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Halogen bulbs flickering with dimmer.

rickie's picture

Thanks in advance for any input you may have. My problem is flickering of recessed lights when using a dimmer switch. I have six (6) 60 watt halogen bulbs in recessed fixtures wired as a three way with a lutron dimmer on one switch. This particular dimmer switch is in a three-gang box with two other dimmers which are also part of three way switches. A 20 amp breaker services these. I get significant, but sporadic, flickering under specific circumstances: when the dimmer controlling the six halogen bulbs is dimmed below halfway and the other two switches are off I will get flickering. When I turn on one of the other switches the flickering stops. When the dimmer is set to high (not dimming much) the flickering goes away. I have already replaced the dimmer switch with a new one (still flickers) and also replaced it with a regular switch to see if there was flickering then, there was none. This is brand new wiring in a new addition and I checked the integrity of the connections at the panel and switches and all seems fine. Is it simply the halogen bulbs? I feel stupid for not replacing them as a first step but figured since they have a filiment and are similar to an incandesent bulb in that way it was likely something else. But now its either the bulbs or something I don't yet understand.

Thanks folks.

(post #70195, reply #1 of 28)

The choppy waveforms from cheap dimmers can cause the filiments to vibrate causing the flicker. You can hear them vibrating if you have good hearing, it's a kind of high pitched noise. 

(post #70195, reply #2 of 28)

I'm using Lutron DV-603P dimmers. They seem of reasonably good quality, or at least are priced as such.

(post #70195, reply #3 of 28)

Experiment with some different bulbs.

(post #70195, reply #10 of 28)

   Hello Mark,

I think they call that "60 Cycle Hum".

(post #70195, reply #12 of 28)

I believe the vibration it is a harmonic of the 60 hz chopped waveform, but the resonant frequency of the filament seems much higher, because the sound is rather high pitched.

(post #70195, reply #27 of 28)

" A harmonic of a 60 cycle chopped wave form". Well, Mark I had to Google the dimmer switch before I jump with both feet into very deep water! Live and learn! So its the shifting magnetic field, forming the chopped wave form and that is causing the noise! They call it a "Triode Alternating Current Switch". So from what I now understand, its a cheap dimmer switch (LOL), which also can generate weak radio signals that can cause interferance with near by radio and TV reception. Head for the High End Dimmers, with a choke circuit built in.

I also learned that halogen bulbs must operate at full voltage to maintain the filament life listed on the bulb package. Vary interesting, Mark, you opened this old farts eyes. I will make an offering to the Computer Gods, Monday afternoon!  LOL.....Pop


(post #70195, reply #28 of 28)

They aren't just rheostats anymore.

(post #70195, reply #4 of 28)

OK, flickering.  How fast is it?  Light sources like flourescents turn on and off fast enough to follow the 60 Hz. AC cycle, producing 120 light pulses per second.  Incandescents, of which halogens are a special kind, take longer for the filament to heat up and cool down.  Light output doesn't drop to zero between half cycles, but there can be a substanital ripple at 120 Hz.  The delayed triggering of triac dimmers would exacerbate that ripple, but it would take a very low mass filament and something like spinning fan blades to detect it.   Optical sound heads on movie projectors used very well filtered DC with incandescents, because the ripple would get isolated and amplified.

If the flicker is significantly slower, it could be a triac triggering problem.  If the delay gets longer than a half cycle, it'll only trigger in the next half cycle, reducing the flicker frequency to 60 Hz. 

If it's even slower and random, then we should suspect a contact problem. 




-- J.S.




-- J.S.


(post #70195, reply #6 of 28)

How fast is it? I'd say the flickering is pretty slow in cycle. And when the flickering occurs it seems pretty random. Under the circumstances I described in my original post (dimmer set below halfway with the other fixtures sharing the circuit off) there can be a long time between noticeable flickering, several minutes or more, but when they flicker the lights can drop off almost completely for about a quarter of a second or so (or so it seems), very, very noticeable, or they flicker a little less severely but still in the .1 to .2 second range. I may be wrong, but I thought it would be an important piece of diagnostic information that when there is flickering, always with the other fixtures sharing the circuit off, as soon as one of the other fixtures (separately switched) sharing the circuit is turned on the flickering immediately stops. Also, there is no flickering when the dimmer is set to high (little to no dimming). Do you think regular incandescent bulbs would help the problem or at least the diagnosis? The halogens work well for this application but I'm not wedded to them. Thanks for taking the time to respond.


Edited 1/30/2006 7:34 pm ET by Rickie

Edited 1/30/2006 7:35 pm ET by Rickie

(post #70195, reply #7 of 28)

My observation of flickering in the .1 to .2 of a second range is my perception, I could be far off and I have not thought about the timing in very technical terms. As you can see, I am not an electrical engineer.

(post #70195, reply #11 of 28)

Halogen bulbs are dimmable. It does not drastically cut their life. However, you don't get the full features of "life cycle". To do that you need to run them at full power from time to time.

Now back to your problem. That is a strange one based on the way that the dimmers work. Most problems of this sort are more of a regular flicker and not the slow cycle that you are seeing.

Are these line operated lights or low voltage with a "transformer" (which might even be in the fixture). And if low voltage is is a magnetic transformer or switching power supply (aka an "electronic transformer"). Thos often don't work with standard dimmers and will cause problems like you describe. Special dimmers are needed.

If these are line operated bulbs you said that you replaced the dimmer, but was it with the same brand/model? If so you might try a completely different type.

IIRC in your first post you said that the problem was also affected by a nearby dimmer or some other equipment?

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #70195, reply #13 of 28)

LV dimming and the wrong type dimmer....I was thinking the same thing ....,

many years ago when dimmers first showed up and were ganged like these , there was a capacitive reactance between them and the lights were visibly affected....they would vary in brightness at "full", and the filaments were noisy and vibrating.
I recall a condo complex where there was five or six dimmers in one hallway in the "A" units and the last lamp at full range was less bright of any other two lamps

the solution as I recall , was to put only two dimmers in a box.

and all on one circuit I think

. . .

. . . . . . . .

(post #70195, reply #16 of 28)

I don't believe it has anything to do with the halogens.  I have had the same experience with regular incandescents.  Even the highpriced dimmers do it in certain ranges. 

I suggest you run a test --- either by feeding your present line to an ordinary incandescent (even a trouble light), or by swapping a dimmer of the same type for one of your conventional toggles.  To run the test, set the dimmer in the range where you describe the problem is occurring.  Then wait awhile.  It sometimes takes 30 minutes or so for the flickering to start.

Curiously, this phenomonon does not happen with the old-fashioned (cheaper) knob style dimmers.  (You could run that test also, for about six bucks.)



(post #70195, reply #17 of 28)

Update. Firstly, thank you all for your input. I went ahead and swapped out all six halogen bulbs with plain old incandescent bulbs, 65W. I still have flickering. I am truly surprised, but then again I'm not that bright. Just to reiterate, I did replace the dimmer (yes, same model dimmer) and still flickering. I temporarily installed a non dimmer toggle switch and had no flickering, but then again I get no flickering when the dimmer is set to high (little dimming). Without dimming the output is blinding, a dimmer is definitely required for this application. What still puzzles me is in the midst of a flickering spasm as soon as I turn on one of the other switches sharing the circuit the flickering stops. I'm scratching myself a bald spot (bigger one) over this, and have just about exhausted my diagnostic options. The electrician says he'll come back and check the connections, but I've basically already done that save for at the recessed fixtures themselves. I would appreciate any further input, and if when writing you treat me like an eight year old that may help. Also, this is not a low voltage set up, normal line voltage.



Edited 2/1/2006 9:47 pm ET by Rickie

(post #70195, reply #20 of 28)

it could be a triac triggering problem

I'm wondering if it's an inductance thing, with the other switches in the gang box (remember the problem goes away with an additional switch thrown).  I've never installed more than one of the $30 Lutrons in one box before (more for coverplate issues), so I don't know if they will "bleed over" into each other.  I know the old "twisters" would have odd harmonics ganged together, sometimes.

Occupational hazard of my occupation not being around (sorry Bubba)
I may not be able to help you Occupational hazard of my occupation not being around (sorry Bubba)

(post #70195, reply #5 of 28)

Some halogens cans will flicker if they are overheating as well. If they are not the ones in the boxes, check to see if there is sufficient clearance between the insulation and the fixtures.

(post #70195, reply #14 of 28)

Thermal cutout would be a good bet except that turning other things on makes the flicker go away.  Some can fixtures have thermal protection built in, and will cut out with either tungsten/halogen/quartz or conventional tungsten/argon/borosilicate lamps if the wattage and heat are too high.



-- J.S.




-- J.S.


(post #70195, reply #8 of 28)

Halogen lighting is not meant to be dimmed. You will end up with very short lamp life, the halogen cycle redeposits the tungsten on the filament at operating temperature. At reduced temperature the halogen cycle redeposition does not take place.

Have plenty of spare lamps.

(post #70195, reply #21 of 28)

Halogen lighting is not meant to be dimmed

Huh?  Sure are a lot of dimmer products for both LV & Line voltage halogen lamps if they are not meant to be dimmed.

Sure you are not thinking of HID lamps?  Can't dim them for love nor money (even if they are highly unlikely kitchen lighting fixtures <g>).

Occupational hazard of my occupation not being around (sorry Bubba)
I may not be able to help you Occupational hazard of my occupation not being around (sorry Bubba)

(post #70195, reply #24 of 28)

Halogen bulbs are filled with halogen (Iodine or Bromine) to scavenge the tungsten metal off the quartz bulb. When the bulbs are hot enough the halogen gas returns the evaporated metal back to the filament, ie the halogen cycle. Too cool and the metal does not make it back.

Too hot and you melt the leads to the bulb. If you touch the quartz bulb with your fingers the oils from your skin form an acid that etches the quartz eventually causing it to fail.

So if you are dimming your bulbs and they are dark inside and failing quickly, I would either substitute a regular bulb or forego the dimming or put up with short lamp life.

Am I sure,,,,well it was the lecture topic one day in optics at Rochester Institute of Technology. I paid cash money for the education, just passing it along for free after 35 years.

(post #70195, reply #25 of 28)

You can run them at 100% for a few minutes just before turning them off to clear the tungsten off the inside of the envelope, and not lose as much lamp life.  The issue with fingerprints or other contaminants on the outside of the quartz is that they can absorb enough heat to cause it to melt thru.  If the filament breaks causing an arc, pressure and heat build up and eventually pop the envelope.  People used to be scared of that in the early days, especially with open face instruments.  I saw it happen once on a 2k, it's not that big a deal. 



-- J.S.




-- J.S.


(post #70195, reply #9 of 28)

Does the light package say that the bulbs in question are dimmable?  Like others have said about halogen some bulbs are not made to be operated that way.  One immediately comes to mind those energy saving halogens are not dimmable you have look real hard on the package to find it but its there.  When in operation some will flicker some will flash and then go out until you turn the dimmer back up to full strength.  Not a high paid  electrician either just really good nail bender, just sharing what little I know about this subject good luck.

Matt- Woods favorite carpenter. 

(post #70195, reply #15 of 28)

Bill H is right that halogen lamps themselves are always dimmable.  What may be a problem is if they are low voltage, the transformer, or whatever else is in that black box, may not play nice with certain dimmers. 

Dimming does reduce the life if the quartz envelope isn't kept hot enough.  Running them up to full power for a few minutes before turning them off solves that problem.  In the early days of halogen studio lights, some gaffers would do that if time permitted.  But in those days a 10k halogen lamp was over a thousand dollars, and a thousand was a lot of money in the '60's - '70's.



-- J.S.




-- J.S.


(post #70195, reply #18 of 28)

I would call Lutron tech support and ask them. They are there 24 hours a day and have always been very helpful when I had a question or problem.

One other thing to consider, is that if you have three lutron diva dimmers in one box, you have to derate the ones you remove the side heat sink/fins from. For a diva, if you remove both the left and right fin from the dimmer to fit three in one box, the max capacity of that dimmer drops from 600 watts down to 400. I am not saying this is your problem but it is something to be aware of.



(post #70195, reply #19 of 28)

Nor is it due to heat - derating.  These dimmers perform pretty much the same unacceptable way when loaded with several ceiling cans (as in your case) even if there is only one dimmer in the box and the cover plate is off --- i.e. cool as they can get.

For $5.99 from HD, try popping a push-on/push-off knob-style dimmer in place of your Lutron and see how that performs (perfectly is my experience).  Then you will really have something to tell the Lutron support folks.


(post #70195, reply #22 of 28)

Aha -- If it's one of those goofy Lutrons with the LED's down the side, I'd just toss it and go with a simple rotary Leviton.  In fact, I did just that with the last house we bought.  Nobody could figure out the Lutrons. 



-- J.S.




-- J.S.


(post #70195, reply #23 of 28)


Nobody could figure out the Lutrons. 

I have about 25 Lutron Maestros and a Grafik Eye system in our house and we love them. My only regret is not spending the extra cash when we built to upgrade to a Radio Ra or at least Spacer system to get more connectivity between the dimmers. 



(post #70195, reply #26 of 28)

Thanks all, but I think DJJ gets the prize for this one. My 65 watt bulbs (six of them) might have been drawing too much with the spacer fins cut off. I replaced all six bulbs with 45 watt incandescent floods and so far no flickering.