# Dimming issue with LED



## Mshow1323 (Jun 9, 2012)

Is the dimmer listed for LEDs? Are these bulbs listed for dimming?


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## spark E (Jul 9, 2015)

Yes and yes


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## Dennis Alwon (May 9, 2009)

spark E said:


> Yes and yes


The problem is the dimmer may not be tested for that bulb. Lutron, for instance, will only guarantee the bulbs that they have tested to be used with their dimmers. Change bulbs and see what happens- use a Cree or Phillips type bulb


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## telsa (May 22, 2015)

LEDs are not only solid state -- they are ultra rapid in their response to their inputs -- being for all practical terms almost about as fast as a transistor... ( well, not quite )

Which is in direct contrast to an incandescent lamp -- which emits 'black body radiation.' (It's just an expression, the filament is white hot.) 

Current flow is used to 'roast' the filament. If the current is interrupted for a split second, the filament cools down -- but is still hot enough to emit light. A fresh pulse brings it right back up to full heat. With each chopping, the temperature -- and current used -- drops. But these on-off sequences are buffered by the physics of a hot filament.

Consequently, the dimmers that you've got pulsing your LEDs are perfectly fine with incandescent lamps. 

LEDs expose the 'current chopping' -- actually performed by transistor logic. They are clipping off the AC wave form. (typically -- other schemes are possible) This clipped current is rectified and sent to the LEDs. 

{ The voltage, per se, is not manipulated. The dimming result is created by turning the circuit full off and on -- super fast. }

In your particular case, the dimmer that you've installed has no provision to buffer the EMF through the 'off period.' Neither does the driven element -- the LED 'lamps.'

So, you're left with actually witnessing the on-off-on-off-on-off... cycle as a flicker -- which is running at 120 Hz, I'd bet. ( 60 Hz x 2 half-cycles )

The above, without getting too wordy, is where your flicker is coming from.

Your cure is to get wholly different dimmers specifically engineered for LEDs. These will have provisions to buffer the choppy energy wave (think capacitors) so that its 'off cycle' is not so long as to make it blink 'out.' 

&&&&

The same result can be had by LEDs with different phosphors. These have a different decay curve (of visible light emission) so that THEY can handle your choppy dimmers.

&&&&

So now you know WHY the above posters said what they said.

EITHER component -- once changed -- can cure the flickering problem. 

The deal is that the optimal solution REQUIRES that both dimmer and LED be mated -- back at the design lab -- as this is -- for all practical purposes -- a 'tuned circuit.' 

For both the power source and the receiving element have to be 'happy' with each other.

When "changing dimmers" is mentioned -- no-one means merely changing the particular units in your hands. They mean you have to swap to an entirely different -- and appropriate device.

As you may have guessed. It won't be the cheapest on the shelf... not by a long shot.:no::whistling2::blink::laughing:


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## telsa (May 22, 2015)

Since you're a fourth-year:

Topics worthy of study...

Black body radiation

Pulse Width Modulation

Edge triggered circuits

Diode bridges

Phosphors -- and their decay curves

Newton's law of cooling

And even...

Negative temperatures

ALL of the above are Google (worthy) terms that a fourth-year should be able to handle.

Cheers.


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## randolph333 (Feb 10, 2015)

The short answer is that some dimmer/driver combinations create flicker, others don't; you need to select them carefully, and perhaps even experiment, to avoid flicker.

Extended discussions from Lutron of some of the technical issues of LED dimming may be found here http://www.lutron.com/TechnicalDocumentLibrary/048360a_PWM_vs_CCR_LED_App_Note.pdf and here
http://www.lutron.com/TechnicalDocumentLibrary/3683586_Challenges_of_Dimming_Whitepaper.pdf .


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## spark E (Jul 9, 2015)

Thanks guys for help, I have swapped out numerous dimmers but never tried swapping the bulbs. Problem there is the potlights were purchased at costco and came as a set bulb and fixture. 

Lucky this job is for my brother and not a customer or I would be in some major crap. Live and learn I guess. Much appreciated for all the in depth repsonses!


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## duque00 (Sep 11, 2008)

Spark - get the make/model # from the box that these potlights came in.

Check the box or Goto the manufacturers website for dimmers that are rated to work with these specific potlights. Swap dimmers for the right ones and you should be in business.

Post up a pic of the fixture and the box. Also, let us know what the make/model it is.


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## randolph333 (Feb 10, 2015)

I'd be interested, too. And I've never heard the term "potlight" before. Is it generic for recessed can? Or is it more specialized? And what part of the English-speaking world uses it?


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## B-Nabs (Jun 4, 2014)

randolph333 said:


> I'd be interested, too. And I've never heard the term "potlight" before. Is it generic for recessed can? Or is it more specialized? And what part of the English-speaking world uses it?



I live three hours' drive north of you, and pot light is the single most common vernacular term for recessed down lights around here.


Sent from my iPhone using Tapatalk


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## Electric_Light (Apr 6, 2010)

telsa said:


> LEDs are not only solid state...


But the ones that emit white light are fluorescent lamps and they require a ballast, which is usually built into the lamps. 



telsa said:


> The deal is that the optimal solution REQUIRES that both dimmer and LED be mated -- back at the design lab -- as this is -- for all practical purposes -- a 'tuned circuit.'


LED products are still immature developing novelty products and they have many issues just like earlier CFLs. More troublesome are the relabeled, Made and designed in China products only concerned with shelf price and getting out to the market as soon as possible. 

Lamp - ballast - dimmer compatibility. Try and see, and repeat it until you find satisfactory results. 

Buzzing. 
Premature failure. 
Failure to meet specs. 
Failure of purveyor prior to product warranty expiration. 
Immature testing standards. 
Performance degradation such as color fading. 

Those are some common concerns with "LED" type products. I certainly understand your frustration. I have experienced the same dimmers recommended for LED use, and LEDs claiming dimmable have the same type of issues you're having and this is just something that comes with what I still consider experimental products in the wild west.


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## B-Nabs (Jun 4, 2014)

Electric_Light said:


> But the ones that emit white light are fluorescent lamps and they require a ballast, which is usually built into the lamps.
> 
> 
> 
> ...


You forgot to say "shoulda used T8s"


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## spark E (Jul 9, 2015)

Thanks duque, I am heading to my brothers this weekend and will snap some pics of the box, I believe the GU10'S are a Bazz brand.

As for the term potlights, it is heavily used here in Winnipeg, Canada. Lol


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## spark E (Jul 9, 2015)

B-Nabs said:


> Electric_Light said:
> 
> 
> > But the ones that emit white light are fluorescent lamps and they require a ballast, which is usually built into the lamps.
> ...


"Should of used a standard switch" more like it


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## Going_Commando (Oct 1, 2011)

Electric_Light said:


> But the ones that emit white light are fluorescent lamps and they require a ballast, which is usually built into the lamps.
> 
> 
> 
> ...


Great answer to the OP's question! You honestly think fluorescents are a better alternative to LEDs for dimmable recessed cans in a house? You are just a looney.


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## Electric_Light (Apr 6, 2010)

In-line dimming over the power wires using phase-cut is challenging as there are no specific standards. Just like Lutron says, dimming LEDs require hand fitting to make sure proper dimmer/LED ballast compatibility. 

LED ballast does not look like an incandescent lamp to the dimmer and not all electronic LED ballasts react the same to the same dimmer. LED bulbs are disposable items just like CFLs and with the LED element costing a lot, it doesn't leave more than a buck or two for the ballast.


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## Fred_W (Jul 3, 2015)

It's pretty tricky with the Gu10 9w bulbs, in most cases the power supply is internal, and the bulb has small space for the power supply, however a dimmable power supply is comperatively larger.... 

We'll release some Ra > 90. R9 > 50 high quality downlights and spotlights, there are for commercial applications. And they all have external power supplies.


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