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Author Topic: Auditorium Dimmer with LEDs
Justin Hamaker
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From: Lakeport, CA USA
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 - posted 03-05-2017 10:16 PM      Profile for Justin Hamaker   Author's Homepage   Email Justin Hamaker   Send New Private Message       Edit/Delete Post 
We are interested in converting our auditorium dimmers from halogen at one theatre, and incandescent at the other. Both theatres currently have a Xetron XD-3KS panel - single channel at one theatre, dual channel at the other.

With this dimmer, would we be able to simply convert the bulbs to LED? Or is there some kind of change needed to handle the change in power requirements. My theatre uses the halogen bulbs, with 8 100w bulbs per channel. The bulbs have an E11 (miniature candelabra) base. I have tried a couple different LED alternatives and they don't work. Either they won't dim at all, or they are bright or off with no in between.

There is not problem with converting the fixtures to a different base - A19, or something else.

If this dimmer won't work with LEDs, are they any suggestions for one which will work with our automation system. We have the Christie ACT.

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Lyle Romer
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 - posted 03-05-2017 10:55 PM      Profile for Lyle Romer   Email Lyle Romer   Send New Private Message       Edit/Delete Post 
Have you used LED bulbs that are specifically marked "dimmable?"

I don't know the specifics of the dimmer you are using but I do know that not all LED bulbs are dimmable.

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Leo Enticknap
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 - posted 03-05-2017 11:52 PM      Profile for Leo Enticknap   Author's Homepage   Email Leo Enticknap   Send New Private Message       Edit/Delete Post 
We have Kelmar dimmers in two of our three houses, and in one of them I've put 20w (80w equivalent) LED PAR 38s, marked as dimmable on the packets. Works without any problems, except that they will only dim to a certain point (which is still quite bright) and then go out. The dimming isn't as smooth and as elegant as with old school bulbs, but it is saving us a lot of power, and staff time replacing blown bulbs. I installed those bulbs in January 2015: since then, one went flickery and had to be replaced, but that's it. Previously, we were having to do the ladder and grappling stick ritual about once a month.

However, I've noticed this with dimmable LED bulbs at home, too. When you switch them on, they don't light up at all until the slider is about half way up, and the same thing happens in reverse on the way down. They are sorta dimmable, but not as smoothly as a filament bulb is, and with a smaller range of brighness.

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Frank Cox
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 - posted 03-06-2017 12:59 AM      Profile for Frank Cox   Author's Homepage   Email Frank Cox   Send New Private Message       Edit/Delete Post 
I don't know why you would have to change the bulbs so frequently. I have a Kelmar dimmer and the bulbs that I use (standard 75w floodlights) last roughly forever. I think it's because the lights always come up and go down so slowly; the only time they get "shocked" and full-on immediately is after a power failure. I have six lights in my auditorium and I think I"ve changed them all once, maybe, in over twenty years of daily use.

I did try a "dimmable CFL" once to see how it worked, and it was a hopeless case. After dimming to a certain point that wasn't very dim, it started flashing on and off. So I bought about 20 of the 75w floodlight bulbs when they were on sale once upon a time, and figure that they will last me for as long as I need them here.

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Steve Guttag
We forgot the crackers Gromit!!!

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I'm amazed that the lighting and dimming industry hasn't gotten together on all of this. I guess that the market for people that need lamps to dim to zero is so small as to not warrant the change, yet.

LEDs don't dim like incandescents. It is kind of like a linear versus logarithmic taper faders. With a standard dimmer, you'll spend 70% of its range to dim the lamp about 10% and then compress the rest of the dimming in that last 30% so you need to change your upper limit and throw away that top 10% of its light. The other thing about "dimmable" lamps is that typically they are only rated to dim until 10% output and then it is all bets off from there. And even if you find a lamp that has the characteristics you like, there is no guarantee that it will remain that way on future purchases.

Of the ones that have worked, I've noted that I do need to see the lower limit a bit lower to ensure that none of the ones that want to flicker/sputter cause grief when they should be off. You don't want to dim to zero or when your up cue hits, there will be a delay. You probably have to slow down the dim/raise rates since you are now compressing everything in that last 30%, if you want it to feel traditional.

What I wish would happen is to abandon conventional dimmers and LEDs that screw into 120V sockets and just go to straight up LEDs and variable output low-voltage DC supplies so that you could dim the LED over its entire range. Make the dimmer such that it knows that characteristics of LEDs so that 50% level is really 50% lumen output too and so forth.

Has anyone tried using dimmable LEDs with Variac dimmers like "Luxtrol" from Superior Electric? I wonder if they would do better with a variac than a chopped up waveform. Or would their internal circuits just wig out over the lowering amplitude.

I'd think there would be enough of a market out there for people that want a zero output light that someone would start making/advertising them for theatrical use. Heck, even home-theatres might want such a thing (I know I do).

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Gordon McLeod
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 - posted 03-06-2017 09:27 AM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
Idealy a LED would like a smooth dc feed and they do dim very well with a variac
that said the issue with the screw in led lamps is that they have a switch mode supply in the base a triac dimmer (leading edge)switches on at various points of the cycle and as such the switch mode supply has issues with the steep turn on
A trailing edge dimmer will dim far better but they are a very expensive device
Also if you put a 100watt incandescent lamp on the dimmer in the booth it will keep the current through the triac high enough to keep it latched

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Scott Norwood
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 - posted 03-06-2017 12:45 PM      Profile for Scott Norwood   Author's Homepage   Email Scott Norwood   Send New Private Message       Edit/Delete Post 
How do the stage lighting companies do this? ETC has some excellent PARs and lekos with LED light sources that are fully dimmable. I am sure that other companies sell similar fixtures. As mentioned above, the curve is different from tungsten lamps (and the color temperature does not become warmer when they are dimmed), but they look fine and dim properly down to 0%.

I have yet to see LED house lights that look acceptable to me when dimmed. Is this a function of cheaper LEDs and/or power supply circuits being used for house lights, or is something else the reason for this disparity?

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Carsten Kurz
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quote: Scott Norwood
How do the stage lighting companies do this?
Once you agree on a dedicated control line (in this case, DMX), it is no problem to dim LEDs with PWM. The problem with replacing incandescents on dimmers with LEDs is that there is no such control line. With DMX controlled LEDs, you have constant line voltage to the fixture, and tell the light to dim up or down through the control line.

I have found some very few of the latest filament LEDs to even work smoothly from 0 to 100% and back on our old variable voltage rheostat dimmers. But I had to test three dozen different bulbs to actually find them.

Some newer electronic dimmers (Kelmar) work nicely with dimmable standard LED bulbs.

Yes, the curve is always slightly different from incandescent, but people get used to that.

- Carsten

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Paul Mayer
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 - posted 03-06-2017 01:31 PM      Profile for Paul Mayer   Author's Homepage   Email Paul Mayer   Send New Private Message       Edit/Delete Post 
The local art house here uses strips of tiny LEDs laid out in the ceiling in the shape of a chevron. They dim very smoothly and completely to full off. I'll ask the owner, when I next see him, what they are using for their house lights and dimmers.

Guild Cinema

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Martin McCaffery
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 - posted 03-06-2017 02:43 PM      Profile for Martin McCaffery   Author's Homepage   Email Martin McCaffery   Send New Private Message       Edit/Delete Post 
We put in LED's last year to replace our fluorescent house lights (original 1941 installs).
Better than fluorescents, no where near as good as incandescents. The do not fade down/up to zero. If you search, you can find some that will get close. When I have some time and enthusiasm, I'm going to work on the timing with the curtain spots to see if I can get them to "mask" the dimming of the house lights.

FWIW: We replaced all of the lights in the building with LED's and I'm fine with those. Just never got the 100-0 dimming I was hoping for.

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Manny Montes
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quote: Gordon McLeod
Also if you put a 100watt incandescent lamp on the dimmer in the booth it will keep the current through the triac high enough to keep it latched
This is exactly what we did and it works amazingly.

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Lyle Romer
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 - posted 03-07-2017 05:35 AM      Profile for Lyle Romer   Email Lyle Romer   Send New Private Message       Edit/Delete Post 
I have Philips BR-30 LEDs in my house that dim very close to 0% in a smooth manner. I don't know if they make them anymore but they have a skinny "neck" and a flat disk as the front. The model I have has a 90+ CRI.

I've recently seen at Home Depot, LED bulbs with "warm dimming" where they change the color temperature as they dim. There was a Cree candelabra bulb on display that simulated incandescent pretty well.

If dimming performance and light quality are more important than electric savings, just go with halogen bulbs instead of LED. How much electric do LEDs save in the auditoriums? They are off most of the time. The lobby is a different story but you don't have to worry about dimming in the lobby.

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Justin Hamaker
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From: Lakeport, CA USA
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 - posted 03-07-2017 06:31 AM      Profile for Justin Hamaker   Author's Homepage   Email Justin Hamaker   Send New Private Message       Edit/Delete Post 
Lyle, it may wind up that's what we stick with. However, we are exploring the LED solution to see if it's feasible. For one thing, when you're talking about 40 bulbs, using 1/6 the power is not insignificant. We're also looking into whether the LED solution could also be powered by a battery backup for our emergency lights.

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Steve Guttag
We forgot the crackers Gromit!!!

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Though they are not cheap, MIT does have their ALF series of LED light fixtures. They are indeed low voltage (36-volt) LED fixtures that work with 1-10-volt dimmers that should dim in a uniform fashion. Even those, however, don't dim to zero. They dim to .1% and require the power to be interrupted to completely quash them.

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Leo Enticknap
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 - posted 03-07-2017 09:47 AM      Profile for Leo Enticknap   Author's Homepage   Email Leo Enticknap   Send New Private Message       Edit/Delete Post 
quote: Frank Cox
I don't know why you would have to change the bulbs so frequently. I have a Kelmar dimmer and the bulbs that I use (standard 75w floodlights) last roughly forever.
The Aero's auditorium has 36 PAR 38 recessed fittings. When they had filament bulbs in them, I'm guessing that they probably lasted around a year, but that given that they were all blowing at different times, this resulted in about a monthly ladder ritual. The LED replacements have already saved us, at a guess, around 20-30 hours in staff time, and so they've probably paid for themselves in that alone.

quote: Steve Guttag
LEDs don't dim like incandescents. It is kind of like a linear versus logarithmic taper faders. With a standard dimmer, you'll spend 70% of its range to dim the lamp about 10% and then compress the rest of the dimming in that last 30% so you need to change your upper limit and throw away that top 10% of its light. The other thing about "dimmable" lamps is that typically they are only rated to dim until 10% output and then it is all bets off from there. And even if you find a lamp that has the characteristics you like, there is no guarantee that it will remain that way on future purchases.
Thanks for the explanation. I was guessing that this had something to do with the current rectification that takes place on the board in the bulb itself.

quote: Carsten Kurz
Once you agree on a dedicated control line (in this case, DMX), it is no problem to dim LEDs with PWM. The problem with replacing incandescents on dimmers with LEDs is that there is no such control line. With DMX controlled LEDs, you have constant line voltage to the fixture, and tell the light to dim up or down through the control line.
We were given that advice when contemplating LED replacements for the Egyptian: that the only way to make the dimming look really nice is a system that does not require you to increase and decrease the AC line voltage going to the fixture. DMX was mentioned. It's a lot more expensive, and as Tarantino might put it, "pretty f***ing far from plug and play," given the need to install all that low voltage control wiring, though.

quote: Martin McCaffery
If you search, you can find some that will get close.
Agreed - not all "dimmable" E27, straight swapout LED bulbs are made equal. After experimenting with a few different ones, we decided to use these Feit Electric PAR 38 bulbs. They're not the cheapest, but they have the nicest light quality, the closest color temperature to the incandescents they replaced, and the smoothest dimming of any we've tried. The seriously chunky heatsinks mean that they shouldn't overheat and crap out, either; though so far, one has. Incidentally, we have two of them lighting the stairwell, too, which have been running 24/7 since January 2015 and are still going strong.

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