Lamp bulb burst but it still works?

[Derek220]

At a place I volunteer at there's several PAR64 fixtures using 500W PAR64 lamps (hope that makes sense). Occasionally 1 lamp will burst/fail and someone needs to get a ladder out and replace the lamp. The lamp shroud cracked this past Sunday but the filament continued to operate. Honestly it may have been functioning for weeks before someone noticed it.
How common is it that a lamp would crack but the filament remains operable?
Is there something that should be done to prevent it in the future?

 

[Mac Hosehead]

Of course the lamp still works because the filament has it's own glass enclosure. This occurrence is not so uncommon with PAR lamps. To prevent, without too much trouble, replace with a nice fresnel incandesent fixture.

 

[JimmyM]

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This video goes over this briefly, remember a Par lamp is both the lamp, and the optics, the Par can merely a receptacle for holding and pointing it

 

[brucek]

That could be thermal shock. Any chance the lamp had moisture on it? Or was very cold when first powered?

 

[almorton]

I had one do that where the connectors on the back of the lamp had completely detached from the glass, and of course the capsule inside was fine, but you'd occasionally see flashes when focusing where the power connectors contacted the "silvering" inside the glass of the reflector and vapourised it. Got binned pretty quickly.

 

[Mac Hosehead]

This failure is the reason why some PAR fixtures have a metal mesh built inside. It will catch the big pieces of glass from falling out. However, small pieces of hot glass can still make it through.

 

[Derek220]

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This video goes over this briefly, remember a Par lamp is both the lamp, and the optics, the Par can merely a receptacle for holding and pointing it

Nice!
Curious, should I be calling it a lamp?

 

[Derek220]

That could be thermal shock. Any chance the lamp had moisture on it? Or was very cold when first powered?

Pretty low chance of it getting moisture on it, but not impossible. These fixtures are hanging about 16 feet above the floor in a sanctuary/worship center. A youth group meets in there about once a week and might* have gotten moisture in it. Some of the youth group attendees like to throw random things around, a flying water bottle/soda that burst isn't beyond possibility (a couple of other thought: Would bubbles put enough moisture on it? If someone brought in a haze machine would haze get enough moisture on it to cause a problem?)

In regards to the temperature thought, these fixtures are inside, and the spare lamps are stored inside. The lamps are at room temperature by the time they are installed. But with the thought of different temperatures, Would a jerry-rigged bolt touching the lamp cause an issue? These fixtures were bought used and some of the fixtures have bolts that might touch the sealed lamp.

 

[almorton]

You really don't need a steel bolt contacting the glass.

There's a saying; Bulbs grow, lamps glow.

 

[DELO72]

Making PAR lamps is 75% science, and 25% magic-- that's according to one of my coworkers who used to work as an engineer in the PAR64 line in Winchester, KY back when Sylvania was making their PAR56 and PAR64 lamps there. The Glass reflector and lens are VERY difficult to flame seal together without creating stress in the quartz, which is what happened here . When they get hot or subject to temperature shifts, the thick quartz can shatter along those stress points. It doesn't mean anything was done wrong by anyone, it's just going to happen a lot more often that it did in the past. Back in the day, GE and Sylvania used Corning glass ($) that was very low expansion, and better able to survive. [Most] modern PAR64 lamps are made in China, often using Borosilicate glass (Pyrex anyone?) or Soda Lime glass which has a slightly higher expansion coefficient. This glass is cheaper and doesn't handle expansion due to high heat as well. That's why some modern "Pyrex" ovenware explodes, and the stuff your Grandmother had lasted forever.

The reason the lamp is sealed is that it has a nitrogen (inert) gas fill, which help prevent oxygen from getting at & attacking the Moly Foil/weld in the press seal area of the lamp capsule, which in turn increases lamp life. It's the same reason some metal Halide lamps (HMI, HSD, HSR) all have outer envelopes and inner capsules. It will still work without that environment, but it will result in shorter life.

 

[almorton]

Some of the China PARs we bought when the mainstream manufacturers became scarce suffered envelope failures; that all makes sense.

 

[Jay Ashworth]

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This video goes over this briefly, remember a Par lamp is both the lamp, and the optics, the Par can merely a receptacle for holding and pointing it

Very briefly; Alec was mostly talking about sealed-beam lamps, which do *not* have a separate capsule.

Well, the traditional ones; newer halogen replacements do...