Film-Tech Forum ARCHIVE: Experiment: Replacing Xenon lamps with a LED array in an old 35mm projector

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Topic: Experiment: Replacing Xenon lamps with a LED array in an old 35mm projector

Justin Hamaker
Film God

Posts: 2253
From: Lakeport, CA USA
Registered: Jan 2004

posted 11-22-2015 06:39 PM

I don't know much about this technology, but it seems like it's getting more possible. We recently replaced the field lights at our drive-in with LEDs, and we're getting about the same light output and range as we did with a halogen bulb. I think these fixtures have a single very large LED, rather than an array.

Going in a different direction, I would think art house theatres might be able to make a deal with local cinemas to buy their used bulbs. Because of warranties and contracts, theatres are changing out bulbs at the end of their rated live, but most of these bulbs are still working just fine at 1500 hours. I'm not sure if a Ushio UXL-30SC can be directly adapted to a regular Xenon lamp house. If they can, I probably have 25-30 bulbs on my self with 1500 hours.

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Simon Wyss
Film Handler

Posts: 80
From: Basel, BS, Switzerland
Registered: Apr 2011

posted 11-23-2015 07:19 AM

Found this thread only now

As has been said the ideal light source has the form of a point. Basically a LED comes close to the ideal but the energy conversion or transmission possible in its tiny room is very limited.

The open electric discharge arc is still quite small, yet it has a very if not the very important property for cinema projection: continuous spectrum. The spectrum contains also violet and ultraviolet, that part of the energy output that can cause fluorescence with a whited screen (lime). This was an unsconsciously but nevertheless powerfully acting magnet of early cinema.

Doped carbons provide even more ultraviolet rays and spectral peaks. Pure carbons without a copper sleeve cannot be burnt at so high power values. They’re thicker, too.

Now, upon reviewing the development of motion-picture film projection optics we find the introduction of the aspheric mirror in the early 1930s. Emil Busch optical works of Rathenow, Germany, offered the Neoplan mirror in 1935. It doesn’t produce an image of the arc (with caustic) but a light hose (Lichtschlauch), an elongated constriction in which center is placed the film.

The deep ellipsoidal mirror in conjunction with the xenon arc lamp is not more efficient.

What I find interesting is that solid-state technology almost always finds a dead end. Most efficient and at the same time most economic processes involve consumption of materials, cheap renewable materials. Manufacture of cinema carbon rods as well as their use is simpler and cheaper than all other technology and due to the form of the xenon arc between tungsten electrodes the brightest area of the carbon arc is more compact and more uniform.

I don’t think that there has ever been anything technically better and a more beautiful theatrical light than that of the High Intensity carbon arc in conjunction with an aspheric mirror and a matched lens.

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Jack Ondracek
Film God

Posts: 2348
From: Port Orchard, WA, USA
Registered: Oct 2002

posted 11-23-2015 09:22 AM

quote:
We recently replaced the field lights at our drive-in with LEDs,

As have we, Justin. We're also getting ready to replace our readerboard lights with LED. In our case, it looks like we're getting about double the light with the Cooper fixtures that we were with the old halogen lamps... all for a fraction of the wattage.

This doesn't do much for the topic here, but at least in this case, LEDs have found another worthwhile purpose.

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