# LED Lamps with voltage dimming



## Esoteric (Apr 14, 2010)

Hey guys, so I am working on a house light conversion for a worship center to LED. I have the design done and spec'd out, but then an electrical company comes through and shows the client an LED lamp that they say can be dimmed using line voltage (an SCR dimmer). I explained to the client why this can not be done, but he wants to see papers/studies on the effects to the lamp if you do try to dim it using line voltage. Can anyone point me to some good, scholarly papers/studies on the effects of voltage dimming LEDs on the life of the diodes?

Mike


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## sk8rsdad (Apr 14, 2010)

Well...

It actually is possible to dim LEDs by varying the voltage, but the effect is nonlinear and the LED won't light at all until it reaches its threshold voltage. The simple way to get more linear behaviour by introducing resistors in parallel with the LED but now you're wasting power and generating more heat in the circuit. The smarter way to dim LEDs is using some sort of PWM circuit. There may be vendors out there who have implemented some sort of variable voltage PWM circuitry too, but that seems an expensive way to go about it. So, it can be done, but if I were doing a new install it isn't how I would recommend doing it given the efficiency losses in both the LED circuit and the SCR dimming. The lamps might generate electro-acoustic noise too so it would be worth a demonstration before betting the farm on that approach.

This article explains some of the ways LEDs can be dimmed.

LED Dimmer


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## Esoteric (Apr 14, 2010)

Yeah, I know all that stuff, but appearently a Cree rep showed up and showed the client an $80 LED lamp that he could just screw into his current socket (driven by an SCR dimmer) to light his worship center. He claims that he could use his current SCR dimmers to dim the new lamps.

I have never seen or heard of anything like that. I have seen LED lamps that you can plug into a socket and dim, but they only dim to 20% before turning off. I have of course seen fixtures that dim either via DMX512 control or 0-10V analog control. But never anything you can screw into a socket and dim with normal voltage dimming. Especially not at 3000 lumens.

I am recommending a dedicated LED fixture, but I can't compete with an $80 lamp that the client can plug into his existing system.

Also, even if he isn't supposed to do it, he is thinking about doing it if the loss of diode life is in the 5-15% range. So he is looking for papers or studies done about how much life it will take off of a LED lamp to be dimmed (even if it is not supposed to be, as long as it will dim from 100-0 on a smooth curve).

Mike


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## JD (Apr 14, 2010)

Any model number? 

I would suspect it would not be a lifespan issue, but a dimmer curve issue. If it is made to run off a dimmer, then it probably does not contain a power supply and works with a long series of LEDs wired in series and a simple diode/cap/resistor between the lamps and the AC in. I would wonder how hot it runs (resistor basalt), how efficient it is, is there visible flicker, and, most important, what it looks like at lower settings. 

One other problem with long chain LED lamps (like traffic signals) is when one LED does fail, a large portion of the LEDs go out as well. (Like Christmas lights.)


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## epimetheus (Apr 15, 2010)

I agree with JD here. If the supposedly dimmable LED lamp is designed to run on dimmed (chopped) line voltage, then there is most likely not a LED driver circuit inside the bulb. This means that the end effect is going to be largely dependent on the dimmers in use as well. If the client is using IMAG or video recording of services, LED's on chopped line voltage will most likely cause flicker issues. They will also most likely not behave nicely at the low end of the dimming curve. Also, regular theatrical dimmers may not be happy with the much smaller load presented by LED replacements versus the incandescents.

I'd call the person suggesting this LED replacement lamp to the carpet and get a demo. If the client is using video, make sure they have a camera setup in their typical service configuration for this demo. That's what we had to do at my church when we did our lighting upgrade last year. We had to 86 some Irradiant LED's because their flicker was horrendous on camera.


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## Esoteric (Apr 15, 2010)

Thanks guys. I called Cree and they claim they do not have a unit like that in their inventory.

I will let you know what else I find.

Mike


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## millamber (Apr 15, 2010)

A quick google search provided this...

HIGH POWER LED SPOTLIGHT ,LED DIMMING SPOT LIGHT,LED DIMMABLE SPOT LIGHT - GosoLED Lighting Co.,Ltd

I have no idea how it looks or anything measureable, just providing some info.


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## Malabaristo (Apr 15, 2010)

Cree does make LED lamps that are directly dimmable:Cree LED Lighting : LED Lighting Fixture Products Options Accessories I know this because I've tested a few different models. Their light output is really good (though definitely not 3000 lumens), and the dimming performance is extremely smooth. The really big disadvantage (at least in a theatrical setting) is their limited range of dimming. As noted it's something like 20% to full. That might be useful in some architectural settings, but it's pretty useless for theatrical house lighting. Note that as with fluorescent ballasts that's 20% of measured light output, so it actually looks much brighter than you might expect.

You won't find any papers on the negative effects of dimming an LED because there aren't any. The only real concern about LED fixtures is whether or not the driver is intended to be dimmed. Dimming one that isn't meant to be is potentially a very good way to shorten its life. If it's a product that's meant to be used with dimmers, then doing so will not have any negative effect (unless it's a really poorly designed product). These products will typically have active electronics driving the LEDs as that's the only way to get anything resembling decent performance. Even then, the best performance will be comparable to a good fluorescent ballast. The only products I've seen that approach incandescent dimming performance are ones where you have separate power and control signals.


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## Esoteric (Apr 15, 2010)

Yeah Malabaristo, I saw that they have lamps that dim 20%-full, but those would be completely useless in this application. They also do not have nearly enough output to get the job done well. Which is bad form by the Cree rep that talked to my client, as I guess technically he did not lie when he said they had a solution that would screw into his current setup and would dim, but that is VERY misleading and really not what I would expect from this company (although I guess with times being tough, anything is possible).

Mike


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## Esoteric (Apr 15, 2010)

millamber said:


> A quick google search provided this...
> 
> HIGH POWER LED SPOTLIGHT ,LED DIMMING SPOT LIGHT,LED DIMMABLE SPOT LIGHT - GosoLED Lighting Co.,Ltd
> 
> I have no idea how it looks or anything measureable, just providing some info.



Yeah, that doesn't give anywhere near enough information to compare that unit with any other.

Mike


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## epimetheus (Apr 15, 2010)

I'm going to go out a limb here and say that I don't think a direct screw-in replacement exists that will work as a theatrical/worship center house light. They just don't have the output or the dimming capabilities yet. That's not say there havn't been major strides lately, but the products just aren't there yet as far as I can see.


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## Esoteric (Apr 15, 2010)

That is what I thought.

Mike


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## DELO72 (Apr 15, 2010)

Actually, this may change soon. Sylvania for example is releasing an entire family of LED retrofit (E27 screwbase) lamps in Q3 of this year that are designed to be fully dimmable. Output on the non-dimmable PAR38 ones currently on the market by a few companies right now is comparable to the incandescent bulbs in both Color Temp, beam, and intensity. Price is obviously way higher (~$70 vs. ~$5). I think at this time we are talking <150W TH equivalent for matching output, but that is a guess. 

Aside from Cree, you might want to give GE, Philips, and Sylvania a call and ask to speak to the Product Marketing Manager in charge of LED Retrofit Lamps. That's the person who will be able to tell you what they have available currently, and what it is capable of replacing.


Cheers,


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## Esoteric (Apr 15, 2010)

Yeah, no one has a product out there (or in development that I know of) that would be fully dimmable with a normal curve and match the output of a 350W PAR light, much less get the 20% increase that they would like over that in output. I have talked to GE and Phillips and neither have them. That is why I am spec'ing an entire unit as opposed to a replacement lamp.

But I will keep my eye out for that lamp from Sylvania in Q3.

Mike


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## SteveB (Apr 15, 2010)

DELO72 said:


> Actually, this may change soon. Sylvania for example is releasing an entire family of LED retrofit (E27 screwbase) lamps in Q3 of this year that are designed to be fully dimmable. Output on the non-dimmable PAR38 ones currently on the market by a few companies right now is comparable to the incandescent bulbs in both Color Temp, beam, and intensity. Price is obviously way higher (~$70 vs. ~$5). I think at this time we are talking <150W TH equivalent for matching output, but that is a guess.
> 
> Aside from Cree, you might want to give GE, Philips, and Sylvania a call and ask to speak to the Product Marketing Manager in charge of LED Retrofit Lamps. That's the person who will be able to tell you what they have available currently, and what it is capable of replacing.
> 
> ...



Mark

First a hearty welcome to CB, as I don't recall you posting here prior and let me be the first (or not) in welcoming you. Industry representatives such as yourselves have so much useful advise and information to give, so a thanks in advance for joining.

And as a second, it's good to know that all the lamp manufacturers such as Osram, etc are investing as much as they are in LED's, though obviously you can't afford to not, but we in the theater end have always been the poor cousins in terms of trickle down technologies, so every bit helps.

That said, I (and many others I'm certain) read with a touch of skepticism when the term "Fully Dimmable" is used, for as you may well discover, most of us in the theatrical lighting business have a somewhat narrow definition of that phrase. To us, it needs to be consistent to 5% or so and by consistent I mean each and every lamp needs to respond to the same output from full down to 5%. Anything less doesn't meet the definition. 

As example, I have a ETC Unison architectural control system, that runs (when needed) the movie presets. Our projectionist was disappointed that he could not get a desired level on incandescent house lights of 4.5%, as 4 was too dim and 5 too bright. 

That's what we deal with on a daily basis and I'm not yet seeing that with DMX controlled LED fixtures designed for theatrical use, much less believing that it's a soon to be product running on dimmers and line voltage. It'll be great when it happens though....

In the mean time a thanks for the advise and references


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## Esoteric (Apr 15, 2010)

I dunno Steve, many of the latest generation of theater LED fixtures will dim evenly from 0-100% and even in increments as small as 1 DMX pt.

I assume you are using the Unison seperate from a DMX controller? Or else you could set the 4.5% level on the DMX controller and then record it into the Unison preset box?

Mike


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## DELO72 (Apr 16, 2010)

Thanks, glad to pop in. I've been haunting these forums for a while now as reader, mostly to keep up with what people are thinking and see what the feedback is on this or that lamp or fixture. 

The biggest problem I see with LEDs, which I hope will be fixed at some point in the near future (PLEASE Illumination Engineering Society-- Please?!?) is that there is no standard. So every company is creating their own versions of "white". What we need are ANSI standards for LEDs, or some agreement where the market says, here are the four versions that the market wants (for example: 3200K, 4000K, 5600K, 7000K-- instead of 20+ versions), and that is what everyone's versions will be. Right now one company's blue is different from every other company's, so you have to buy all fixtures from the same company if you want to color match easily--AND, unless they have really tight binning control on color from one batch/year to the next, even the colors within the same company's fixtures could be different. 

LEDs are like microprocessors in terms of how quickly the technology is growing and how much brighter and efficient they are getting every few months, but until there is some standarization, the market is going to suffer and it's going to be hard to get people to change from what they know works.

At least with Retrofits they are being designed to replace a current product already out there, so they should be very close/similar in color/output to what they are trying to mimic-- otherwise people won't switch. The confusion is when instead of making a "clone" product they only release what they think is an upgrade with a benefit over the current halogen product. Then you have to decide which company's version is better for you as they will all be different. Very annoying for the LDs! I feel your pain on that one.


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## SteveB (Apr 16, 2010)

Esoteric said:


> I dunno Steve, many of the latest generation of theater LED fixtures will dim evenly from 0-100% and even in increments as small as 1 DMX pt.
> 
> I assume you are using the Unison seperate from a DMX controller? Or else you could set the 4.5% level on the DMX controller and then record it into the Unison preset box?
> 
> Mike



I "almost" spec'd a compete set of Seledors as cyc lighting on a NYC Arts Council funding request. These would have replaced a set of L&E MR16 mini-strips. Issues I had:

1) It's tough to find a set of 3 or 6 @ 6ft all with lenses to try as demo. You really, really have to put them side-by-side to see what you're getting and how to make it work. 

2) I had a show recently that had a cyc color set or R61 pale blue, R64 blue and R68 med. blue. One thing that made me pause was how to cue their cyc into a set of LED's. The event was a morning kids show that gave me an Expression disk and I was going to have to go Q to Q to match what the LD wanted for each cue. Hmmm.... Now that's not a fixture issue as much a design issue, but one would question the usefulness of $75,000 worth of strip lights in this scenario, 'cause it's NOT a time saver !.

3) Mike D's comments about the speed in which the market is changing and the down-the-road compatibility with older gear, makes me pause. I can easily see a scenario 10 years from now of "Oh, you have the 3rd generation !, we're at 6th generation and while the replacement parts fit, the color is a bit different !" kind of response from the manufacturer (and that's a headache every manufacturer is going to be facing).

So while I'm certain the dimming problem, especially at low end has gotten better, there's still a lot of other things to consider before plunking down that kind of money

As to the 4.5% dimming levels ?, I used to have a Snapshot capability on my Unison system but removed it to gain processing head room on what became a bloated config. file, and in any event the issue of dimming to that kind of refinement is the issue and I'm not certain line voltage LED's as house lights would offer the level of control that an Ion can deliver and Unison can snapshot. Yet


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## derekleffew (Apr 17, 2010)

DELO72 said:


> ... LEDs are like microprocessors in terms of how quickly the technology is growing and how much brighter and efficient they are getting every few months, ...




SteveB said:


> ... 3) Mike D's comments about the speed in which the market is changing and the down-the-road compatibility with older gear, makes me pause. I can easily see a scenario 10 years from now of "Oh, you have the 3rd generation !, we're at 6th generation and while the replacement parts fit, the color is a bit different !" kind of response from the manufacturer (and that's a headache every manufacturer is going to be facing). ...



See Haitz's Law.


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## Esoteric (Apr 17, 2010)

SteveB said:


> I "almost" spec'd a compete set of Seledors as cyc lighting on a NYC Arts Council funding request. These would have replaced a set of L&E MR16 mini-strips. Issues I had:
> 
> 1) It's tough to find a set of 3 or 6 @ 6ft all with lenses to try as demo. You really, really have to put them side-by-side to see what you're getting and how to make it work.
> 
> ...



Oh, I am 100% sure that line voltage LED's can't, but there are all in one LED units out there that can.

I hear the color matching thing all the time. I guess it is not a big deal for me, because my professors always taught us never to look at the screen but to look at the stage because a 100/100/0 CMY mix on one unit will not always match a 100/100/0 CMY mix on any other unit, so you have to look up and make sure colors match even if one unit has to be 80/90/0 to match the other units 100/100/0. So I set every LED/CMY mixing unit separately anyway.

Mike


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## JChenault (Apr 17, 2010)

A short thread hijack.

A couple of you have mentioned the issues of color matching in LED units. In terms of market research - how much would it be worth it to you to have a solution that came much closer to matching colors between units.

The real question here is how much time do you spend matching colors? If you had a hardware device that could work with your console to calibrate your fixtures so color was consistent - how much time would you save? ( Assuming for sake of argument the system would be correct 99% of the time).

(Note - this discussion would of course apply to CMY units as well).

I've heard a lot of folks chat about how nice it would be to have a way to match colors - but I have not heard any real numbers about how useful it would would really be. Interested in hearing opinions.


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## Esoteric (Apr 18, 2010)

Honestly, it would be way down my list of things to get for one reason. I do two types of shows. Rock and roll where exact matching between units doesn't matter, and theater where I want matched colors, but I have enough time to sit and match the colors. So there are a hundred other things that I would find more useful.

Mike

YMMV


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