Author Topic: So how violent are metal halide lamp explosions?  (Read 321 times)
mdcastle
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So how violent are metal halide lamp explosions? « on: December 01, 2016, 08:00:43 PM » Author: mdcastle
Thought occurred to me of using my 175 watt lamp and ballast in my photography light instead of an 85 watt CFL. The cone is made of very heavy fabric, with a light fabric scrim about 18 inches from the lamp. Good idea or no?
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wattMaster
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Re: So how violent are metal halide lamp explosions? « Reply #1 on: December 01, 2016, 08:28:04 PM » Author: wattMaster
I would assume that the fabric is flame-retardant, but I wouldn't do it unless it's a quick test.
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Re: So how violent are metal halide lamp explosions? « Reply #2 on: December 02, 2016, 12:52:11 PM » Author: Zarlog
It should be fine, but just to be safe you should use a protected bulb.
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Ash
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Re: So how violent are metal halide lamp explosions? « Reply #3 on: December 02, 2016, 01:16:01 PM » Author: Ash
It may explode always, there were known cases even with Incandescents exploding and setting fire to stuff

For equipment safety : protected lamp is excellent, unprotected lamp is unprotected but if lamp is high quality and not used past its rated life/in wrong burning position, ballast is high quality, the risk is minimal

For personal safety : you have to have a way to stay safe if the thing catches fire anyway (and it does not have to be caused by the lamp at all). Tools to extinguish a small fire on hand is allways good to have

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tolivac
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Re: So how violent are metal halide lamp explosions? « Reply #4 on: December 03, 2016, 12:14:26 AM » Author: tolivac
18in should be OK-but you should check the outer scrim to make sure it isn't overheating.IE melting or getting burn spots. The only MH violent failures I have had-so far only two.The first-250W probe start MH.Got a used fixture from a electrical surplus-had a well blackened lamp in the light.Turned it on and the bulb chose that time to die.It made a muffled POP and went out-parts of the arcd tube rattled inside the outer bulb-didn't break it.Second-100W MH Philips CMH-arc tube blew and the outer bulb looked like it was shot with a .22 rifle-the bulb was intact but two holes in it where the arc tube blew.Found peices of the tube in the fixture.Didn't hear it go.The ends of the arc tube were still being held by their supports.The Philips bulb came with the light-another yard sale find.Keep looking at the sales for vacuums and lights!
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Re: So how violent are metal halide lamp explosions? « Reply #5 on: January 07, 2017, 04:41:11 PM » Author: lights*plus
Use a lamp with a UV shield.
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Medved
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Re: So how violent are metal halide lamp explosions? « Reply #6 on: January 08, 2017, 09:49:22 AM » Author: Medved
The explosions may range from nearly nothing, via just an arctube damage, to really smashing the outer and having the hot quartz pieces flying all around. The occurrence of such events is somehow correlated with the use pattern, but still even when you never let the lamp burn for longer than just few hours without cooling down, use a quality lamps and ballasts, still the violent explosion is a thing to not forget about when designing the fixture.

The problem with pretty any fabric is, although it won't sustain fire for longer than a second or so (being flame retardant just means it does not continue to burn on its own, but it does not mean it won't burn at all), the hot quartz pieces will burn holes through it and fall below without loosing any significant amount of its heat, so remain still quite potent to set fire underneath.

Dangerous are bigger chunks of the hot material (except really dusty floor, normal materials need some exposure time and energy to actually catch fire that really spreads), so about 1cm steel wire mesh should be enough to contain most of the fire danger, while still do not block the light, nor the cooling air flow.
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Re: So how violent are metal halide lamp explosions? « Reply #7 on: January 10, 2017, 04:29:20 PM » Author: Flurofan96
If it were me then I would use a shrouded MH lamp
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Re: So how violent are metal halide lamp explosions? « Reply #8 on: January 10, 2017, 05:47:09 PM » Author: lights*plus
Eons ago I was working next to a videographer covering a wedding. He had 4 halogen floods on tall stands lighting the main reception area, one of which had a funny bluer color for a lengthy period. They must've been 1000 watts tungsten halogen. As the wedding entourage was making their entrance, that bluer halogen suddenly turned a brilliant white and exploded with violence. The unit didn't have a glass cover & the center part of the halogen tube went flying like shrapnel glowing brightly red landing on the carpet behing the entourage - luckily missing everyone. The carpet quickly melted leaving a hole where the red-hot 2" piece of tube landed...but that was it as it cooled rather quickly. It's the most violent lamp failure I've seen. And I've seen a couple of M-H lamps pop. The lesson learned:  No matter what the flavor, always have bright-hot arc-tubes behind glass.
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