How-to build a light box for theatre?
July 16, 2007 6:55 PM   Subscribe

I need some pointers on making a light box. Now, before you point toward some other posts about either an all-white surround for photography or a means of defeating winter-time depression, I should point out that I'm needing to make a light box for theatre ...

In other words, I need a little help with building a box with 4 or 5 dual electrical sockets along the front, dimmer switches or sliders on top and a power cord coming out the side. In other words, a central console to control lights for a theatrical production, preferably one that is tolerant of being outdoors. I've borrowed them to use before for outdoor productions, but I need to make one for our company to use in a month or two.

They're rather common in community theatre, but designs or instructions are hard to come by through a search (the whole "light box" disambiguation thing, I suppose). So if anyone can point me in the right direction or give me enough basics to prevent an electrical incident, I'd appreciate it.
posted by grabbingsand to Media & Arts (8 answers total)
If you have a small budget, you can outfit yourself with 8 channels of dimmer and 16 channels of DMX controller for around $300:

Cheapo American DJ Package

If you insist on building it yourself I can provide pointers, but only if I know more about your need. How many fixtures and how many watts per fixture do you plan on running from this box? What kind of power do you expect to have available to you at the site (125V 15A circuits? 125V 20A? 125V 30A? 220V?

Building the dimmers into the control box isn't a good way to do things because all of your power has to be home-runs. With the dimmers outboard, like in the linked kit above, you can place the dimmers closer to the instruments, and split dimmers to multiple power circuits more easily.

Also, if you build it yourself it probably won't meet UL code, so expect visits with the Fire Marshal to be sketchy.
posted by tomierna at 7:30 PM on July 16, 2007

You want to be asking the fine folks of the Stagecraft Mailing List: Truly a great resource for anything related to theatrical technology.

And as tomierna says, this is really something where if you have to ask, you probably want to buy; theatrical fires are bad...
posted by zachlipton at 8:11 PM on July 16, 2007

Only a qualified electrician should be building something like this.

A qualified electrician would know how to build something like this.

I'm guessing you're not a qualified electrician.

Find one.
posted by dirtynumbangelboy at 4:04 AM on July 17, 2007

We are using outdoor grade lighting, because it's an outdoor production, and we are not in the position to spend a ton of money. We use a couple of these - maybe three - and one or two of the next size larger ones, as well as one or two of the small, single lamp, sit-on-the-ground versions. We are not indoors and in 18 months have not started a fire. We have in fact only thrown one breaker one time, and that's with all our lights, speakers, and sound equiptment set up. We have an outside powersource set up by electricians - it looks like your standard outside the house heavy duty outlet but I don't know more than that at this instant.

We know the circuits must be set up in parallel to one another and not in series. This is a very common thing to build in community theatre, so I'm very sorry for the snark displayed above; this is not a stupid question. Thanks to the first two answerers - we will check out the stage craft mailing list; unfortunately, our lighting situation is dictated by necessity and not by what we would want, so the DJ set up above won't work for us (but if you have experience or suggestions setting up such things to survive the outdoors, we certainly welcome it).
posted by Medieval Maven at 6:43 AM on July 17, 2007

That's a little more information, but still not enough to calculate amperage ratings.

An electrician would need to know how many lamps (bulbs) you plan on plugging into this thing, and how many watts each lamp is.

It would be good to know exactly how many individual dimmers you'd need as well - how many light fixtures do you need under individual control?

Also, it would be necessary to know if the "powersource" contained one or more circuits. Is it a single pair of outlets? If it's more than one pair of outlets, do you know if those pairs of outlets are each connected to a breaker? Or, (best case), is it a power distribution drop where a relatively thick cable (or set of cables) terminates at a box with a bunch of breakers and a bunch of power outlets?

Household wall dimmers (which is what you'd be using if you built it yourself) are typically rated for 600 watts. A typical 15 amp circuit can support, at most, three of these (1800 watts total). The lights you linked to come in several watt ratings - some are 1000 watts (2x500 watt bulbs), and some are 600 watts (2x300 watt bulbs).

The cheapest 600 watt household dimmers I've found are $12 each. There are very few rated for 1000 watts (what you'd need for the 2x500 watt fixtures), and they are around $50 each. They're also rocker-style electronic, not sliders, so they wouldn't be as simple to accurately operate for theater.

Parts alone, you are already pushing $150 to do it within ratings. That doesn't include the case, the wire, the plugs - that's just for the household dimmers.

If you expect to be able to build this box without risk of fire, and without risk of throwing breakers, you will absolutely need to know exactly how many bulbs and how many watts each. Then, you'd need to build a device that might have multiple 15 Amp inputs, each going to a set of dimmers, each powering a set of outlets.
posted by tomierna at 9:11 AM on July 17, 2007

I can't speak with any certatinty to the outlet that was installed for our use, unfortunately. It comes directly off the outdoor breaker box as I recall (we are on this site 2x per year and unfortunately it's been 6-8 weeks since I last dealt with this place).

We will use up to four of the 500x2 lights, and all other lights used can/will be smaller (ie, singles). We don't mind spending *some* money on the light box because 1) our lighting situation is what it is, and these will be our lights. We are not going to get an outdoor stage at this place; 2) we are engaged to perform there for at least three more shows, and we are tired of lights being a pain in the ass.
posted by Medieval Maven at 9:29 AM on July 17, 2007

Seriously - speaking as somebody who's built three or four of these using wall dimmers, buy a commercial DMX pack. Even if you spend more initially, you'll save more in the long run.
If you cheap out on everything else, you can probably hit the same target. Here's some ideas for getting everything else cheap:
  • Make a DMX cable for yourself with Cat-5 or mic cable instead of buying something special. (Pin 1 is ground, 2 and 3 need to match, 4 and 5 are not connected) No, it's not spec, and you probably don't want to use 500' runs or anything.
  • Put the pack by the lights and save yourself a fortune in crappy extension cords that frequently come undone, lose their insulation to chair legs and shock patrons, get you sued, or eat up half your power before it gets to the lights.
  • Dust off some POS PC and use a soft console and DMX adapter: DMX4Linux would provide some good, cheap choices - Contact your local Linux User's Group for help with setting it up if you don't have a pet geek yet. might also be good.
Seriously - If you're going to cut corners, do it on the low voltage side where it won't kill the operator or bystanders.
posted by Orb2069 at 9:35 AM on July 17, 2007

In case my previous post wasn't clear enough, I'm trying to dissuade you from building this yourself.

You will likely spend a good $150 in parts and a bunch of time for a potentially unsafe, definitely UL-taunting, barely adequate solution.

For $300, you will get two dimmers with 4 channels each, plus a light board which will allow you to assign faders to multiple channels and do scenes and such. It will be extendable by adding more dimmer packs and daisy-chaining XLR. The package I linked to uses standard 3-pin XLR and comes with 2 - 25' runs of it.

I've have built home-made dimmer boxes in the past. They served their purpose, but they were replaced rather quickly with real equipment once we could afford it. If you can scrape the money together now, do yourselves a favor and buy the real stuff instead.

Lastly, you say you'll have at least 4000 watts of lights (4 units, 2 fixtures, 500 watts per lamp) plus additional lights. You will not be able to power this much from even two 15 Amp circuits. You'll need at least two 20 Amp circuits. Not only that, but the dimmers in the linked kit only handle 500 watts per channel, so you'd be well advised to re-wire the dual lights so that each lamp has its' own Edison plug to go to the dimmer. If you have any extra lights past the 4 1000 Watt units, you'll want a third dimmer pack.
posted by tomierna at 2:56 PM on July 17, 2007

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