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This topic comprises 2 pages: 1 2
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Topic: Auditorium Dimmer with LEDs
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Leo Enticknap
Film God
Posts: 7474
From: Loma Linda, CA
Registered: Jul 2000
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posted 03-05-2017 11:52 PM
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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Leo Enticknap
Film God
Posts: 7474
From: Loma Linda, CA
Registered: Jul 2000
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posted 03-07-2017 09:47 AM
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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