HMI Light Throw

[James Daggy]

Hi,

 

Can anyone shed some light on this. logic has already answered this for me but i just want to see if anyone else has a different opinion on it before i spend money on testing.

 

Will a bank of 2x 1200 watt HMI's give near the same Output and Throw as a 2.5k HMI.

 

If this is also the case can this formula be applied exponentially?

 

Many thanks! James

[James Daggy]

Anyone with experience to this simple or not so simple answer please?

[Phil Rhodes]

Errr... probably, all other things being equal?

[Adrian Sierkowski]

Depends on which 1.2K and which 2.5K you're comparing. The manufacturer will have photometrics available, or at least should. The issue is then the double shadows you'd get from 2 sources, and if you're putting it through any diffusion the type of diffusion you're using will effect the output and throw.

[David Mullen ASC]

That's my response too -- "probably".

[Oliver Hadlow Martin]

One benefit which was not mentioned is if the lights are being used on location through a 13a mains plug (uk) the start up draw would be less if switched on one after each other. Rather than one big start up draw. I believe thats true anyway, maybe someone else knows differently.

 

Oh wait if you are in the us I think it's 1800w max per breaker (15a?) anyway so that kinda makes that pointless anyway.

[Adrian Sierkowski]

You're right about start up draw, generally; though a 1800 HMI would pop a 15A breaker pretty quick because HMIs aren't the same as tungsten, e.g. it draws more amps than it's watts would suggest. . It would probably be safe on a 20A breaker, depending on it's power factor. (and normally I tend to use paper amps when dealing with house-hold power to give myself a bit of a threshold, so 1500w on a 15A breaker, though it can really take 1800W )

[James Daggy]

Thanks for all the replies,

 

Reason why i ask is because i have started to expiriement with digital ballasts and metal halide bulbs.

 

Going second hand on some of the pro powerful units is out of my budget. The only problem I have had so far in testing is the CRI of the bulb I've used which is a standard grow bulb at 6000K

 

I have however found a suitable and expensive e40 bulb with a CRI of 93. The type used in a stadium. I can also get these in 2000watts but only using a a magnet ballast unfortunately.

 

My thoughts were if i could combine a bank of 1K. would it have the same effect as larger lights. I'm looking to get four of them as I figure a 4K light is good one to aim for. Also Why I would like to do this is that the lights could be split up when needed and could be easily managed power wise;)

 

I'll have to test if the bulbs can stand the heat of each other next to each other, How they manage when strike after each other,

 

I'm guess the light being diffused would even the light out?

Thanks again!

[Phil Rhodes]

Yes, you can do this sort of thing.

 

Some problems of which you should be aware are that most metal halide ballasts (or more properly the combination of ballast and starter, if it's a magnetic ballast) will require a cooldown period after the lamp has been on before it can be restarted. Obviously, this can be a real pain. This can be overcome by using a "hot start" ignitor, but these can only be used with magnetic ballasts as far as I've been able to tell. Magnetic ballasts will cause flicker unless you carefully manage frame rate and shutter angle. Electronic ballasts run at high frequency and avoid this problem, although they tend to have built-in ignitors and thus can't be hot started.

 

The only hot start, high frequency ballasts I'm aware of are the ones sold for the movie industry, although my information is six months old. Yes, they are expensive.

 

Also, what are you going to run your 4K metal halide cluster from?

[JD Hartman]

Wait a minute....I think we're on to something here. The goal isn't, can I get the punch and reach of a 2.5k HMI by using two 1.2's without a genny, distribution, tie-in (no, we never do tie-in's anymore), it's can I combine them to make a rig like this: http://www.visualproducts.com/storeProductDetail02.asp?productID=1074&Cat=3&Cat2=49

Imagine.... buring through brick walls, setting cast members aflame (no, not really), etc. Operating a Ruby 7 makes me feel like I'm Goldfinger in a James Bond film.

Edited October 2, 2013 by JD Hartman

[Phil Rhodes]

If I was going to do that, I'd use the little 35W metal halide lights that are built to do retrofits on car headlights, and end up with something that would look like a mini dino made out of MR16s. You can get them for US$25 apiece. They're flicker free (to the best of my ability to test with an FS700), and they hot restrike, and they're available in a variety of colour temperatures.

 

I have no idea what the colour rendering is like, and of course they are only 35W each!

 

PS move to the UK and you can run a 2.5KW HMI by plugging it into the wall. Muahaha. Well, we have to have something over you guys.

[Adrian Sierkowski]

Well we gotta concede something to our former overlords, Phil.

 

That's an interesting idea on the MR16s.

[Guy Holt]

My thoughts were if i could combine a bank of 1K. would it have the same effect as larger lights. I'm looking to get four of them as I figure a 4K light is good one to aim for. Also Why I would like to do this is that the lights could be split up when needed and could be easily managed power wise;)

 

 

Rather than re-inventing the wheel, you may want to look into ways of powering 4k HMIs off of standard wall receptacles. You can pick up a used 4k HMI Fresnel with electronic or magnetic ballast for very little money and power it off a 240V wall receptacle. There are a number 240V outlets in a typical house, office, or industrial plant in this country. The most common are air conditioner outlets, dryer outlets, range outlets, outlets for large copy machines in offices, and the outlets for motorized equipment in industrial plants.

 

If you look at the breaker of these circuits on the building service panel you will notice that they use two pole breakers - either 30A or 50A.. Each pole of the breaker is in a sense an independent 30A or 50A 120V circuit. That is, if you measure the voltage from each pole of the breaker to ground it will be 120 volts, and if you measure the voltage between the two poles of the breaker you will notice that it is 240 volts. The 120 volts of the two poles adds up to 240V because the 120V circuits are on opposing legs (and are therefore additive) of either a single-phase electrical service of a house, or a single-phase secondary step down transformer of a office or industrial plant. In residential settings, this is how higher voltages are supplied to household appliances like Dryers, Electric Ranges, Air Conditioners, Motors, etc. that require more power than can be reasonably supplied by a single 120V circuit.

 

Many of these household and industrial 240V receptacles use a three wire system (no neutral) because they are designed to power single phase motors or heating elements that draw a perfectly balanced load and return no current because the single phase service legs are 180 degrees out of phase and cancel each other out. How you use a 240V circuit to power a 4k HMI depends on whether the ballast is electronic or magnetic.

 

So that they can be used in both North America and Europe, electronic 4k ballasts are designed to operate at voltages between 95-150V and 195-250V. A power factor corrected electronic ballasts operating at 240 Volts of, say, a dryer plug will draw roughly 18.4 Amps on each leg of the single phase circuit, which is well within the capacity of these circuits which are usually rated at 20, 30, or 50 Amps per leg.

 

To operate a 120V 4k magnetic ballast from a 240V circuit requires a 240v-to-120v step down transformer like the 60A Full Power Transformer/Distro we make for the Honda EU6500is generators. Like it does with the 240V output of the Honda EU6500is Generator, our 60A Transformer/Distro can convert the 240 volts supplied by these industrial and household receptacles back to 120 volts in a single circuit that is the sum of the two single-phase legs of 30/50 amps each. That is how our 60A Transformer/Distro makes a 60A/120v circuit out of a “30A/240v” or a “50A/240v” circuit and is capable of powering bigger lights, like 4ks with magnetic ballasts, 5ks, or even a 6000W Six Light Mole Par, off a 6500W generator. It can also be used to power multiple 120V luminaries off of 240 Volt circuits because our Transformer/Distro automatically splits the load of whatever you plug into it evenly over the two legs of the 240V circuit so there is no neutral return.

 

You can maximize the power you can pull from these 240 Volt receptacles if, rather then plugging an electronic ballast directly into the 240 receptacle, you plug it in through a step-down transformer and operate it at 120 Volts. Where a 4k power factor corrected 4k electronic ballast at 120V draws only 36 amps, you will still be able to power additional lights, like a 1200 Watt HMI (11 Amps) and a 800 Watt HMI (8 Amps), of the same circuit.

 

For more detailed information on using 4k HMIs on standard wall outlets, I would suggest you read a white paper I wrote on the use of portable generators in motion picture production that will be available soon as an e-book from the Academy of Production Technology Press (APT.)( http://store.aptxl.com/ProductDetails.asp?ProductCode=BK-PGMPP)

 

 

Harry Box, author of The Set Lighting Technician’s Handbook has cited my article in the just released 4th Edition of Harry Box's “Set Lighting Technician's Handbook” (http://www.screenlightandgrip.com/html/BoxBook.html) and featured on the companion website “Box Book Extras." (http://www.screenlightandgrip.com/html/BoxBookExtras.html) Of the article Harry Box exclaims:

 

“Great work!... this is the kind of thing I think very few technician's ever get to see, and as a result many people have absolutely no idea why things stop working.”

 

“Following the prescriptions contained in this article enables the operation of bigger lights, or more smaller lights, on portable generators than has ever been possible before."

 

The original white paper is still available online for free at

 

http://www.screenlightandgrip.com/html/emailnewsletter_generators.html.

 

Guy Holt, Gaffer, ScreenLight & Grip, Lightng & Grip Rental in Boston