Film-Tech Forum ARCHIVE: Can Automation Control LED Lighting?

This is topic Can Automation Control LED Lighting? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=008528

Posted by Tom Doyle (Member # 1474) on 02-26-2007, 02:15 AM:

We have some cove lighting in our main auditorium. The incandescent bulbs are very difficult to change. We were thinking about replacing them with LED lighting. However, the installer we talked to suggested a 12v system that would be controlled by a manual dimmer. I'd rather have them tied into the automation. Any suggestions? (The automation is a Xetron Maxi-12XPC.)

Posted by Gordon McLeod (Member # 33) on 02-26-2007, 07:21 AM:

Some solid state dimmers do not like reactive loads of a transformer so be carefull

Posted by Mark Gulbrandsen (Member # 72) on 02-26-2007, 08:51 AM:

Gord is correct about being careful what dimmer to use. There ARE dimmers made to control things like Buck Boost transformers and the like safely. Years ago on one job I saw a buck boost transformer explode from being driven from an incorrect dimmer(I warned the electrician too!).

The other way to do this is to use a manual dimmer and give your lights a preset level. Then just use a set of contacts... or an internal set to drive an external contactor to kill the power to that manual dimmer during the show. Either way will work the latter is the least expensive route.

Mark

Posted by Jeff Taylor (Member # 443) on 02-26-2007, 10:04 AM:

Of course there are standard base 120v screw in LED conversion lamps. I think they equate to a 20-25w light output. I know the historic restored theater in downtown Buffalo has installed them in the marquee with good results. I'm not sure how they'd react to a dimmer, and they're not cheap, but it might be an alternative. Google The LED Store and you can see what's available.

Posted by Frank Angel (Member # 248) on 02-26-2007, 10:48 AM:

How is the LED dimmer that will control the LED lights manually controlled? Whatever that machanical device is (a pot, a lever of some sort), the trick is simply to mechanically interface it to your automation. That might mean connecting its shaft to a small geared reversable DC motor that when activated in either rotation will turn the shaft of that manual LED dimmer control. It might be that manual LED dimmer control uses a simple variable voltage thru a pot to drive its dimmer circuit. If that is the case, it could easily be controlled by the exisiting dimmer system by knocking down and rectifying, if need be, the existing dimmer system's 120vac channel output to whatever the LED dimmer control voltage needs to be - 12vdc, 24vdc, etc. It might take some doing, but I wouldn't give up on it if the LED lighting really fulfills a need. ANYTHING can be automated, you just need to configure a workable interface.

BTW those direct conversion LEDs Jay's talking about don't like dimmers either. We even had trouble with compact florescents which claimed right on the box that they were OK to use in dimmer circuits. Their life seemed to be cut in half when run under dimming conditions. Many of them failed within weeks. The small solid-state rectifiers in both those LED and CF direct replacement units REALLY don't like dimmers.

Plus, we have a bunch of direct replacement LEDs for area lighting in our office and we found they loose light output considerably with age, something we hadn't planned on.

You might want to try a simpler solution -- try using extended life incandescant bulbs and then set your dimmer presets so that those hard to reach circuits are never run to full voltage. A simple precaution like that could help extend the life of the incandescents so you wouldn't have to change them that often.

Posted by Jack Ondracek (Member # 1466) on 02-26-2007, 11:40 AM:

quote: Frank Angel
You might want to try a simpler solution -- try using extended life incandescant bulbs and then set your dimmer presets so that those hard to reach circuits are never run to full voltage.

Yep.
Some of those 8,000 hour marker lights they use on radio towers are good for 5+ years.

Posted by Joel N. Weber II (Member # 3530) on 02-26-2007, 10:47 PM:

I'm under the impression that the efficient way to dim an LED is with pulse width modulation: that is, you have a circuit to turn the power on and off rapidly, and by varying the ratio of the on to the off, you control the intensity of the light.

If you've got a set of LEDs that are set up to cope with pulse width modulation, I imagine it's not that hard for someone to build a controller that would have several inputs to select presets. This might work well for controlling a 12V system.

On the other hand, how thick do the wires need to be on a 12V system? The total light output is usually very roughly proportional to the voltage times the current, which means that lowering the voltage requires greater current, and greater current implies thicker wires.

I think an individual LED (for most colors) typically has a voltage drop of about 1.5V; you can put multiple LEDs in series if you have enough voltage, and there's typically also a resistor in series to limit the current so that the LEDs don't overheat and stop working.

Posted by Tom Doyle (Member # 1474) on 03-03-2007, 01:55 PM:

I should give a little more detail about our lights. The cove has a 'lip' that prevents us from using a pole changer. The bulbs are too high for a ladder - we need to remove seats and then use scaffolding to change them. We don't want to do this very often. The lowest quote we got from an outside source to replace the bulbs was something like $2500.

The installer we were talking to for LEDs is a professional, so I'd hope he uses the correct kind of dimmer. He told me that the power supply would be rack mounted and it would power 22 amps worth of 'light-bar' style LEDs. He wasn't aware of anything that would interface with the automation. I do like the suggestions to build a mechanical or electrical controller, and I'd work on that if we go with the LEDs. But, does anyone here use automated LEDs?

quote: Jack Ondracek
Some of those 8,000 hour marker lights they use on radio towers are good for 5+ years.

I'd love to know more about these. We use 130V bulbs in the auditorium lighting and they aren't as good as we'd like. I've found some long-life bulbs that sound pretty good here:
http://216.86.216.207/decadeabulb.html
but I haven't heard anything about them otherwise. Once some of these cove bulbs go out, it looks like crap and they all need to get changed. What bulbs do you guys use in these 'must not fail' places?

Posted by Dominic Espinosa (Member # 2122) on 03-03-2007, 02:20 PM:

David Tyson Lighting sells a variety of bulbs that are rated for 20,000 hours.
We use some of the A19 types like this for anything we can. I've never changed one of them out after installing it. It's been 3+ years for some of them that I am aware of.

http://www.bulbtown.com/20_000_Hour_Light_Bulbs_s/1.htm