Film-Tech Forum ARCHIVE: Xenon Bulb Question

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Posted by Mark J. Marshall (Member # 1409) on 02-26-2003, 02:24 PM:

Someone I know recently had a bulb explode on them well under warranty. The inner components of the bulb (I forget which is which off the top of my head) were discolored. The little pointy one was black, and the big round one was like a pea soup greenish color. Any insites into what could have caused the discoloration? It's an Osram XBO HOFR bulb.

Thanks!

Posted by Darryl Spicer (Member # 711) on 02-26-2003, 02:31 PM:

Well, it is a combination of things. A leak in the seal prior to explosion could have caused it. A power supply running to high could have caused it and the explosion. The bulb it's self could of had an internal defect that caused the anode and cathode to blacken do to the increase in current running across the bulb. There may be other possabilities.

Posted by Randy Stankey (Member # 64) on 02-26-2003, 04:22 PM:

Those electrodes, when heated, will discolor when exposed to air. It's possible that they turned color when the lamp exploded and the air rushed in and surrounded the red hot metal.

What would indicate a problem with the lamp's operation more than the color of the metal would be the overall condition of the metal. Does it look like some of the metal has been vaporized away? Are there pits or rough spots or even deformation of the metal?

Here! Check out THIS electrode!

This electrode is from a xenon that was in the projector for over 6500 hours. They were wondering why the picture was dim on that projector!
[Roll Eyes]

Posted by Tim Reed (Member # 137) on 02-26-2003, 07:40 PM:

Randy's right. The discoloration/coloration occurs when xenon leaks out and oxygen leaks in. Then, it burns like a big candle... consuming oxygen and creating a flame (where previously it was plasma). If the pieces of the envelope are a deep, dark-blue color, it was probably a seal leak that caused the failure.

RANDY! You're holding that in yer bare hand??!!? Don't you know those things are radioactive?!
[Big Grin]

Posted by Sam Hunter (Member # 1119) on 02-26-2003, 07:42 PM:

It will be ok as long as he doesn't use that hand to scratch his B(*&^. [Big Grin]

Posted by Randy Stankey (Member # 64) on 02-26-2003, 11:00 PM:

OH SHIT!! I carried that thing around in my pocket for a couple of days afterward! [Eek!]

How did the lamp explode?
I have seen several of them fail catastrophically but I have only ever seen one actually explode... KA-fucking-BOOM!!!
If you've ever heard a 12-guage shotgun go off right next to your head, that's what it sounds like. Glass and metal schrapnel go all over the inside of the lamphouse. It's a pain in the ass to clean up!

If that happened to you, then you witnessed a rare event, AFAIC. More often, they just go out with a fizzle and maybe a fizzle-pop. Spectacular in their own right, but nothing like a full-on explosion.

One good reason for an explosion would be fingerprints on the glass. This is a big No-No. You're just beggin' for it if you don't clean your lamps with 90% (or better) alcohol before you light 'em up. ESPECIALLY if you may have touched it with your bare hands. The oil and dirt from your hands literally boil on the surface of the glass and cause a weak spot which will eventually melt through. Yup! You guessed it... KA-fucking-BOOM!!!

Another reason would be inadequate cooling. If the metal ends of the lamp, where it clamps into the lamphouse have a bluish color to them you have a good indication of poor cooling.

If the electrodes are melted similar to the picture above then the lamp has seen some abuse... extreme hours, over current or even reverse installation. That's probably not your cause because installing a bulb backwards will kill a bulb, literally, in moments.

So, what does the aftermath look like? Got any pictures?

Posted by Rick Long (Member # 213) on 02-26-2003, 11:39 PM:

I recently had a couple of Osram's sent back for warranty due to seal failure. First time in quite a while.

Posted by Mike Rendall (Member # 1499) on 02-27-2003, 02:49 AM:

The electrodes are radioactive? I have never heard of this. Why are they radioactive, I thought the metal was some form of thoriated tungsten, why would this be radioactive? Surely if it is radioactive wouldn't they put some form of warning about it on the box

Posted by John Anastasio (Member # 607) on 02-27-2003, 04:55 AM:

Thorium is a radioactive element. In fact, there's more radioactive energy on this planet wrapped up in Thorium (named for the Norse god Thor) than in Uranium. Thorium 232 is used in the medical field and is packed with power, but not the type used in short arc lamps. It's been used for decades in the cathodes of vacuum tubes. Conveniently, it has a melting point almost as high as tungsten, so it can take the heat inside a Xenon bulb. It not only helps the electrodes to be more conductive, but when it's heated it gives off a bright white light. There's no more radiation being given off from the Thorium in your bulb, though, than from an old TV set.

Posted by John Pytlak (Member # 331) on 02-27-2003, 08:35 AM:

Radioactive thorium was also used in gas lantern mantles:

http://www.arpansa.gov.au/is_lantern.htm

http://minerals.usgs.gov/minerals/pubs/commodity/thorium/690499.pdf

Posted by Bill Enos (Member # 440) on 02-27-2003, 09:01 AM:

According to an early 70s General Electric specialty bulb catalog these are not explosions but "non-passive failures".

Posted by Gordon McLeod (Member # 33) on 02-27-2003, 09:29 AM:

It is often reffered to as catastrophic failure

Posted by John Pytlak (Member # 331) on 02-27-2003, 09:30 AM:

Which often produces "collateral damage".

Always follow xenon lamp safety procedures. Or that exploding lamp may be the last thing you ever see! [Eek!]

Posted by Bill Langfield (Member # 818) on 02-27-2003, 09:59 AM:

Clean ya damned finger nails too. [Smile]

The teeth are fine, bet your dentist loves you. (Or hates you!)

Radio activity and EXPLOSIONS! So thats why they made us buy a full on welders outfit.

BILL!

Posted by Mike Rendall (Member # 1499) on 02-27-2003, 10:45 AM:

I thought the quantities of thoria used in the electrodes was so small that radioactivity was not an issue. I use a thoriated tungsten filament in my X-Ray gun and have had to change them routinely and never knew of any radiation problems. Normally thoria is added to tungsten to improve its mechanical and electrical properties, i.e to give off prevent creep over time and to increase the electron emission (useful for spectroscopists). The normal ratio is 2% thoria. I am suprised if anything that no warnings are given to users about radioactivity, especially as we live in a sue-all world at the moment (i.e. if you can be blamed you will).

Posted by Randy Stankey (Member # 64) on 02-27-2003, 03:01 PM:

So... do you use this X-Ray gun often? You keep it in your back pocket or something?

Can you tell what color underwear people are wearing?
Can it see through lead?

Just kidding! [Big Grin]

But seriously, what do you use it for?

Posted by Mark J. Marshall (Member # 1409) on 02-27-2003, 03:24 PM:

Thanks for the info, guys. (And the physics radioactivity lesson!) [Smile]

Posted by Ray Bernardi (Member # 1615) on 02-27-2003, 04:03 PM:

I've had several bulbs fail, but I've never had a "non-passive failure". The last time I had a bulb fail was right after it was rotated and focused. I assume I damaged the seal in some way when I did it and air got to it. I always wear a face shield when I'm working on these bulbs, and I never work them hot. You're asking for it if you do that.

Posted by Mike Rendall (Member # 1499) on 02-27-2003, 05:13 PM:

Sorry, I didn't make it clear earlier, Cinema Projection is my part-time (one night a week) job. My day job is a scientist working at developing fuel cells for a large American car company. I keep my X-ray specs in my back pocket for those all important underwear viewing tasks [Big Grin]

Mike

Posted by Randy Stankey (Member # 64) on 02-27-2003, 05:18 PM:

So, sort of like the way they use X-Ray cameras to check to see that the welds in pipelines are sound, etc?

Pretty cool! [Cool]

Posted by Jack Johnston (Member # 887) on 02-28-2003, 04:51 PM:

Xenon bulbs do not explode...they express themselves dynamically!

Posted by Randy Stankey (Member # 64) on 02-28-2003, 09:38 PM:

Ever watch the TV show, "Beakman's World"?

Explosion: When something gets REALLY big, REALLY fast! [Big Grin]

Posted by Chris Wootten (Member # 283) on 03-01-2003, 06:31 AM:

I really dont think you should worry too much about the worry of radioactivity...rather the worry of the effects of the explosion after the failure. I always impress on my trainess that you should take all care with Xenons, and to treat them like they would a hand grenade, with the ring pulled. Helps em to realise the danger I think.

Posted by Mike Rendall (Member # 1499) on 03-02-2003, 01:49 PM:

I have never had a lamp blow on me, but after I smash them up before disposing of them next time I will take the electrodes to the lab and measure the radioactivity ! Will post the result, but it may be some time!

Posted by Randy Stankey (Member # 64) on 03-03-2003, 09:11 AM:

Let's just imagine that I know a place where there are about 50 or 60 of those electrodes sitting on a shelf in a cardboard box. When lamps are taken out and the glass is broken (safely) the electrodes are fished out and kept in a box, hopefully, to save them for recycling or reclaimation.

Are THAT many of them, all in one place, getting to be a hazard?

What about recycling? I KNOW that the local scrap metal dealers don't know what to do with them. I couldn't convince them that they were anything but hard steel. They would only offer me 50 cents per pound! I KNOW they are worth more than that simply based on their tungsten content.

Anybody know of a place that would buy/take them?

Posted by Aaron Mehocic (Member # 15) on 03-03-2003, 11:21 AM:

I recycle the copper trigger wires. Those are about the easiest thing to remove and the junkyards know what they are. I usually wait until I have a few pounds and copper is up. Talk about other staff members busting your balls and calling you stereotypical slurs.

Posted by Bill Langfield (Member # 818) on 03-03-2003, 12:28 PM:

OH the days of copper droppings from the carbon arc rods.
(2000ft reels, adjusting the arc every 5mins, heating up food, lighting cigarettes.. Those were the days.)

Even though it would takes months to get a few pounds, of copper,
the scrap yard would pay a hell of lot more than I thought they would.

Can't remember the figures (that was like 78-81) but I liked taking those buckets to the scrap yard.

It think it was like $120 of copper in tin that normally holds 10 kilos of Choc-Top Ice cream.

Aaron, TRIGGER wires? You'd need hundreds of them???????

At 1500$ a bulb, your in for a long wait to get a pound (or 2 Kilos) and about a million dollars of used bulbs to get 10 bucks!

Bill.

Posted by Aaron Mehocic (Member # 15) on 03-05-2003, 11:55 AM:

Bill,
Sure it takes a while to get enough to make it worth selling the copper but I'm patient. I don't buy the bulbs, my company does, so for me anything I make off the copper is pure profit. I change roughly 10 bulbs per year, plus any other precious metals I find laying around the theater, and it doesn't take to long in building up a supply to sell. Moreover, I have the space to store this stuff and it is not a sloppy mess back at the house. I'm doing my "part" to help out the environment. [Razz]

Posted by David Graham Rose (Member # 1450) on 03-05-2003, 01:47 PM:

Just to clarify a point. The Thorium doping used in the electrodes of Xenon lamp is there to increase the work function of the electrode i.e. to make it easier for electrons to leave the cathode hence requiring less energy to bridge and maintain the arc gap.

Posted by Mike Rendall (Member # 1499) on 03-06-2003, 02:56 AM:

Isn't it to decrease the work function? The work function is the amount of energy required to remove an electron from the Fermi level to the Vacuum level, increasing it makes it harder to remove an electron. (sorry to be pedantic)

Bill, regarding your bucket of precious metals, I have a tub of platinum left over from experiments, I wonder how much that would fetch (if only it was mine to sell!) I am hoping that someone will just ask me to get rid of it [Big Grin]

Posted by David Graham Rose (Member # 1450) on 03-06-2003, 10:21 AM:

Yes. Quite correct. Decrease not increase.

Posted by John Pytlak (Member # 331) on 03-11-2003, 10:58 AM:

Tungsten scrap metal:

http://www.metalworld.com/a/0167.html

http://euro.recycle.net/a/0180.html

http://asia.recycle.net/a/0180.html

http://www.metalprices.com/

http://www.buffalotungsten.com/index.html