Film-Tech Forum ARCHIVE: Bulb life

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

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Posted by James S. Mellen (Member # 2139) on 04-29-2005, 05:17 PM:

I have been trying to improve the brightness of a Xetron XCN-35 2kw which had an incorrectly installed heat filter. The glasses were not angled which bounced the heat back to the anode and damaged 2 bulbs (and possibly the reflector). Now that the heat filter is correct and the reflector is cleaned and polished (but probably still far from right), will the bulb life be shortened?

Also, does anyone know the correct spark gap for an S. Antonino HV igniter? This is an external spark gap. When one of the bulbs failed, the unit was on autostrike and kept trying to re-ignite the bulb until the spark gap contacts got pretty fried.

Posted by Tim Reed (Member # 137) on 04-29-2005, 05:57 PM:

quote: James S. Mellen
does anyone know the correct spark gap for an S. Antonino HV igniter?

As long as it's firing, that's all that matters. You can screw the points in a couple millimeters if you want to get back in the ballpark with the factory setting. The particular gap distance (up to the point where it doesn't fire) will only change the resonant frequency of the tank circuit it's in, and I don't know that xenon bulbs are sensitive to that. Or sound systems.

As long as the circuit oscillates (fires), you're okay.

Posted by Gordon McLeod (Member # 33) on 04-29-2005, 06:12 PM:

In some cases corona effects can happen that deter ignition if the gap is set wrong Also the ignition is much noisier than one would like

Posted by Tim Reed (Member # 137) on 04-30-2005, 10:41 PM:

With a gap great enough to cause that, I would think mis-firings would be fairly obvious. A few millimeters off one way or the other should be negligible.

Posted by Kenneth Wuepper (Member # 1174) on 05-01-2005, 07:03 AM:

The width of the spark gap determines the frequency of the current to the Tesla coil. Opening the spark gap lowers the frequency and therefore makes the filtering components less effective. Without the filtering and isolation effect of these components, the radiation of noise is greatly increased and the efficiency of the Tesla circuit may be compromised resulting in lower voltage than required for striking the arc.

KEN

Posted by John Walsh (Member # 168) on 05-01-2005, 08:30 AM:

James, how was the heat filter incorrectly installed? I've never heard of bulbs being damaged this way. For example, the heat glass in a Century JJ (4Kw bulbs) I ran was mounted at a right angle, straight to the path of light. I never had a problem with heat reflecting back.

Posted by James S. Mellen (Member # 2139) on 05-01-2005, 09:09 AM:

The split glasses were installed so that they were flat instead of angled. As I understand it, they have a dichroic coating so that they reflect IR and pass other frequencies. If they are flat, the IR bounces back to the anode of the bulb causing it to overheat. In our case, the anode connection of the bulb melted.

Posted by Kevin Orman (Member # 3076) on 05-01-2005, 01:05 PM:

I must say I've never heard of this before either, but I'm not an engineer..
More likely to be poor lamphouse cooling or loose anode connection. A colleague suffered repeated 'early' lamp failures until he discovered the lamps were being left 'loose' in the fitting when they were fitted!

Posted by Tim Reed (Member # 137) on 05-01-2005, 01:35 PM:

quote: Kenneth Wuepper
Opening the spark gap lowers the frequency and therefore makes the filtering components less effective.

Good call, Kenneth! While this is absolutely correct in theory, I have not noticed any differences in practical operation -- not with the small degree of discrepancy I am talking about. My experience has been, if it oscillates, it works. You set the gap close to what a new one looks like and you're in business. It doesn't have to be hand-wringingly precise, it's a fairly low-tech application.

Besides, the gap isn't usually specified, anyway. So the manufacturers aren't worried about it.

Posted by Frank Dubrois (Member # 3042) on 05-01-2005, 05:01 PM:

Is there a certain amount of time specific bulbs should be lasting? No matter what wattage we use 2k 3k 4k 4.5k etc, we get about 1800-2500hours (max). I heard somewhere that the 2k bulbs should be lasting close to 5000 hours?? True?

Posted by Richard May (Member # 2627) on 05-01-2005, 05:43 PM:

In all the theaters that I service that use 2K bulbs, they average between 2000-3000 hours. It depends a lot on ventilation, amperage and other factors. A lot has to do with ventilation. We use 1K bulbs and easily get 5000-7000 hours on them. We keep the the lamps on all day and have great ventilation. We also start the amperage low and increase it as the bulb ages.

Posted by Phil Hill (Member # 371) on 05-01-2005, 05:55 PM:

quote: Tim Reed
As long as it's firing, that's all that matters.

That's basically true. The spark gap distance determines the amount of power/voltage of the lamp ignition and has very little to do with operating frequency...that's determined by the LC resonate circuit.

As was mentioned, an igniter is basically a Tesla coil - a LC device with distributed-inductance and fixed capacitance acting more like a RF transmission line than a tank circuit. It is most efficient when the coil winding length is tuned to the resonate frequency peak and not at a node.

In many BIG Tesla coils, they use a synchronous rotary spark gap operating (sparking) just in time to excite the coil and then recharge the cap of the tuned circuit.

Bottom line: if it's sparking... it's working assuming no other problem elsewhere.

Posted by Glen Rich (Member # 1150) on 05-02-2005, 04:13 AM:

We are using Ushio xenons. 2.5kw in cine 2 which averages 6100hrs each lamp, and 3.6kw in cine 1 which averages 1900hrs,(I do the change of lamps when they either start to pulse or dim.) We do have a ridiculously powerful exhaust fan in cine 2 which keeps the lamphouse fairly cool to the touch.
The manufacturer recommends changing out lamps at their warranted life plus 25%, which for the 2.5kw lamp would be 1500hrs, 1250hrs for the 3.6kw.