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HMI hot re-strike


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#1 Sing Lo

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Posted 26 January 2007 - 07:58 PM

Is it true that the hot restrike capability of a HMI light fixture depends entirely on the bulb itself?

Or it depends on both the bulb and the ignitor ( or the ballast)?

My Osram 575W HMI bulb has definitely re-strike capability according to the manufacturer's data sheet but I am not sure if my lamp head ignitor step-up transformer has the capability to rise the voltage automatically from 5kV to 25-30KV during hot restrike. It runs on a fairly modern magnetic ballast that I can't any information about its capability and specifications. I dare not to try a hot re-strike in case something unpredictable may happen..or I am just paranoid. :unsure: ..Handling EHT device always makes me nervous although the ballast has ground test button. Hope someone here can advice. thanks.
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#2 Phil Rhodes

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Posted 26 January 2007 - 08:29 PM

Hi,

Both. The ignitor needs to push a much higher voltage through the higher pressure gas in a hot lamp, and the lamp needs to put up with it.

Phil
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#3 Hal Smith

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Posted 26 January 2007 - 08:57 PM

Or it depends on both the bulb and the ignitor ( or the ballast)?

Hot restriking reduces lamp life considerably. I've done some research on this subject, talking to engineers at GE Lighting and have had conversations with technical staff at High End Lighting. Both say to avoid hot restriking if at all possible.

High End said their experience is it's best to avoid any restriking, turn the light on before you need it and leave it on until day's end. They use MSR's, a very close relative to HMI's (some would say they're exactly the same thing, just different marketing) and they say the clouding that occurs on the inside of the lamps with high hours has happened during the lamp's cool-down cycles so leaving the lamp on extends life.
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#4 Sing Lo

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Posted 27 January 2007 - 04:23 PM

Thank you very much for the answers. I would avoid hot re-striking completely. I heard that the permanent clouding of the globe is something to do with crystallisation of the quartz glass after many hours of use. One clouding is formed, the structural property of the glass may be weaken and the globe will be proned to explosion during strike.

I also read that frequent turning the lamp on and off with cold strikes would also reduce the life of the globe significantly. I guess the electrodes burn faster during ignition phase when there is large current passing through them before the choke action of the ballast kicks in.
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#5 Walter Graff

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Posted 28 January 2007 - 08:57 AM

Is it true that the hot restrike capability of a HMI light fixture depends entirely on the bulb itself?

Or it depends on both the bulb and the ignitor ( or the ballast)?


Both the ignitor and lamp are factors in how well or how fast a fixture restrikes.
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#6 Sing Lo

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Posted 28 January 2007 - 02:32 PM

thanks Walter, I have been reading your tutorials on the use of cucaloris to produce dappled background.
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#7 Kenny N Suleimanagich

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Posted 28 January 2007 - 11:09 PM

While talking to the head of MOle-Richardson, Larry Parker, he told me that theres a 2 minute window where it is safe to restrike, and after that it is necessary to wait 15-20 minutes. It all depends on power source, if you're on a genny it's going to (I've seen this happen) strain the phase you're on, and especially if your ballast is relying on 4 lengths of stingers, voltage drops and strains are a big factor.
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#8 Sing Lo

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Posted 29 January 2007 - 09:46 AM

While talking to the head of MOle-Richardson, Larry Parker, he told me that theres a 2 minute window where it is safe to restrike, and after that it is necessary to wait 15-20 minutes. It all depends on power source, if you're on a genny it's going to (I've seen this happen) strain the phase you're on, and especially if your ballast is relying on 4 lengths of stingers, voltage drops and strains are a big factor.



Cheers kenny, this 2 minutes safe window is all new to me. Here is a quote from "Set Lighting Technician's Handbook" by Harry Cox which is not quite the same advice :unsure: :


"The electronics of most newer ballasts take this into account and have better hot restrike performance; often, however, an older magnetic ballast cannot produce sufficient voltage and you have to wait the lamp has cooled (2 or 3 minutes) before you can restrike."


I will wait 15 minutes for the cooling of the globe; to be safe than sorry.
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