, then......dimmers let you use less power?

[awp101]

Wait, you want a yes or no answer from engineers?

[Blaine]

Wait, you want a yes or no answer from engineers?

I forgot.......I worked with ThinFilms engineers at a semi-conducter Fab for a couple years.....It is impossible for one to give you a yes, or no. In engineering, simple solutions to complex problems are not tolerated.

[olyinaz]

Yes Blaine, dimmers let you use less electricity if you choose. There is some loss, and I think that's what the engineers were getting at, but overall you should be drawing less electricity from your system provided you dim the light enough to make a change in visible output.

Anybody else here make the mistake of putting a lamp dimmer on a ceiling fan?

Oly

[Noah Zark]

Alllllllrighty, then......dimmers let you use less power?

Nothing that will translate into a lower monthly electric bill.

If a lower monthly bill is your goal, then forget dimmers and switch out your bulbs to Compact Fluorescents or the newer LED bulbs. Payback will be 1-3 yrs depending on the type of bulb you purchase.

Noah

[Noah Zark]

. . . Used to work for Sylvania for 18 years... But then I saw the light [pun fully intended!] and 3 years after I left for a better job/industry, they closed the plant down and moved 220+ jobs to Mexico and the Czech Republic . . .

I live only a few miles from the Osram/Sylvania plant in St. Marys, PA and about 25 miles from the old Sylvania plant in Emporium. That one probably shut down before your time.

I buy only Osram/Sylvania lamps with the "St Marys, PA" address on the packaging whenever possible. Gotta keep friends, neighbors, and fellow church members employed.

Noah

[Blaine]

Alllllllrighty, then......dimmers let you use less power?

Nothing that will translate into a lower monthly electric bill.

If a lower monthly bill is your goal, then forget dimmers and switch out your bulbs to Compact Fluorescents or the newer LED bulbs. Payback will be 1-3 yrs depending on the type of bulb you purchase.

Noah

That was never the intent, but I would use a 7 Watt night bulb instead of a dimmed 100 Watt if it was a huge difference. I do use the Compact Fluorescents, and find they don't last NEAR as long as they claim, however, about once a year, the local utilities will get a grant to sell them for about a buck apiece and I'll stock up for the year.

[Noah Zark]

. . . I do use the Compact Fluorescents, and find they don't last NEAR as long as they claim . . .

When your CFs die, is it in a cloud of noxious white/tan smoke, with much sputtering and blinking, and even some sparking?

I've trained myself to IMMEDIATELY hit the switch if one of those CFs starts flashing on and off. That's the (usual, but not always) first indication that it's checking out.

Noah

[Blaine]

. . . I do use the Compact Fluorescents, and find they don't last NEAR as long as they claim . . .

When your CFs die, is it in a cloud of noxious white/tan smoke, with much sputtering and blinking, and even some sparking?

I've trained myself to IMMEDIATELY hit the switch if one of those CFs starts flashing on and off. That's the (usual, but not always) first indication that it's checking out.

Noah

They do worry me some......

[Noah Zark]

. . . I do use the Compact Fluorescents, and find they don't last NEAR as long as they claim . . .

When your CFs die, is it in a cloud of noxious white/tan smoke, with much sputtering and blinking, and even some sparking?

I've trained myself to IMMEDIATELY hit the switch if one of those CFs starts flashing on and off. That's the (usual, but not always) first indication that it's checking out.

Noah

They do worry me some......

Me too. That's why no fixture on a timer has a CF in it. No CFs are lit if nobody's home.

Noah

[wecsoger]

and find they don't last NEAR as long as they claim,

CFL's do not like being turned off and on very much. (well, I guess, do any of us?//grin//) To get maximum life from a CFL, turn it on and leave it on. And have it on a backup power system and something to protect it from spikes and brownouts from the commercial mains.

Yeah, like that's going to happen.

I do have to admit, the latest CFL's are much much better now with easier-on-the-eyes color temperature and not quite as fussy about colder temperatures. The one in our outside yard light still takes a while to warm up to full light in freezing temperatures.

LEDs are where the CFLs were five or so years ago. Ghastly color temperature, price point too high for economical operation. They last a lot longer than the CFLs, don't have the warm up and mercury issues and in the long run will be what we're eventually using.

[Blaine]

When you guys talk all technical, I don't know watt you're talking about, but I get a charge out of it.

[awp101]

The fact it took this long to get around to the puns is simply revolting...

[Ben_Rumson]

Yeah.. I'm shocked!

[Noah Zark]

Yesh, I do wish people would be direct in responding, instead of alternating between being serious and facetious.

Noah

[pokey]

how enlightening.

[awp101]

Yesh, I do wish people would be direct in responding, instead of alternating between being serious and facetious.

Noah

Eh, just flow with the current. Much less stressful...

[jeepnik]

Yes Blaine, dimmers let you use less electricity if you choose. There is some loss, and I think that's what the engineers were getting at, but overall you should be drawing less electricity from your system provided you dim the light enough to make a change in visible output.

Anybody else here make the mistake of putting a lamp dimmer on a ceiling fan?

Oly

Bye Bye motor.

[Sixgun]

Geeze! You guys are way too smart and educated for me to understand all these "triacs" and "ohms". If I want to save money on electric bills, I can't figure all that stuff out--I just turn my meter upside down.

No, not really, but my Dad used to do it with the old style meters back in the old days.

Hey, does anyone know how the electric company reads these new smart meters? Since mine was installed several years ago, I have yet to see a meter reader.---------Sixgun

[madman4570]

The electronic dimmers cycle on and off so rapidly that our eyeballs and brains can't even tell the electricity was shut off in the first place. After all, imagine having a light bulb on full blast for an hour. It produces, in that time span, a given amount of light. If you were able to rapidly turn on and off the light bulb so that is was actually only on for 30 minutes of the hour, you would use half the electricity, right? That is what new dimmers do. They just do it so well you can't tell they are turning on and off!


Solid-state light dimmers work by varying the "duty cycle" (on/off time) of the full AC voltage that is applied to the lights being controlled. For example, if the voltage is applied for only half of each AC cycle, the light bulb will appear to be much less bright than when it get the full AC voltage, because it get's less power to heat the filament. Solid-state dimmers use the brightness knob setting to determine at what point in each voltage cycle to switch the light on and off.

Typical light dimmers are built using thyristors and the exact time when the thyristor is triggered relative to the zero crossings of the AC power is used to determine the power level. When the the thyristor is triggered it keeps conducting until the current passing though it goes to zero (exactly at the next zero crossing if the load is purely resistive, like light bulb). By changing the phase at which you trigger the triac you change the duty cycle and therefore the brightness of the light.

The advantage of thyristors over simple variable resistors is that they (ideally) dissipate very little power as they are either fully on or fully off. Typically thyristor causes voltage drop of 1-1.5 V when it passes the load current.

[AJMD429]

I'm glad some of you guys who understand the AC-stuff chimed in; I'm way over my head once it gets past Ohm's law.

If you really want to drop your usage for lighting purposes, move to LED based lamps.

I've always felt that the LED lamps are soon to take over household lighting, because they are

• cool-running (more energy efficient),
  lower-voltage (safer wiring),
  color/mood/ambiance-adjustable (due to multiple elements),
  last 100 times longer than most bulbs, and
  don't go out all at once (due to multiple elements)

When the recent legislation came along to 'push' us all to compact flourescents, which in my (limited, but real-world) experience, are

• still fairly hot (due to the built-in 'ballast' maybe?),
  don't last as long as claimed (maybe I just had cheap ones),
  not particularly safe (3 of maybe 100 I've used have literally caught fire), and
  not particularly environmentally-friendly (vs. regular incandescents)

...it occurs to me that perhaps the legislation was enacted primarily to give some last-minute breaths to a dying fluorescent-bulb industry, before the LED's take over much of their turf.

Does Al Gore own a bunch of Westinghouse Compact Fluorescent Bulb stock...?

[mark]

Although the knob or slider on a lamp dimmer controls a potentiometer (variable resistor with terminals at both ends), this resistance does not directly control the power to the lamp. Mains electricity is alternating current, of an essentially sinusoidal waveform. Thus, the voltage rises from zero to positive, declines to zero, descends to negative, and rises again to zero—at the rate of sixty complete cycles per second in the U.S.

The dimmer uses a bi-directional solid-state switching device called a TRIAC to control the power to the lamp. The TRIAC is triggered by the alternating current waveform, and turns on during a part of each half-cycle. By changing the amount of each half-cycle for which the TRIAC is turned on, the overall power to the light bulb is varied. The shorter the “on” period, the dimmer the lamp. The thermal inertia of the bulb’s filament prevents the light from flickering visibly from the alternating current, or from the on-off cycles of the TRIAC.

This type of power control is called duty cycle control, and lamp dimmers have been made on this principle since the 1960s.

To answer the initial question, the lower the light setting, the less power consumed. In fact, a lamp dimmer is far more efficient than direct control by a variable resistor, since it dissipates much less energy as heat.

Before the era of modern lamp dimmers, variable inductances (“chokes”) were sometimes used in preference to variable resistors, especially for high-power lamps, since the former impeded the flow of alternating current without dissipating appreciable energy as heat. In direct current systems of the past, variable resistors were the only viable option; but for a long time, residential dimmers were of this kind for alternating current as well, because the construction was light and inexpensive.

Spot on, Mark BE(Hons)

[madman4570]

With a typical dimmer switch there kinda is a rule of thumb which is--------------------
Dim your lights by a quarter, you increase your energy savings by 20 percent; dim them by half, increase your savings 40 percent. You also extend bulb life up to 20 times when you dim a bulb halfway.

[Chas.]

...of an essentially sinusoidal waveform.

That sounds like what I get up my nose when the ragweed blooms.

[madman4570]

I'm glad some of you guys who understand the AC-stuff chimed in; I'm way over my head once it gets past Ohm's law.

If you really want to drop your usage for lighting purposes, move to LED based lamps.

I've always felt that the LED lamps are soon to take over household lighting, because they are

• cool-running (more energy efficient),
  lower-voltage (safer wiring),
  color/mood/ambiance-adjustable (due to multiple elements),
  last 100 times longer than most bulbs, and
  don't go out all at once (due to multiple elements)

When the recent legislation came along to 'push' us all to compact flourescents, which in my (limited, but real-world) experience, are

• still fairly hot (due to the built-in 'ballast' maybe?),
  don't last as long as claimed (maybe I just had cheap ones),
  not particularly safe (3 of maybe 100 I've used have literally caught fire), and
  not particularly environmentally-friendly (vs. regular incandescents)

...it occurs to me that perhaps the legislation was enacted primarily to give some last-minute breaths to a dying fluorescent-bulb industry, before the LED's take over much of their turf.

Does Al Gore own a bunch of Westinghouse Compact Fluorescent Bulb stock...?

Agree the LED lights are very effcient,only issues are when actually lighting complete rooms because they are a very directional type of light, they don't create enough light to light a large area like a room "evenly" and when using numerous ones for a room for instance you have these numerous dark spots Its very apparent when measuring this effect with a light meter.(a calibrated one of course )Also many people cant tolerate that type of uneveness.Using numerous ones for that type of task also quickly dips into the cost factor as well. But absolutely they are cool technology!

[pokey]

Does Al Gore own a bunch of Westinghouse Compact Fluorescent Bulb stock...?

congratulations, i'm glad i did not have a mouthful of tea when i read that.
my first laugh out loud this morning, thanks.

[JReed]

Alllllllrighty, then......dimmers let you use less power?

Yes they use less power. While I was trying to come up with a way to explain it to you with out the use of a dry erase board the others beat me to it.

[JReed]

Yes Blaine, dimmers let you use less electricity if you choose. There is some loss, and I think that's what the engineers were getting at, but overall you should be drawing less electricity from your system provided you dim the light enough to make a change in visible output.

Anybody else here make the mistake of putting a lamp dimmer on a ceiling fan?

Oly

Bye Bye motor.

Yeah don't do that!!!!!!! The constant application and removal of power will burn it out fast. The only way to do that safely with a motor is to use a potentiometer coupled with a motor designed to run over a wide range of voltages. Don't not hook up a motor to a Triac!!!!

[SJPrice]

Yes Blaine, dimmers let you use less electricity if you choose. There is some loss, and I think that's what the engineers were getting at, but overall you should be drawing less electricity from your system provided you dim the light enough to make a change in visible output.

Anybody else here make the mistake of putting a lamp dimmer on a ceiling fan?

Oly

Bye Bye motor.

Yeah don't do that!!!!!!! The constant application and removal of power will burn it out fast. The only way to do that safely with a motor is to use a potentiometer coupled with a motor designed to run over a wide range of voltages. Don't not hook up a motor to a Triac!!!!

I hooked a motor to a Tricycle once, well it was a Briggs & Straton, so technically it was an engine albeit a small one so, never mind.