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Dimming HMI's


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#1 Stephen Price

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Posted 10 February 2010 - 06:57 AM

Hello,

For a music video I need to fade up and down several lights quickly with control. I have one 2.5kW HMI and two 1.2kW HMI lights.

I need to fade each one up and down quickly and individually form each other. Is this possible? I presume I need some sort of dimming unit, what would i need and how does it work in conjunction with the HMI's ballasts?

Many thanks

Steve
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#2 James Brown

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Posted 10 February 2010 - 07:08 AM

Hello,

For a music video I need to fade up and down several lights quickly with control. I have one 2.5kW HMI and two 1.2kW HMI lights.

I need to fade each one up and down quickly and individually form each other. Is this possible? I presume I need some sort of dimming unit, what would i need and how does it work in conjunction with the HMI's ballasts?


Hi,

Do you have to use HMI's? for the Colour?

You can't really dim HMI's - they only drop about 20 percent with the dimmer in the ballast and you defianlty cannot put them into any type of dimming device because of the ballast.

Use some larger Tungsten Units - 5k's / 10k's. If you dont have a Genny get a bunch of Blondies.

Regards, James
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#3 Stephen Price

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Posted 10 February 2010 - 07:43 AM

Thanks for your reply,

Colour shift is not an issue. I chose HMI for their punchy light source. To get the most out as possible. But I did fear that HMI's are hard to dim.

Thanks

Steve
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#4 Adrian Sierkowski

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Posted 10 February 2010 - 09:34 AM

use some PAR lights. They're super punchy, and you can dim them etc.
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#5 timHealy

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Posted 10 February 2010 - 09:39 AM

But I did fear that HMI's are hard to dim.


hard to dim? aside from the short range dimmer on square wave ballasts they are impossible to dim. They run on an arc. if you need dimming use tungsten.
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#6 Guy Holt

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Posted 10 February 2010 - 01:53 PM

For a music video I need to fade up and down several lights quickly with control. I have one 2.5kW HMI and two 1.2kW HMI lights.


If you are not recording sound but playing it back for the video, you can use "mechanical dimmers." Large rental houses should have mechanical shutters that will slide into the barndoor ears. If not you can use a piece of sheet metal that is large enough to cover the face of light at about a foot away. Set it up on a c-stand (without the arm) so that it is perpendicular to the light (acting as a blade), now to dim the light, simply rotate the sheet metal by rotating the top riser of the stand until it completely covers the face of the light. That close to the light the sheet metal will not throw a noticeable shadow when perpendicular to the light. If you are doing fairly quick fades up and down, no one will notice that the light doesn't actually dim, but blacks out from the center to the sides instead. You should spray paint the sheet metal with high heat black paint so that the polished metal doesn't bounce light. Incidentally, how had you planned to power the 2.5 HMI.

- Guy Holt, Gaffer, ScreenLight & Grip, Boston

Edited by Guy Holt, 10 February 2010 - 01:55 PM.

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#7 Ryan Thomas

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Posted 10 February 2010 - 01:56 PM

It sounds like going tungsten would be the easiest way to do this one...

I have to ask though, when you dim HMI's from the ballast, do they give you a color shift similar to dimming tungsten units?

Edited by Ryan Thomas, 10 February 2010 - 01:57 PM.

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#8 James Brown

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Posted 11 February 2010 - 05:37 AM

It sounds like going tungsten would be the easiest way to do this one...

I have to ask though, when you dim HMI's from the ballast, do they give you a color shift similar to dimming tungsten units?


Hi,

Tungsten is definitely the way to go. Saying that you will need much larger sources to match your HMI grunt of a 2.5 Par therfore needing bigger power requirements.

If you need something spotty you could use a bunch of Par cans or Source 4's and for something larger i would be using 2k, 5K or 10K Molebeams.

http://extranet.mole...?...900&id=1906

These are amazing lights and Dimmable. Still - Your 5K molebeams are still not as punchy as 2.5K par.

As discussed HMI's don't dim all that much whether they are Pars or not. When dimmed they go slightly Cooler (ie: higher colour temp) where tungsten sources are the opposite.

Cheers, James.
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