Theatre seeking modified xenon or comparable- saw larryk12 light

[H.M.Bullitt]

I am a designer for a shadow puppet theatre. We are seeking better technology but are ignorant. A 350 watt xenon short arc bulb was recommended to us. They seem rare, expensive and high maintenance. Can anyone educate me about what might have a similar output and color, cheaper and easier. There is about 10-20 feet, depending, between the screen and where we would place the fixture. We would remove the reflector and replace it with flat black to make the shadow edges crisp at every distance. To see another company's homemade light, go to flickr and search keyword shadowlight. We have regular U.S. house voltage, and need the light to be able to dim on a dmx controller or a standard home ext cord dimmer, or other method I don't know about. Can anyone offer advice? Thanks, Hank.

 

[mahoney]

Short Arc Xenon bulbs should not be used bare. And Xenon fixtures are expensive. I would suggest getting an old theatrical or film Fresnel light fixture (heck, a new one is about $75 or so) and removing the lens and reflector. This gives you a nice sturdy housing with a way to mount it. These use a halogen lamp, typically 500 or 750 watts. It is unsafe to run these lamps bare as well (without something between you and the lamp) so in the theater we sometimes use metal mesh like hardware cloth in place of the lens. For your application I would go to a glass shop and get a tempered glass lens made. An electrician could wire up a household dimmer with a 1000 watt rating to an outlet box with a power cord, or you could buy a small 1000 watt dimmer (like DJs use) that could be controlled by DMX

 

[lctorana]

How many lumens do you need?

(I was wondering if a cheap hardware-store 500W halogen floodlight might do the trick...)

 

[H.M.Bullitt]

Thanks.
A flood does not work. A small arc or filament is needed without a reflector to create an even crisp shadow, regardless of how far the object is to the lamp.
I have tried using a variety of theatre instruments but they were never right.
I think you are on to something with taking the lens out of a fresnel. I stupidly used the fresnel lens. But it seems like the throw distance wasn't enough. I was using someone elses stuff, so I couldn't futz with it too much. That could work.
I don't know how many lumens. It would be easier if I did. Where can I find out what the luman output of a 300w short arc xenon bulb is.

 

[lctorana]

No reflector?

Because otherwise, the PAR36 GE DWE 650W "Blinder" is cheap, insanely bright and mounts in a cheap, standard PAR can.

I know it's just plain incan, but for a genuine, bona fide, stage lighting solution, it doesn't come much cheaper than that. You might get away with the whole package for under $100 installed.

 

[mudman cj]

Short Arc Xenon bulbs typically have efficiencies of anywhere from 25-40 lumens/watt, but that is quite a range of 7500-12000 lumens, so I don't know if that helps at all.

 

[lctorana]

OK, the 650W Blinder shoud be nearly in the right lumen range...

 

[mahoney]

The fresnel without the lens and reflector will work for this effect, I've used it for similar effects. The main problem is that without the reflector, a lot of the light coming off the filament is wasted inside the body of the instrument. The lumens rating will depend on the lamp your fresnel uses (for example a BTL (500 watt) is rated 11,000 lumens) but it's kind of irrelevant because probably 70-80% of the light is not making it out of the instrument body. So try using the reflector, if you are far enough away from the instrument it will still work and it will vastly improve light output.

 

[mudman cj]

I think I understand the issue with reflectors. They tend to be large in order to make use of more of the light, but the larger the reflector, the further you get from a point source of light. It is this deviation from a point-like source that causes blurring of edges. So, you may be able to use a small reflector in order to greatly improve the usable proportion of light (compared to no reflector) without deviating too far from a point source and losing those sharp edges. As mentioned, the ideal size will depend upon the distance to the screen.

And in case even a small reflector still blurs edges too much, wouldn't a simple mirror right behind the bulb work to nearly double the usable light without changing the source location? As long as the bulb is small then you would still effectively have the light coming from a point, but as the glass envelope increases in size you can see from a ray tracing diagram that shadows off to the sides of the screen would get increasingly blurry.

 

[LukeA]

I think I understand the issue with reflectors. They tend to be large in order to make use of more of the light, but the larger the reflector, the further you get from a point source of light. It is this deviation from a point-like source that causes blurring of edges. So, you may be able to use a small reflector in order to greatly improve the usable proportion of light (compared to no reflector) without deviating too far from a point source and losing those sharp edges. As mentioned, the ideal size will depend upon the distance to the screen.

And in case even a small reflector still blurs edges too much, wouldn't a simple mirror right behind the bulb work to nearly double the usable light without changing the source location? As long as the bulb is small then you would still effectively have the light coming from a point, but as the glass envelope increases in size you can see from a ray tracing diagram that shadows off to the sides of the screen would get increasingly blurry.

A flat mirror will give two sources.

An ellipsoidal reflector will improve output while still appearing as a point source.

 

[snarfer]

If you are not using a lens a regular old spherical reflector will be just fine. We do this all the time on movie sets. Just pop off the fresnel for a wide beam with crisp shadows. Sometimes the reflector is all covered in crud or burnt up and you get weird colors, then you replace the reflector and it's all good.

If you do remove the fresnel from an older theatrical style lamp, please be careful. Often there will be ring of white fiber around the edges of the lens. That could very well be pure asbestos!

If you want to get really cheap a 300 watt MR-16 with built-in reflector would probably be enough. Just buy a socket, screw it to a piece of plywood, plug it into a 650 watt household dimmer. Use some wire nuts and lots of tape for DIY style points.

If you really want to try the projection lamp approach, try googling "DIY projector." There are companies that sell kits for building your own 400 watt HMI projector. Or you could buy a 1200 watt spotlight, or... there are so many alternative approaches only limited by your imagination and budget.

 

[mudman cj]

A flat mirror will give two sources.

An ellipsoidal reflector will improve output while still appearing as a point source.

Certainly an ellipsoidal reflector would be a better choice than a mirror. But if an ellipsoidal reflector is not available to the OP, why couldn't a flat mirror work well enough? True, it would produce two sources, but if used with a small bulb, the two sources would effectively be located a distance from one another equal to the distance from the filament to the bulb envelope (with the mirror against the envelope).

I don't claim to have actually tried this, and I don't know how small these bulbs can be, but until someone tells me they tried this with a small bulb and it didn't work for this application, I am not convinced that it couldn't. Forgive me for arguing what may be an irrelevant point here, but I want to respectfully suggest that this may be of some assistance to the OP.

 

[H.M.Bullitt]

Thanks, these are all useful.
What if I cut off the front of an instrument, so that not so much light is lost in th body. Will a torch cut thru an instrument? I have a welder on staff.

 

[H.M.Bullitt]

I think I have found something.
What if I put a 500 watt ps35 10000 lumen bulb in a 14 inch altman scoop. If the reflector doesn't work I can paint it black.
Any opinions on that?

 

[mahoney]

Anytime you use a reflector, particularly a not very focused one like scoops have, your "point source" becomes effectively the size of the reflector. Far enough away from the source or close enough to the shadow surface and the difference in travel distance from the filament vs. from the reflector is not so noticeable. That said, 14" is a big "point source". It's worth a try though.

Also re: cutting an instrument, that will work, but there's no point letting out any more light than will cover the back of your screen. The cool thing about a Fresnel is the "spot/flood" adjustment which allows you to move the lamp forward and back in the light body.

 

[mudman cj]

Anytime you use a reflector, particularly a not very focused one like scoops have, your "point source" becomes effectively the size of the reflector. Far enough away from the source or close enough to the shadow surface and the difference in travel distance from the filament vs. from the reflector is not so noticeable. That said, 14" is a big "point source". It's worth a try though.

That is the point I was also trying to make. One thing I found in trying to learn more about your application that applies to certain types of reflectors, such as the ellipsoidal reflector, is that they can be made more like a point source by passing the beam through an aperture at the focal point of the reflector.

 

[H.M.Bullitt]

I'm really thinking that no reflector is the way to go(or it painted black).
Here's photos of what i'm imitating.http://www.flickr.com/search/?q=shadowlight+light

 

[LukeA]

I'm really thinking that no reflector is the way to go(or it painted black).
Here's photos of what i'm imitating.http://www.flickr.com/search/?q=shadowlight+light

That is a very inefficient way to do it. And that won't throw at all.

 

[snarfer]

Painting the reflector black is not a good idea at all unless you want to roast a chicken or something in there. Removing it entirely is not a good idea either. You will end up with light reflecting back off the rest of the set and polluting your shadows with ambient light.

A spherical mirror is in fact the ideal mirror for you to use if you are not using a lens. The spherical mirror directs light back at the filament, thus creating the illusion that the reflected light is coming from the same point source.

Some people have had good luck using some sort of ikea napkin holders or something like that for a reflector. Maybe a stainless steel bowl or a measuring spoon.