House LED lights flickering
The lights in our cinema flicker when set to any state other than full on (or off obviously). This means we can't have low lights come up during the credits. At present we run shows with the lights fully off, for the entirety of the show until turning them on fully at the very end of the feature. It's not great. I'm told by our service tech that this is a common problem. Does anyone else experience this?
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The solution depends on the type of installation you currently have. You're in the UK, so you should have 220V mains per phase, just like mainland Europe. If your house lightning is on 220V AC, then an old-school voltage dimmer will not work as intended, unless you buy very specific LEDs that have built-in transformers that can handle voltage-based dimming. Even then, the situation will not be ideal. If you buy generic 220V LED bulbs without dimming support and you put them on an old-school dimming circuit, you'll get the typical flashing/strobing effect.
The best solution would be to invest in a LED installment that uses LED drivers that support dimming. -
Thanks so much for that Marcel, that's excellent information, cheers!
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If your dimmers are ETC brand like in traditional theatre houses they make LED compatable modules you can swap in to improve the LED curve and response, success may still depend on the variety of LED bulbs/fixtures deployed.Comment
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It is also worth noting that dimming LED fixtures on a voltage or resistance dimmer can kill them prematurely too. Our work lights circuit in our small theatre had about half die in 3 years due to doing this without considering the impacts.Comment
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I've encountered ETC dimmers (and other DMX-based house light systems) in university auditoria, mixed use venues, and that sort of place; but not in regular movie theaters.
Not all "dimmable" LED bulbs designed as screw-in (or in the UK, where bayonet-type caps are used rather than E27s, push and twist in) replacements for old school filament bulbs are made equal. Some dim more smoothly and last longer than others, and the better quality ones have a lower point before the light goes out altogether, too. For our most popular model of dimmer, the ALMS-20, wr keep a list of specific bulb models that we know dim well, based on our own testing and customers' reported experiences. We also keep a list of models that have been reported as problematic. Both are internal documents - we don't want to get into either endorsing or disparaging third party products - but when a customer reports flickering or uneven dimming issues, my first response is to ask what make and model of bulb is involved. 99 times out of 100, swapping them for one that we know works well fixes the problem. If there are a large number of bulbs involved and swapping them would be a major expense (or a logistical problem due to the height of the ceiling), replacing one bulb on each circuit was a 25 or 40 watt incandescent often fixes the issue.Comment
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Leo is on the money. We also have a preferred lamp list. Even ones with "dimmable" on the label don't always do well. It seems that transients on the very long wire runs in cinemas is part of the problem, those lamps often do fairly well in a house.
They don't dim to blackout smoothly, it's very rare to see that - just get pretty dim then go off. On is similar, they come on fairly bright (and not all at once in an array) rather than dim up from off smoothly.
Adding a resistor in the dimmed circuit pulling maybe 20 watts at full power may help. Putting in one incandescent bulb in an array is about the same but works better, maybe due to the low cold resistance of the filament? For some reason that bulb has a short life in my experience.
Kelmar here adds the resistor as standard now, and also sells an LED output accessory: I don't know what that does.
Our only 100% success for ideal dimming with LEDs has been on new installations using powered luminaires with 0-10VDC or DMX control. That is rarely possible in existing auditoria, requiring the addition of all the control wiring. If someone makes a light controllable by something like DMX over powerline, that could work. I have not seen wifi "smart" bulbs that I could recommend for cinema house lighting.Comment
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Excellent info, thanks for this guys.Comment
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When I moved up into a larger apartment in my building several years ago, I picked
up some "KAILIN" LED bulbs in Chinatown, that were made in China (naturally!)
and even though the broken English on the box says nothing about them being
dimmable, I was very surprised when I discovered that not only did they work with
the dimmers in my home, but they behaved exactly as an incandescent bulb, and
smoothly went from "full on" to "full off" without the usual sudden cut-off or turn-on
plateaus. It took me a while to realize that they weren't doing this by using any secret
circuitry- - the trick was that the bulbs apparently use a very slow responding phosphor.
So, although the internal UV LED (or whatever they are using) still does a 'cut off' when
the dimmer reaches a certain level, It still takes the light from the phosphors almost
another 1.5sec or more to completely decay, giving the appearance of a bulb that dims
smoothly from 100% brightness down to 0% off. A similar thing happens when dimming-up.
I bought awholebuncha them at the time, to put them in all the dimmable fixtures in my
apartment. I recommended them to a friend, and he could not find them at the store
where I bought them, however he was able to get some at a big lighting store here in
S.F. Unfortunately, that store recently closed, after being in business for many years.
I don't know if they are sold anywhere online. I've never tried them at a theater, but if
I could find a source I might want to try them in at least one of our smaller auditoriums
to see how they work in there, but they're almost impossible to find now.Comment
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The most annoying thing I have found is that many times we or someone has found a bulb that seemed to work OK but then you go get more and they act completely different. We have had people do something like say convert one auditorium in the complex and get workable results so then after days, weeks, or months go back to the same store or supplier and get enough to do the whole complex and half of those don't perform the same as the first batch.
Other than the 'curve' and sensitivity I have not really seen any difference in performance with any of the common to cinema dimmers. Some do seem to be worse with some bulbs some of the time and others don't seem to make any difference, even when they are mixed in the same complex. Some dimmers the curve and sensitivity can be a problem especially because we are often trying to ride that fine line of minimum dim without dropping or flickering.
Dave's note about the characteristic of a filament vs a typical resistor is interesting as well as the observation of it not lasting long. I wonder if there is maybe some noise or harmonics going on rattling the filament? The longer wires could also be part of that, harmonics getting back into the leds and helping them to an early death too? I will have to ask sites that have that if they are having to replace those very often. Its common to see a socket mounted on or next to the dimmer in the booth with that bulb in it.
I have sites with the Kelmar module on both Kelmar and other dimmers and they don't seem to really make a for sure difference either. My understanding is that module was designed to complement a specific bulb design that was thought to become common but for one reason or another (likely cost) that design didn't really catch on. I'm thinking this design was pretty early on when a single bulb had a big hunk of metal heat sync on it and cost like $30+ each. When is the last time you seen a bulb with any significant metal in it? I have a few around my house that are that old and still work but don't ever remember seeing them in theaters.
Recently I had to replace my outdoor yard lights and was kinda surprised when they arrived that they were 0-10. Wasn't looking for and don't really need that feature but just for fun tried it out on the bench with my bench supply and they have a nice curve and at least with the 2 I had stay in sync nicely. At exactly 1.0 volts they are at their minimum brightness (which is likely still too bright for typical cinema use) and 0.9 they cleanly drop out. 1.0 cleanly come back on with no burst or flash. Same thing even if you turn the power on and off with the 0-10 in a steady state. 0.9 they don't do anything and 1.0 they come on to that dim.
The clean drop is nice because if you do have to drop them you don't need the extra relays to do that. Many 0-10 stuff just goes to the minimum with a minimum signal so if you need em out you have to have the extra control step of killing the power. MIT does or did have a 0-10 dimmer that had both the 0-10 outputs as well as dry contacts you could use to drive relays. Jnior's analog control program also had the provision to operate a relay as part of the dimming sequence. Really annoying that a cheapo yard light acts that way. Could likely spend way more on something marketed as dimming and it would not perform that well. I also wonder how they would perform with more in series and longer wire. I would hope 0-10 would not be a problem with long wires but I suppose its all in how well they did or didn't care about the standard.Comment
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[QUOTE=Leo Enticknap;n53444]I've encountered ETC dimmers (and other DMX-based house light systems) in university auditoria, mixed use venues, and that sort of place; but not in regular movie theaters.
/QUOTE]
Yes, Schools, and architectural sites, Utah State Capitol Building, and lots in Utah, like every single school's auditorium. The dealer I first worked for was a Strand and Leviton (Colortran) dealer. The Strands were amazingly easy to work on but not sure they are still in business these days as they were bought out a couple times in the mid 2000's.Comment
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I agree that a single incandescent lamp being driven by the phase control dimmer can improve LED lamp operation. Most phase control dimmers have an RC snubber across the triac or SCR. When the triac or SCR is off, or very close to off, the current through the snubber slowly charges the power supply capacitor in the lamp until it reaches a voltage where the lamp comes on and quickly discharges the capacitor. The process then repeats again. The incandescent lamp load keeps this voltage from building up due to the low snubber current.
Harold
Product designer for https://www.dovesystems.com/ 30 years ago...Comment
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