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HMI truth or myth


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#1 Santiago Benet

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Posted 18 April 2009 - 05:56 PM

This is a long discussion between electricians in my town. When turning on a HMI electronic ballast should the dimer position should be set on max or min? I have noticed that when you turn it on low the lamp goes all the way up then sets to the dim down position. So in my opinion, it is better to leave the dimer up all the time and dim it down if you need to. I have a very good electrician colleague who says that the different manufacturer specify that the lamp should always be turned on the dim down position. If you have any facts and opinions we would love to hear them. Thanks!
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#2 Matthew Parnell

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Posted 18 April 2009 - 08:17 PM

I have always been taught to set to max when striking, makes sense to me because it puts the globe under less stress. Also electronic ballasts with electronic dimming control, like the newer powergems automatically set to full on strike. Also, some smaller lamps ie 200w that I have used wont strike at all at mins. Based on the whole concept of discharge lighting I would say set to max then strike is the way to go.

Just my two cents.
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#3 Rob van Gelder

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Posted 19 April 2009 - 08:24 AM

According to the Arri engineers who taught me at their maintenance workshop, they see it as first priority to get the bulb on the right working temperature in the shortest possible time. This is to extend the life of the bulb.
In general they advice to turn the dimmer position to MAX.
Depending on the wattage there might be different electronics at work. For instance, the 6Kw will first start up at approx. half power and then after a few minutes it will switch to full power. Then you will also notice the different color temperature that is related to the power..... dimming introduces often a higher and greener color temperature.

This is one more reason to be sensible with the dimmer function: it does alter the color of the light!

At our rental company we always test the lamps before they go out. One day, a technician told us at the maintance that the dimmer function of the 18Kw did not work. It turns out that he did not switch on the light long enough, because after some 4-5 minutes, the ballast suddenly switches into a higher power level, after which the dimmer is working.

Low wattage lamps usually start at maximum from the beginning.

Rob van Gelder,
Bangkok, Thailand
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#4 Santiago Benet

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Posted 19 April 2009 - 08:35 PM

Thanks ! for the info. I would love to hear more.
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#5 J. Lamar King

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Posted 01 May 2009 - 12:48 AM

The problems you have when not striking at MAX are 1) Sometimes the globe never reaches temp and is very blue until you turn it to MAX and 2) The Gaffer might have you walking the lamp in or swapping the lens/spotting because he assumes it's MAX but it's dimmed or saying "That doesn't look right!" :angry:
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#6 Ralph Keyser

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Posted 01 May 2009 - 12:51 PM

You always want to strike an HMI with the dimmer at Max. The folks here have done a good job of laying out why.
It doesn't seem like there should be any discussion, but I'd be interested in hearing the argument for doing it the other way. Let us know Santiago.
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#7 Jim Keller

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Posted 01 May 2009 - 06:51 PM

You always want to strike an HMI with the dimmer at Max. The folks here have done a good job of laying out why.
It doesn't seem like there should be any discussion, but I'd be interested in hearing the argument for doing it the other way. Let us know Santiago.


Well, if it's true that starting up the lamp in the MIN position shortens its life, I can think of at least one reason why a manufacturer would recommend doing it that way... :)
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