# "Tis an ex-spot bulb"



## Eboy87 (Aug 13, 2004)

I just got finished working our theater for a company that rented it out or a play. I was in charge of lighting and spots. We use Altman Voyagers at our thater. Anyway, I showed up at a rehersal at the right time 6:00 PM. the company was unprofesional and usually started 2 1/2 hours late. When I got there, I powered up the spots and cheked iris sizes, and all was fine. Just a little backround info, for a couple years, one spot was much dimmer, and purpler that the other, and we could never fix it. Well, now it is fixed. As the TD & I had an argument over who was responsable for a light board system crash (it was his fault, he started pressing buttons that he didn't know what they did), I was told to check in on the spot guys. A few minutes after being up there, I hear a loud noise and see the most fantastic fireworks display from our #2 spot. There is nothing like a 600 watt halogen bulb exploding. We got the bulb replaced, but cleaning up the glass shards was something else. Besides that, the kid using that spot was from the company that rented the place. He was scared S%$#*less about using the spot anymore. It had been one of those nights when everything went wrong. I was just glad no one got hurt.

Keep that in mind if you see a dim purple lamp with no gel.


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## ship (Aug 13, 2004)

It’s very rare that a lamp will explode no matter the hours in life the lamp has been used. Normally it’s a question of cooling, voltage and other fixture problems much less in the case of a follow spot, turning it off before the fan cooled it sufficiently given the fan was working, or turning it on too soon in a restrike condition. It’s a multi-vapor Metal Halide lamp by the way at about $180.00 each and when they blow up, they really blow up. The purple light by the way is often adjustable but frequently in difference between an old and a new lamp in their color temperature. This is given it was not a question of the lenses or dichroics within the fixture in being “green” on the one that is other in purple. Purple would designate a very high color temperature which is normal for a spot - granted purple would be unusual.

If the fixture cannot be adjusted for output in balancing the two lamps in them than it is well within your rights to request either new or a balancing of the lamps in color temperature. Most rental companies however when prepping the gear for the rental will actually do something besides turn on the lamp. They will look at both at the same time and adjust to balance or change them out so they match.


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## ship (Aug 13, 2004)

It’s very rare that a lamp will explode no matter the hours in life the lamp has been used. Normally it’s a question of cooling, voltage and other fixture problems much less in the case of a follow spot, turning it off before the fan cooled it sufficiently given the fan was working, or turning it on too soon in a restrike condition. It’s a multi-vapor Metal Halide lamp by the way at about $180.00 each and when they blow up, they really blow up. The purple light by the way is often adjustable but frequently in difference between an old and a new lamp in their color temperature. This is given it was not a question of the lenses or dichroics within the fixture in being “green” on the one that is other in purple. Purple would designate a very high color temperature which is normal for a spot - granted purple would be unusual.

If the fixture cannot be adjusted for output in balancing the two lamps in them than it is well within your rights to request either new or a balancing of the lamps in color temperature. Most rental companies however when prepping the gear for the rental will actually do something besides turn on the lamp. They will look at both at the same time and adjust to balance or change them out so they match.


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## ricc0luke (Aug 13, 2004)

Hmm.... Anyone been touching the bulbs lately? Thats the only thing I can think of.


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## ricc0luke (Aug 13, 2004)

As I thought about this... Ship brings up a very good point about shuting off cooling fans before a bulb can cool. This is not normaly a problem for theatres that run their spot lights seperate then their lighting system. However, recently at the theatre I work in we have been incorperating into the lighting system. This way the operator does not have to worry about turning the light on and off... all they have to do is point and change colors if needed. We use old spot lights.... I don't remember the name.... but they are old. In their case the cooling fan and blub are on the same switch, so shut of the light and you shut off the fan. Because this is the way they have run for years putting them on the lighting system does not concern me at all. However, the spot at our high school is different. There you need to let the fan run after the blub is shut off.
Although we have yet to put that spot on the system, if and when we do I need to run the fan from a seperate power supply than the lighting system so that it can remain on don't I?

That could take some work..... but because of the high schools set up that is not likly to happen in the next 3-4 years until they renovate the theatre.... if that ever really happens....


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## cambo1000 (Aug 14, 2004)

oops forgot to login...sorry, above post was me.


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## DMXtools (Aug 14, 2004)

Two switches? - Yes, in many cases.

Two power cords? No!

That makes it difficult to put the lamp on a relay from the light board without putting the fan on it too. Some of the better new followspots have DMX control of the lamp built-in (along with iris and color), but we're talking about older units.

John


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## Eboy87 (Aug 14, 2004)

No one has touched the bulb since I've been there, of course, it hasn't been replaced since the theater was built 7 yrs. ago I'm told. The only other thing that might have done it was this one kid who decided to play bongos on the spot during one performance. And we do keep the fans running on them for at least 10 minutes after the bulb is turned out.


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## Mayhem (Aug 14, 2004)

Eboy87 said:


> The only other thing that might have done it was this one kid who decided to play bongos on the spot during one performance.



Not sure how sensitive metal halide lamps are to shock, but from my experience, lamps generally do not like too much rough stuff. Popped a virtually new 650W lamp in a Fresnel once, because the slide stuck and I forced it a little too much. The jolt caused by the sudden stop was enough to take it out.

Now this is a question more than a suggested possible cause - could the vibration cause the lamp to become incorrectly seated? If so, could this then account for what you have reported. As it has not been mentioned as a possible cause - probably not. However, just some curiosity and lack of knowledge on my part.

Anyhow - my advice is to play bongos on the kid's head. And when has asks you to stop because his head was not designed for percussion, you can point out to him/her that neither was the follow spot!


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## Eboy87 (Aug 14, 2004)

Already did that Mayham. The problem was, he ran home to his mommy, and I got in trouble. The good thing is, he's not working the theater again.


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## ricc0luke (Aug 14, 2004)

Most spot light do have 2 switchs.... like the one at our high school.... however.... the old old old ones at the community theatre do not. Though they are really old they still do work fine so they are ok by me.

As far as touching the bulbs.... bulbs explode within about an hour or 2 use after being touch.... so if that was the reason... it would have to have been the kid, but as others have said there are several possible excuses.

Mayham- what type of fresnel are you using and with what lamp? I use altman 6" with a tungston-halagon lamp (500w). though i am not sure of the exact lamp. I have yet to see one of those bulbs burn out, and we tend to put them through a lot. Once, we even tried to se if we could fry a bulb and we couldn't. We haven't had to replace a bulb in the 1.5 years that we have had them that I know of. On the other hand... we loose at least 1 or 2 lekos at least every other show.


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## avkid (Aug 14, 2004)

fireworks are fun,but broken glass is not


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## Mayhem (Aug 14, 2004)

Hi ricc0luke,

The lamps that I have in stock for my 6" Fresnels are Thorn A1247 650W 240V (GY9.5 base). I was given several when a club closed down and have continued to use them.

I don't have to replace them very often, in fact, other than the time that one 'blew' as described earlier - I cannot recall the last time I had to change one. Keep in mind however, that I don't use them every week.

Come to think about it. When this lamp 'blew' there was no discouluration. What had happened was that the filiments had fallen appart. I am not sure how to explain it but it looks like several springs and it actually looks like you could pat it all back together again. There are no broken parts - just disassembled.


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## Les (Aug 15, 2004)

I highly doubt that the Bongo kid touched the lamp. The Voyagers' have two ways of getting to the lamp: the trap door at the back of the spotlight for lamp replacement (where you can only have contact with the reflector of the lamp) and the door on the side which is used for lens cleaning, etc... Usually touching the lamp is not the first thing that goes through your mind when you see a spotlight, much less how to get to the lamp. And I would not blame the poor kid for this incident. Even if it was his fault, he was probably not properly trained on the instrument. And no normal human being would ever reach their hand inside a machine that they are not familiar with. (especially one that incorporates high voltage, high temp, and moving parts. Maybe you should check your ballast and find out if your building has been experiencing any unusual power surges lately.


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## ship (Aug 16, 2004)

I once wanted to do a starlight effect on the cheap so I fitted a 360Q lamp base cap with 1,000w FEL lamp to a tin can with a bunch of pin hole punctures in it sealing the lamp base. Actually worked somewhat for a while but that lamp, the can and the lamp base definitely did overheat. Also due to the size of the filament, the pin-prick holes showed more like lightning lines thru them than points of light.

This being said, yes it is possible to overheat a lamp and it often depends upon the filament if not even manufacturer of lamp as to how shock resistant it is.
On touching, it all depends. Things like how much actual oil and other things were on the skin that burn off cleanly, burn off leaving a charring, or don’t burn off at all. For instance, should your Leko lamp be submitted to a good amount of oil based fog, it could be much more damaging than some dust, than again the oil from the fog would be a little more covering of the entire bulb in retaining heat all around it. 
This more important relates to how much heat will be absorbed by the contaminate in holding more heat or even as possible passing more of it given a certain amount of etching of the quartz glass. Internal pressures of gas and temperatures the lamp burns at, much the speed the pressure built up at will than have a large effect on a lamp either exploding or the internal gasses within the lamp in acting like wind doing things like bubbling the glass or deforming the filament plane. This will even be the case with a metal halide lamp given a double envelope of glass over the arc source since the outer globe will be tremendously cooler on say a 250w arc source than a single globe 5,000 Watt halogen source for instance. 

There are many ways a lamp can explode, I even have some examples of filaments shooting out of the globe as if a bullet passed thru them with glass holding the shape of the filament passing thru it. On the opposing side of the bulb from where the filament and gas shot out of the lamp, the bulb had puckered due to the atmosphere leaving the lamp. Most frequently by “finger bleeping” a lamp, you will find things like the lamp having white finger prints on it, a dark spot or nothing seen. Most frequently the effects on the lamp will be the filament pushed away from that finger print if the filament was parallel to the finger print. This pushing away from the fingerprint will stretch the filament out and even cause it to touch the glass even bubble and melt thru the glass to the point that the filament will at times still operate for a while even though it’s encased in a filament sized bubble of glass. Extra heat retention can also have dire effects on the pinch seal which is the point the lead in wires to the lamp pass thru the glass in going to the base. If this area gets too hot it’s moly foil wires can melt, the glass can pinch, the extra pressure can force it’s way thru etc. in making the lamp fail. This point of the gasses escaping the lamp where the filament still works for a moment will often be seen by pretty colors the lamp changes such as deep purples and silvers as the metal and gasses in the lamp vaporize. The glass frequently at this point will also bubble up and out in direct proportion to the hotest part of the lamp it’s filament as it goes super nova in no longer having sufficient pressure or being exposed to oxygen. This is an explosion in the lamp, but normally the glass is sufficient to retain it. If the glass were touched and oil is making that part of the bulb hottest, it’s possible this area might explode outward given it’s already very hot in retaining heat. The extra heat and pressure on the weaker part of the glass or any scratches in the bulb could cause it to explode from that point.

Lamps otherwise exploding will more frequently come from over-voltaging to a large degree, shock on an already weak filament or infrequently at the end of the lamp filament life when the filament wears away to the extent it breaks but there is sufficient amperage and proximity, plus heat in the lamp to make the incandescent lamp into a mini arc lamp for the briefest of moments while the voltage jumps the gap between the broken parts of the filament. This causes a huge flash of light and lots of heat and pressure. Given a above finger fucked part of the lamp, or other weak spots this could cause explosions.

On the Ushio website, there was once a very good pamphlet from their Dr.Bulb about the end of lamps which went into more clear details about these things. Given all of this, there is lots of ways a lamp can explode much less touching a lamp will only be a factor in it but probably not the direct cause. It’s also very rare to happen. I agree it probably was not the kid’s fault.

BTL lamps are standard 6" Fresnel types, Mayham is both using something at 240v and at 650w my guess would be something in a studio Fresnel line of fixture not a stage fixture. The BTL lamp has a very heavy duty filament which is very shock resistant by design. The largest shock problem with it often would be the lamp cracking at the point it enters it’s porcelain base at the pinch seal when hot and the glass is most fragile. When cool, this lamp is a very strong lamp type, it’s also at 120v under a lot less due to dimming, and 2,000 hours normal life at full voltage, is a very long life lamp. Much longer than the getting to be standard 115v lamp rated at 300 hours. Get the point on why it lasts longer? The Leko lamp also dependant upon lamp will also have a much more fragile filament in being a more compact size necessary because of optics but at least the same wattage.


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