Follow spot bulb blowing??

[the-techi]

Hello There,

 

This week I am follow spotting for a show with a Pani 1202 HMI spot.

 

I was just wondering, what happen if the bulb blows? Does it smoke and everything like people say it does?

 

Cheers

 

J

[paulears]

Nope - it just goes out and you suddenly cannot see where it was. Sometimes when there are two spots, it takes a while to work out which one went out!

 

I've had the odd one where the bulb did go pop, but I've never had one explode - although I'm sure some people will have, just never happened to me. Usually I just get a "My lights gone out" on the cans, and then we do a bit of a re-jig to try and cover.

 

Certainly I wouldn't worry about it.

[Don Allen]

Providing the bulb is always changed when it reaches its recommended maximum hours, you should never come across a bulb exploding in normal service. It might happen with a brand new design, where bugs can creep in, but not a proven design.

 

The hour counter should always be reset when a new bulb is fitted so people can keep track of its hours.

[adam2]

In most cases the lamp will simply cease to light.

They can explode at end of life, especialy if run to failure rather than replaced at the recomended intervals. This can be very startling to the operator, but not dangerous since the lantern is designed to safely contain the pieces.

[Tomo]

This can be very startling to the operator, but not dangerous since the lantern is designed to safely contain the pieces.

It's still dangerous to let them run until they blow.

Because the lantern will almost always catch the bits the first time - but not necessarily the third or fourth time it happens.

 

A site that regularly lets their discharge lamps run well over rated hours may be likely not to replace a cracked IR/UV shield, reflector and other parts that get damaged when a lamp goes boom.

[Modge]

Not in a follow spot but I've heard an MSR1200 go pop, above the noise of a sound check. It is pretty loud.

[TheLightsTech]

I'm not sure how similar the HMI is to the arc lamps in movers, but those can pretty much vaporize when they go. When that happens it's generally not terrible dangerous, you just don't want to breathe it. So in otherwords if you every have a lamp go boom, avoid breathing it in. :-)

 

You'll be fine :up: ! Good luck on the show.

[gareth]

I'm not sure how similar the HMI is to the arc lamps in movers

In many moving lights, the arc lamp is an HMI. So the answer is 'very similar indeed'.

 

but those can pretty much vaporize when they go. When that happens it's generally not terrible dangerous, you just don't want to breathe it. So in otherwords if you every have a lamp go boom, avoid breathing it in. :-)

Do you actually know what you're talking about?

[PoppaDom]

Methinks not...

[TheLightsTech]

That's what a very good ME (professional) told me as far as the glass being vaporized and it not being terribly dangerous. And it's kinda common sense that breathing vaporized glass it bad... or at least could be.

[paulears]

Not really wishing to stir, but at what temperature does glass vapourise? Bearing in mind it can contain the arc in the first place. Lamps tend to implode, not explode, and the net result is simply lots of debris, which is very hot for a short period of time.

 

I've spent a while doing a bit of research looking at research on the risks of lamp failures, and practically all the information relates to the risk of contact with the glass debris from the envelope shattering. There are numerous mentions of the toxic nature of the gas, but all the information seems to suggest ventilation and non-inhalation as the only required processes that need to be invoked on a breakage.

 

Much of the research also links to the hazard now becoming more common as ordinary incandescent lamps get replaced with compact fluorescents - containing the same kind of gasses. As this is a consumer issue, if there was a problem, I'm pretty sure one of the consumer protection agencies would have banned them already.

 

I think we're seeing risk here where it doesn't really exist - based on the number of breaking lamps we are very near when they go, which in my thirty odd years is zero!

[Guest lightnix]

I think we're seeing risk here where it doesn't really exist...

Ain't that the truth

 

I think I can count on the fingers of one finger, the number of times I've seen a follow spot bulb blow in action.

 

In reality, the quality of light output will probably have become unacceptable, well in advance of the maximum hours being reached and the lamp will probably have been changed, before there is any danger - real or imaginary ;)

[Jivemaster]

In the early days of discharge lamps there was a risk of explosion if the capsules were run to their ultimate end. NPL at Teddington did lots of research and with the new capsules and the current design of the lantern housing -that has to be designed to retain all shrapnel, there is little or NO problem. The accredited life of a discharge tube always was the service time to half the original Lumen output.

[Tomo]

CFLs and HIDs are not in any way comparable, Paul.

 

CFLs don't have much of a pressure differential, and have a very low surface temperature.

 

HIDs have a very high pressure differential, and a very high surface temperature.

- Most HIDs are also double-envelope. The internal envelope contains the high-pressure gas, the external envelope

 

I've been near several MSR1200 going 'boom', seen the devastation inside the fixture and poured the resultant mess out of the Cyberlights in a previous job.

 

That said - they don't vaporise the glass. They burst into a cloud of tiny shards (majority approx. 3-5mm across) that then rattle around the inside of the fixture.

These shards are hot, and definitely travelling pretty fast.

 

The Cyberlights had cracked heatshields and chipped reflectors, which leads me to me believe that it's likely that a second or third burst may not have been fully contained.

 

So I'd say again - the first burst will almost certainly be safely contained.

But if the fixture isn't properly repaired, later bursts may not.

 

(After the third one went boom, we finally got a budget to replace the lamps on a sensible timescale. I think the compromise we came to was running them to a max. of 120% rated lifetime. I never did convince them that we should replace them all simultaneously though - apparently manpower was 'free')

 

Jivemaster is right that the rated lifetime is to half of original output, however some manufacturers also state a 'maximum recommended' runtime that's their consideration of 'it will survive this long, even if the output is terrible'