Film-Tech Forum ARCHIVE: Xenon Bulb wire

This is topic Xenon Bulb wire in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Daniel W. Skeen (Member # 4269) on 09-06-2007, 10:19 PM:

What is the purpose of the small "shorting" wire on Xenon bulbs? It goes from anode to cathode, across the glass bulb. Should it be left on or removed when the bulb is installed?

Posted by Monte L Fullmer (Member # 2797) on 09-07-2007, 12:14 AM:

That wire aids in ignition since it acts like a small capacitor to get the spark across the electrodes inside.

Ususally it's best to leave that wire on if necessary. It can be taken off, but bulb ignition might be harder to accomplish.

Posted by John Walsh (Member # 168) on 09-07-2007, 07:40 AM:

Yes, you should leave it on; as Monte said, it helps with ignition. It actually does not connect anode to cathode, it just connects at one end. If it connected, it would short out the power supply! It's made of nichrome, not regular copper since copper would burn up quickly.

Posted by Stephen Furley (Member # 1277) on 09-07-2007, 08:04 AM:

A similar ignition aid is also used on some less exotic lamp types. Some Philips lamps have printed onto the outside of the arc tube a ring at each end, with a thin line along one side, jioning the two rings. I first saw it on SDW-T 'White SON' lamps, a lamp type never common in America, and tending to be replaced here in Europe by compact ceramic metal halide now. These lamps operate at a higher pressure than normal SON lamps, and the use of this device enables them to strike with a lower ignition Voltage than would otherwise be the case. They're suposed to be used with special control gear, but I can just about get one to strike with a 2.3kV SON ignitor.

Philips now use this device on regular SON lamps as well. They've started using a higher proportion of xenon in the buffer gas fill, which would otherwise raise the ignition Voltage needed. There's a pucture of it here

Posted by Mark Gulbrandsen (Member # 72) on 09-07-2007, 08:45 AM:

quote: Monte L Fullmer
That wire aids in ignition since it acts like a small capacitor to get the spark across the electrodes inside.

Monte... Its not a capacitor! All it does is aid in ionizing the xenon gas within the bulb to insure good ignition. The wire needs to be there and if is damaged can usually be replaced with wire that can be had from any one of the lamp manufacturers.

Mark

Posted by Louis Bornwasser (Member # 3063) on 09-07-2007, 10:52 AM:

The exception is the XeLamp by LP Associates. The wire MUST BE removed if the bulb is to ignite in the operating position. Louis (It arcs over to the reflector.)

Posted by Dan Reiter (Member # 1386) on 09-07-2007, 12:35 PM:

Also to help de-mystify:

The ignition wire is usually connected to the positive end of the lamp via the end fitting, ties in a loop around the lamp body just before the envelope, travels over the envelope, and ends in another loop on the other end of the envelope. This provides a positive charge to help the arc jump from Cathode to Anode during ignition, as the igniter is usually connected in series on the negative end of the lamp.

As all have said before, an ignition aid.

Louis did bring up one note. If the opening of the reflector where the lamp goes through is small, and close to the lamp body, there is the possibility of ignition arc-over on a hard-striking lamp via the ignition wire. That, in addition to restricted cooling air flow, will shorten lamp life.

Posted by Monte L Fullmer (Member # 2797) on 09-07-2007, 01:36 PM:

quote: Dan Reiter
as the igniter is usually connected in series on the negative end of the lamp.

..which brings up the interesting question on this one: What about the positive connected ignitors like the Christie lamphouses and consoles? Granted, this action still does work well with these consoles, but still interesting to hear on this one.

Posted by Mark Gulbrandsen (Member # 72) on 09-07-2007, 06:55 PM:

quote: Dan Reiter
Louis did bring up one note. If the opening of the reflector where the lamp goes through is small, and close to the lamp body, there is the possibility of ignition arc-over on a hard-striking lamp via the ignition wire. That, in addition to restricted cooling air flow, will shorten lamp life.

There are quite a few XeLamps on my service routes and I've found that the use of a lamp with an oval shaped glass envelope(Ushio,Christie) eliminates the problem of arc over to the XeLamp reflector.

Mark

Posted by Gordon McLeod (Member # 33) on 09-07-2007, 09:35 PM:

The older Zeneith 2000H and 3000H had some issues with the nichrome wire

Posted by Bryan M. Montgomery (Member # 4412) on 09-08-2007, 01:00 AM:

We had to remove the ignition wire on bulbs used in our Zeniths years ago, otherwise they would not strike.

Posted by Tim Reed (Member # 137) on 09-08-2007, 01:32 PM:

The Cinemeccanicas were notorious for that.

Posted by Michael Schaffer (Member # 1204) on 09-08-2007, 05:21 PM:

quote: Dan Reiter
This provides a positive charge to help the arc jump from Cathode to Anode during ignition

How? I can see how the wire "relocates" the positively charged portions of the lamp closer to the anode, but on the outside of the bulb. How exactly does this aid the discharge across the arc gap inside?

Posted by Louis Bornwasser (Member # 3063) on 09-08-2007, 05:27 PM:

This is a "gimmick" capacitor. Louis

Posted by Gordon McLeod (Member # 33) on 09-08-2007, 07:26 PM:

Kneisley used to have a small beaded chain that one hung on the lamp to help do the same

Posted by Frank Angel (Member # 248) on 09-09-2007, 02:48 PM:

the Osram lamps that I've got, 4500W have no wire. They ignite fine. What's that about?

Posted by Floyd Justin Newton (Member # 1316) on 09-09-2007, 04:00 PM:

I'll tell 'ya that's about, Frank. Are you holding the bulb with your bare hand when you ignite it??? Just kidding!

Posted by John Hawkinson (Member # 1135) on 09-09-2007, 07:31 PM:

quote: Osram's XBO Theatre Applications Guide

Ignition Wire

The ignition wire is a thin, thermostable iron-nickel wire slung from one lamp neck to the other and - depending on lamp type - sometimes continued as far as the base sleeve. Its existence makes igniting the lamp easier, especially when rectifiers and igniters have diminished in efficiency with increasing age. Its function is twofold: firstly it distorts the high-voltage electrical field applied to ignite the lamp, producing inhomogeneities which cause peaks in the field distribution, a condition favorable to sparkover. Secondly, partial discharges take place on it, these can knock electrons from the cathode by a photoelectric effect, and these in turn initiate the discharge

--jhawk

Posted by Phil Hill (Member # 371) on 09-09-2007, 07:41 PM:

Thanks jhawk for posting all that gobbledegook... Mark and Louis said it BEST in their responses!

Posted by Michael Schaffer (Member # 1204) on 09-09-2007, 08:19 PM:

Actually I think what it says in the Osram text makes a lot of sense. That is what I had been asking: not what the "function" of the wire is, we all know that, but what its effects are from a physics point of view (so that one can "picture" what is going on). I don't quite understand yet how the photoelectric effect fits into "secondly" though.

Posted by Frank Angel (Member # 248) on 09-09-2007, 10:33 PM:

Yah, yah, yah, but these are Osram bulbs that I've got and they don't have any freakin wire. In fact, Osram has a video all bout how awesome their bulbs are and how they explode so nicely, and I listen very carefully to the pitch man and he definately says that the wire is on SOME bults. Could it be the wattage -- that the higher wattage bulbs don't need them as much? Ours are 4500w. I'm just guessing, based on the inhomogeneity peaks and phototronic metaphysical structure of the wadayacallit.

Posted by Mark Gulbrandsen (Member # 72) on 09-10-2007, 09:06 AM:

quote: Frank Angel
the Osram lamps that I've got, 4500W have no wire. They ignite fine. What's that about?

HA.... They might not ignite too well when you get some hours piled on them. Thats when things begin to get difficult with alot of lamps.

MAra

Posted by Dave Macaulay (Member # 813) on 09-10-2007, 11:08 AM:

I don't know how the wire would make any light, but there is a photoelectric effect on ionizing gases. It's common to see a neon light that won't work in the dark but "ignites" fine while a little external light hits it.

Posted by Michael Schaffer (Member # 1204) on 09-10-2007, 03:41 PM:

Maybe the wire glows briefly when high voltage is applied to the lamp (and maybe only in non-visible parts of the spectrum, but then none of us has ever actually looked at the wire and the lamp when they ignite), since "partial discharges" take place across it.

Posted by Bill Enos (Member # 440) on 09-11-2007, 06:59 PM:

It's done by PFM

Posted by Mark Gulbrandsen (Member # 72) on 09-12-2007, 08:40 AM:

Bill.... I think you ment to say "its done by PMS".

Posted by Bill Enos (Member # 440) on 09-12-2007, 12:21 PM:

Pure F------G Magic