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light dimmer save energy?

light dimmer save energy?

light dimmer save energy?

does anyone know how much energy light dimmers really save when you turn them down. How do they regulate the britness anyway?

RE: light dimmer save energy?

There are several ways of making light dimmers now, but essentially they all work by reducing the voltage that gets to the light bulb. Think of an incandescent light bulb as a pure resistor. With lower voltage, a resistive load will use a reduced wattage (W = V^2/R A in a resistive load), and hence less energy. Of course, you will also get a reduced lumen output as well, but assuming you can live with less light most of the time, and only turn it up to full brightness when you absolutely need it, you will save energy.

How much? Well, how much is much? If you have a 100W bulb, and you turn the dimmer down so that it is only putting out the equivalent of a 40W light bulb, you are theoretically saving 60% of the maximum energy. If however, you can't read what you need to because it is too dim, you have actually wasted 40W of energy for no good reason! But let's say you are watching TV and just want some low ambient light, then dimming that 100W bulb makes perfect sense. Having the dimmer allows you to turn it up to full only when you want to read.

All in all however, dimmers do save energy if they are used. That 100W light bulb burning 4 hours/day, 360 days/year is 100 x 4 x 360, or 144kWH / year, which at $.05/kWH is about $7.20/year. If you dimmed it to a 40W equivalent for 80% of the time (3.2hrs/day), it would be (40 x 3.2 x 360) + (100 x .8 x 360) or about 75kWH which is $3.75/year.

So if your dimmer cost you $15.00, your payback would be 4 years, fairly reasonable, but not if you keep it turned up to full brightness all the time.

"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."   
Nikola Tesla

RE: light dimmer save energy?


Well there are those here on this very site that will tell you otherwise, but I think it's all smoke and mirrors...

Not! really, good answers will come in time...from good sources.



RE: light dimmer save energy?

But, you can just as easily install compact fluorescent bulbs, i.e., you can get the equivalent of a dimmer with more light and NO losses through the dimmer itself.  

As a general rule, you can get comparable light at around 1/3 the power consumption.


RE: light dimmer save energy?

What was smoke and mirrors about old style rheostat dimmers was the fact that they used a variable resistor to reduce the light output at the bulb. All they did was transfer some of  the energy into heat losses inside the wall box instead of light output at the bulb! When the first energy crisis hit back in the '70s, people were running around with demo boxes for dimmers with a little meter that displayed how the energy going to the light bulb was reduced, but what they didn't tell you was that the meter was hooked up downstream from the rheostat. So it didn't show the total energy in the circuit, i.e. the losse in the rheostat! Modern dimmers work differently however and they really do save energy.

"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."   
Nikola Tesla

RE: light dimmer save energy?

Thanks "jraef" you made my point.
I was attempting to get ahead of you sparky types just for the fun of it with my quippy remark,  but YOU posted ahead of me by minutes.
What I find annoying is the radio interferance that occurs  on the circuit. How do I chop that?



RE: light dimmer save energy?

In general I think most dimmers still work on some PWM principle.
I.e. you cut away energy to the bulb, by reducing the time it is connected to the power source.

The resistance in a bulb is far from constant over temperature, and the color of the emitted light has a lot to do with the temperature of the very thin wire inside the bulb.

Putting two identical 60W bulbs in series will thus not reduce the total power to 30W, but maybe to 45W.
The emitted color will, however, have shifted a lot into the red and infrared zone because of the reduced temperature.

All this means that beyond a certain dimming point the light from the bulb is of no use anymore, but it will still pull  power from the mains. More than you might think.

RE: light dimmer save energy?

From a systems perspective, dimmers are extremely inefficient.  Incandescent bulbs are barely efficient as is.  When you decrease the voltage, as described above, not only does the color shift, but you're getting even LESS light generation efficiency.

The total radiated power of the filament is proportional to the 4th power of the temperature of the filament.  When you start seeing red instead of white, not only is there a smaller proportion of useful light, there is less than 16th of total output at full brightness.


RE: light dimmer save energy?

Hi walker1,

Not so much PWM, but phase angle control. PWM costs more to implement, but lets you keep a more-or-less sinusoidal output: a useful for a motor load. Tungsten lamps on the other hand don't care whether the supply is sinusoidal or not, or even whether it is AC or DC, so the cheaper and simpler phase angle control is used. there is enough thermal lag in the filament so the somewhat chopped waveform doesn't cause noticeable flicker. I'm teaching my granny to suck eggs, so I'll shut up!


If we learn from our mistakes,
I'm getting a great education!

RE: light dimmer save energy?

The fact is though, if you can wind down the dimmer and the supply current falls, you are still reducing the Kwh and the running cost per hour of illumination.

Even if optical efficiency falls off very rapidly, if you can tolerate the reduced lighting levels, your electricity bills will also fall.

Another aspect is lamp life, which increases greatly at reduced voltage. If you only use the dimmer and not the switch to turn on the lamp, thermal shock at turn on will be eliminated. That dreaded "plink" and a blown bulb will become a very rare event.

I have done this in my home. Most of the switches have been replaced with triac dimmers. I now have knobs instead of rocker switches. I cannot remember when I last changed a bulb, it must be at least five to eight years.

The electronic fluorescent bulb replacements are good too and I have many of those as well (non dimmed). While they are economical to run, they still blow up occasionally, and are not cheap to replace. I wonder at the overall cost benefit of these, but have no figures.

But all my incandescents have had dimmers fitted for a very long time.

RE: light dimmer save energy?

Warpspeed I think I am spending maybe... 4X more using compact fluorescent... Reason?  They fail me at home and the office at a dismal rate.  They never EVER last me even a year.  The last one I put in lasted fully one month! I would have saved a fortune using incandescent.  I do have one C.F. that has lasted two years.  It is a 40W? = 200W T
in my hallway. It's probably been on a total of 40 hrs in 2 years.

They all seem to fail due to the heat.  Even tho they aren't in enclosures.  Most are in ceiling fixtures with the shallow glass bowl on below them open on all four sides.

They all look discolored having gone from white to off white.

I think they are built incredibly cheaply.  So cheap, I think it's going to hurt their reputation.  After purchasing more than forty of them...I hate them now.

RE: light dimmer save energy?

AM/FM Radio interferance with dimmers, can someone address this.
Thank You

RE: light dimmer save energy?

Sure pennpoint.. It's reeeal annoying.  That do?

Oh why it happens!!

  Well that's because whenever you have voltages or more accurately currents making sudden shape changes many harmonics are created.   Harmonics are like another waveform that is related to the signal of interest by an integer factor... That means 2 times, or 3 times, or 18 times, etc.   If these harmonics are *enough* times higher, then they reach up to frequencies that are high enough to travel thru the air same as the radio signals being listened to or thru the house wiring into the radio thru its line cord.

  Now as ScottyUK correctly pointed out these dimmers work on phase control not PWM... This means that to control the amount of power to something, less than full power (not a nice quiet, complete, smooth sine wave) the dimmer switch when turned down does the following.

  It suspends the AC power from leaving the switch until some serious fraction of a line cycle, say.. 50% has gone by then triggers on the power element in the dimmer circuit.
  This power element is a triac.  The triac can only be shut off once the power cycle reaches a point where zero current is flowing.  But it can be turned on everywhere(within limits).
  So the dimmer control waits until maybe half the AC line cycle goes by and triggers on the triac. buuzap! The triac current leaps to full current suddenly then abruptly starts following the AC power cycle until the next zero crossing where the current drops to zero and the triac shuts off.
  The dimmer control waits the same amount of the next line cycle and triggers the triac again... 120 times a second.
  These abrupt trigger ONs make nasty looking sudden current transitions everytime.  These give birth to tons of harmonics that come pouring out of the dimmer into the air and into the wiring.  Irritating your radios, TV's, and some other things.
  This can be fixed but it takes more components, space, and $money$ so often the cheaper the dimmer the noisier it is.
  Was this what you were asking pennpoint?

RE: light dimmer save energy?

itsmoked, that pretty well sums up my experiences with the compact fluorescent replacement lamps too. As you say heat is probably the greatest killer, most of mine here are rather small, typically 15W = 40W. I mainly use them in small rooms where only one bulb is being replaced.

With multiple bulbs I prefer incandescents with a dimmer. For anything other than reading, reduced illumination works fine.

RE: light dimmer save energy?

That is exactly the kind of circuit I buit 30 years back, when I was still a trainee.

I thought we had somewhat moved away from those noisy buggers.

Or maybe we are just more strict here in Scandinavia?
After all, Walmart and extremely cheap and uncontrolled electrical goods from China are not as common here.
Fans, cords and plugs, yes. Dimmers, no.

And yes, it does work on the phase of the input voltage, but it still reduces the outout power by reducing the time the load 'sees' mains. (I.e. primitive PWM, hm ?)
But let us not make this into a fight over the emperor's beard, as we say

RE: light dimmer save energy?

For some reason, the 13 watt Compact Fluorescent bulbs are garbage. Their failure rate seems to be much higher than any other type of CF bulb. Certain brands ('Globe') have even been recalled as a fire hazard, but I believe that there are other brands (likely made on the same line in China) that share the same problems but haven't been recalled. There were even reports of fake CSA (UL) marks.

I've never had any problems with 15 watt, 23 watt and 45 watt CF bulbs. They seem to last for years...  If you've had trouble with CF bulbs, then don't give up on them totally.

Light dimmers are more-or-less obsolete due to being incompatible with CF bulbs. One might have a light dimmer for the dining room fixture, but that's about all.

The next wave will be White LED lighting. It is probably less than 10 years away...

RE: light dimmer save energy?

As the tangential arguments continue and the original poster has apparently been blown away over how much discussion this topic has generated, I can see that nobody has addressed the part of your question about what to do about the noise. The probelm is, it isn't simple. The best solution is to install a choke of some sort into the system, but that unfortunately should have been done by the dimmer mfgr as it is going to be nearly impossible to put one into the wall box with the dimmer now. This by the way is usually the difference between the $15 dimmer and the $30 dimmer, but they don't explain it well at the store.

If you have room, you may try adding a small toroidal choke or ferrite core as they tend to offer the best performace for their size. Something like this, if you can figure out how to adapt it.


"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."   
Nikola Tesla

RE: light dimmer save energy?

That white LED illumination is most likely closer than you think.

A local library here in Copenhagen uses LED lighting on stairways etc. Not prime illumination yet, mere guidance, but..

I did see something on the news the other day about actual lamps for home use.

White LED bicycle headlights are in common use here.

Quite a few trafic lights here in town are also now 100% LED. (Green, yellow and red, not white, I know

RE: light dimmer save energy?

It's not a question of LED brightness, but of efficiency... bulbs still have the edge when it comes to overall light output efficiency.  But it's getting quite close, and I would expect in the next 5-10 years to see commercially available LED units that are more efficient and less expensive (over the long haul) than bulbs.

I use some REALLY strong LEDs in my work (25W anyone? [:D] ), and they easily light up an area of a room, but when it comes to overall lighting of a room I run back to bulbs.


RE: light dimmer save energy?

I have an aquarium. I used to have five 180W MH on pendants hanging over it... 1000W 18 hours a day..

18 X 1KW * 30days * 0.26/KW-hr = $140.00/mo.

I don't have them anymore.. :(

I picked up an LED floodlight. Has 88? LEDs in it. Cost almost $300.  Very nice light for like 8 watts.  But still way too little.  From it I caculated I would need about 3,000 white LEDs to light one third of the aquarium correctly.. :( :(!

They really aren't quite ready for prime time. Some of the newest strange ones are getting there though. The multi-watt single LEDs.  Wonder what they cost.

Which brand do you use macgyvers2000?

RE: light dimmer save energy?

jraef and itsmoked

Thank you both for your tutorial on line noise.

I'll swap out the cheapo dimmer.


RE: light dimmer save energy?

Personally I hate the colour of the CF light. It gives me headaches.
If I was going to have LED lighting, I'd also be checking the colour carefully. The white LEDs have a very blue colour (and doesn't that sentence sound daft, but you know what I mean) which, to my mind just isn't relaxing.
I use mostly 40W incandescent bulbs as indirect lighting, which is fine for general use. The ceiling lights are 6 X 100W which are used when we really need to look carefully at something.
I believe you can now get 2-way dimmers, which is a bit darned clever, and when I get the huge pay rise which always seems just over the horizon, I might splash out and get some of those.

(As an aside: why did they stop making 3 gang intermediate switches? My mum's really upset that I can't replace the one that she's had for umpteen years)

"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

RE: light dimmer save energy?

There are phosphors that mimic the colour of daylight. Table lamps are available with these bulbs, but I'm not sure if the CF (screw-in) format offers these phosphors.

Headaches are often caused by flickering.

Some white LEDs are actually UV LEDs with white phosphors, so it is actually almost the same situation as CF bulbs.

RE: light dimmer save energy?

Actually, most white LEDs are blue chips with yellow phosphor, which explains the strange colour (red is missing).
For future applications, UV LEDs are indeed being looked into, but the technology is hardly mature at this point. With UV LEDs, it's poosible to make any colour depending on the phosphor mix (eg, pink).


RE: light dimmer save energy?

RobWard;  Not that I can even recommend the dang things with my experience, but there are CFs that have the reddish tinge of tungsten (they call it a warm color).  I have used several. (briefly)  Often I would get a warm colored one and pair it with a cool(bluish) one in a ceiling fixture.  That was very nice!  (while it lasted) :)

RE: light dimmer save energy?

Question somewhat related to the thread:

Does anyone know how those devices work that allow you to touch a metal part of the lamp to turn it on?


Where do you live, that you pay $0.26/kWh?  Yikes!


RE: light dimmer save energy?

Those touch switches work off of the added capacitance of your body to trigger a comparator

Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.

RE: light dimmer save energy?


Santa Cruz, CA

RE: light dimmer save energy?

Sorta Back to the second original question loosely regarding the operation of light dimmers (some light dimmers, anyway); when I was a kid my dad told me the white knob controlled a variable capacitor.  At the time I had no idea what the heck he was talking about, but now, I presume the variable cap was in series with the lamp and by adjusting the capacitance you adjust the impedance in series with the lamp thereby decreasing the voltage across the lamp, etc...

I vaguely remember when the knob was rotated for full light output there was a slight clicking action.  I assume the clicking action was a simple mechanical switch responsible for bypassing the variable capacitor.

RE: light dimmer save energy?

Your dad was a EE?


RE: light dimmer save energy?

My dad has been a self taught electronics technician since he was a teenager.  He was fixing transistor radios since he was 13.  In fact both of my grandfathers were electronics fix-its, but nowhere near at the same level as my dad.  A lot of people may not think much of him, but I have always looked up to him...and, frankly, as corny as it may sound, I always hope every cool electronics design/project I complete impresses him.

Anyway, that's just what my dad told me.  I don't know if it is true that at least some incandescent lamp dimmers are made almost entirely a single variable capacitor or not, but it sure seems reasonable.  And if it is true (back to the first original question loosely regarding lost power), there will be little real power loss - just a crummy power factor.

RE: light dimmer save energy?

Um...  Not to cast aspersions but I doubt any dimmers were ever capacitor droppers.  The cap would have to be dang large and variable caps for power are large and clunky.  Lots of light dimmers are variable resistors called rheostats.  And lots of them for really big lighting loads like stages, etc. were variable transformers called variacs.  But variable caps.. no!

It could be that in a dimmer switch, someone, at one time, used a variable cap to control the traic circuit inside the dimmer... but even that is cumbersome.

Perhaps the TV was up too high and you miss interpreted what your Dad was saying. :)

RE: light dimmer save energy?

There should be some cautions made when using a triac controlled device in conjunction with some solid state voltage controlled devices.  Specifically, I have seen a Basler voltage regulator for a small generator set full field when a VFD motor controller was switched on.  Also, the triac current controller of a TIG welder caused the same problem.  A Basler model APR 125-5 regulator will full field the generator when some triac controlled devices are used.  Once you consider the damage that could occur, these noisy triac devices can be very expensive to use.

RE: light dimmer save energy?

I also doubt that your Dad had it correct as an "industry standard", but if he was like my Dad and learned to make do with what you had available during WWII, he may have gutted an old radio with a variable cap tuner, and discovered that it could make a small light dim if connected right. Just a guess though.

He could also have been like my Dad and told you a whopper just to see if you would buy it, waiting for the day when you discovered his deception and had the guts to confront him with it!

For those still interested, here is a decent site explaining it all, including a brief history of dimmers.


"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."   
Nikola Tesla

RE: light dimmer save energy?

gesh jraef why'd you get all the stars?!?

I live for stars.....

RE: light dimmer save energy?

Well, I can't give myself stars if that's what you were implying! Someone obviously liked something I said. I live for purple stars too. My boss lets me trade them in for candy bars at the end of the month!

"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."   
Nikola Tesla

RE: light dimmer save energy?

Ah...  I got my star! Now I can sleep peacefully...

RE: light dimmer save energy?

"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."   
Nikola Tesla

RE: light dimmer save energy?

Here's an additional question. I have a torchiere lamp with a fluorescent bulb and a dimmer switch.  How does the dimmer switch work?  Is there a dimmer switch available for separate fluorescent lights?  Ok ok. That's two questions.

RE: light dimmer save energy?

jraef......Never let the truth get in the way of a good story!

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