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colourtemperature-change through electronic ballast ???????


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#1 Sebastian Matthias

Sebastian Matthias
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Posted 26 August 2007 - 10:30 AM

Hello all togethether !
Yesterday something really strange happened to me and I just can´t find an answer..........
I was checking HMI lamps for a shoot and measuring colour temperature with a colour meter
(minolta colormeter 2 ).
All lamps where fine (ranges between 5600-6000), just one lamp permanently showed values of
20000!!!!( no poop: twentythousand ) kelvin.
First I thought it might be the meter, but it measured all other lamps, the sky and everything I could think of just fine. I started changing bulbs and even lamp housings (could have been a bad lens/could have been huge amounts of UV-light coming through), but the result was allways the same.
Finally I changed the electronic ballast unit (it was a kobold) and suddenly light temperature was okay.
So my question ( an also the question of the rental house,some gaffers,,cameramen I asked for help...........):
Can a malfunctioning electronic ballast device change the colourtemperature of a HMI in such a massive way and how does this work?????????

I can´t sleep before I find an answer to this tricky question ! Noone I talked to ever experienced something like that !

Cheers

Sebastian
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#2 Richard Andrewski

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Posted 27 August 2007 - 06:35 PM

Well, I've never heard of this or seen it, but here's something to think about. When you dim an HMI or fluorescent, it definitely changes color temperature. It's also not good for the bulbs by the way. But as far as 20K color temp I would have to assume that if that really happened and the ballast was the culprit that it was overdriving the bulb past its normal voltages somehow. But I would never have expected it possible to be that much out of its normal range though. Very weird.
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#3 John Sprung

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Posted 27 August 2007 - 07:26 PM

Can a malfunctioning electronic ballast device change the colourtemperature of a HMI in such a massive way and how does this work?????????

IIRC, they go blue if they don't get enough current. Could be windings shorting out in the ballast. Did the ballast run hot? Did you get as much light as you should, or was it dimmer?



-- J.S.
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#4 Sebastian Matthias

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Posted 30 August 2007 - 07:09 AM

IIRC, they go blue if they don't get enough current. Could be windings shorting out in the ballast. Did the ballast run hot? Did you get as much light as you should, or was it dimmer?
-- J.S.


Hello John !
The ballast seemed to have normal temperature, and it was brandnew.The light output seemed to be much more and brighter
than the other lamps. That would actually have been a very good idea to measure it with a normal lightmeter !

The ballast got send back to the manufacturer, maybe they will say something to it !

I also startet a threat on this topic in CML and got some interesting answers allready.

All the best


Sebastian Matthias
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