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HMIs: What features to look for when buying


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#1 Isabelle Landers

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Posted 22 April 2010 - 07:37 PM

I want to buy a HMI, but don't know what to look for. I can only afford to spend about $2000.00 ($3000.00 max), but don't want to buy a Chinese knock off. There are a number of used lights on ebay, but I am not certain which would be best for me. I shoot mostly indie shorts, so it is important that I be able to plug it into the wall or run it off a portable generator. From what I have seen on ebay, it seems like the most powerful light that I can afford is a 1200W. But, I am uncertain if I should get a fresnel or par light, with a magnetic or electronic ballast. I have listed a number of the options below.

Arri Par Plus w/ Electronic ballast (out of my price range unless the seller comes off their asking price)

http://cgi.ebay.com/...T#ht_500wt_1182

Desisti 1200 Fresnel w/ mag ballast

http://cgi.ebay.com/...T#ht_500wt_1182

LTM 1200 Par w/mag ballast

http://cgi.ebay.com/...T#ht_500wt_1182

Arri 1200 Fresnel w/Mag ballast

http://cgi.ebay.com/...T#ht_760wt_1167

Strand 1200 Par w/ mag ballast

http://cgi.ebay.com/...atchlink:top:en

I would appreciate any input on these lights and guidance in general.

Thanks, Isabelle Landers, Gaffer
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#2 Saul Rodgar

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Posted 23 April 2010 - 12:52 AM

It really depends on your preference. Arri and LTM are both good brands. Desisti and Strand I have never used. With Par lights you need the lenses, which can break and add to the pile of stuff to lug around. Magnetic ballasts are heavier than electronic, and tend to be more prone to flickering, depending on type and age, but tougher than electronic. Broad generalizations, I know.

I would suggest not buying one unless you are willing and can afford to do maintenance on it regularly. I own some lights, none HMI, hearing horror stories from people who own them is enough for me. I rather rent. That said, if you must buy, I recommend hanging out at grip and electric rental facilities and getting to know different lights, their pros and cons. I certainly would not rush into it. I am sure someone else here can give you additional or better advice, but I would think long and hard before buying one of these babies.

Edited by Saul Rodgar, 23 April 2010 - 12:55 AM.

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#3 Matthew Parnell

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Posted 23 April 2010 - 08:07 AM

As far as heads go it's down to personal preference and what is the right fit for you. I'm a massive fan of ARRI Par heads, and the newer 'Daylite' series from Mole Richardson.

Probably the first thing I would do if buying would be to call up a lamp/equipment repair company and have a chat to one of there technicians about what gear is going through there.

HMIs are pretty maintenance heavy pieces of gear. Savings upon purchase can very quickly be eaten up 5 years down the track on repairs.
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#4 Guy Holt

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Posted 23 April 2010 - 02:52 PM

Magnetic ballasts are heavier than electronic, and tend to be more prone to flickering, depending on type and age, but tougher than electronic. Broad generalizations, I know.


Buying a used 1200W HMI light has got to one of the hardest lights to buy. Because of the constant improvement in HMI technology there are many options available. If you are not careful you can get stuck with a lemon so I will go into more details on ballasts. In ballast design you have a choice between magnetic and electronic ballasts; and to complicate matters even more, you have a choice between Power Factor Corrected electronic ballasts and non-Power Factor Corrected electronic ballasts.

Given the type of filming you do, you may in fact be better served by an older magnetic ballast over a non-Power Factor Corrected electronic ballast. A 1.2kw non-PFC electronic ballast draws 18-19 amps ( verses the 13.5 amps of a magnetic ballast) so it will always trip the common 15 amp house circuit and will trip a 20 Amp circuit if there is something else, like a computer or light, on the same circuit. Where you can't always know what else is on the same circuit, or even if it is a 20 or 15 Amp circuit, a 1.2kw magnetic ballast drawing only 13.5 Amps is the safer bet since it can operate on a 15 amp circuit even with other things on the circuit. Non-Power Factor Corrected electronic ballasts are meant to be used on film sets where every circuit is 20 Amps and you know what is on the circuit because you are distributing the power yourself from a tie in or generator. Since your style of shooting requires that you plug into wall outlets, you will be better served by a magnetic ballast.

But that is not the only benefit to using a magnetic ballast over a non-PFC electronic ballasts. If you don’t have access to the newest PFC electronic ballasts, the older magnetic ballasts are in fact cleaner running on portable gas generators than non-PFC electronic ballasts. As mentioned above the harmonic distortion created by non-PFC ballasts reacting poorly with the distorted power waveform of conventional AVR generators limited the number of HMIs you could power on a portable generator. The primary factors limiting the use of HMIs on portable generators has been the inefficient use of power by non-PFC electronic ballasts and the harmonic noise they throw back into the power stream. The adverse effects of this harmonic noise, can take the form of overheating and failing equipment, efficiency losses, circuit breaker trips, excessive current on the neutral wire, and instability of the generator’s voltage and frequency. For these reasons it has never been possible to operate more than a couple of 1200W HMIs on a conventional 6500W portable gas generator. The increasing use of personal computers, hard drives, and microprocessor-controlled recording equipment in production has created an unprecedented demand for clean, reliable power on set.

However, now that inverter generators, like the Honda EU6500is, do not require crystal governors to run at precisely 60Hz, magnetic ballasts offer a cost effective alternative to dirty non-PFC electronic ballasts because you can operate magnetic HMI ballasts “flicker free” on inverter generators. And as mentioned above, the smaller magnetic ballasts (575-2500W) offer the distinct advantage of being less expensive and draw less power (once they have come up to speed) than the commonly available non-PFC electronic equivalents (13.5A versus 19A for a 1.2kw.)

Of course there are downsides to using magnetic ballasts. One down side is that you are restricted to using only the safe frame rates and shutter angles. But, when you consider that every film made up to the early 1990s were made with magnetic HMI ballasts you can see that being limited to the safe frame rates is not all that restrictive. Another downside to magnetic ballasts is that you can’t load the generator to full capacity because you must leave “head room” for their higher front end striking load. When choosing HMIs to run off portable generators, bear in mind that magnetic ballasts draw more current during the striking phase and then they “settle down” and require less power to maintain the HMI Arc. By contrast, an electronic ballasts “ramps up”. That is, its’ current draw gradually builds until it “tops off.”

While older HMIs with magnetic ballasts are less expensive to purchase or rent, Power Factor Correction (PFC) makes the newest electronic ballasts worth the extra money when it comes to lighting with portable generators. The substantial reduction in line noise that results from using power factor corrected ballasts on the nearly pure power waveform of an inverter generator creates a new math when it comes to calculating the load you can put on a generator. In the past we had to de-rate portable gas generators because of the inherent short comings of conventional generators with AVR and Frequency governing systems when dealing with non-PFC electronic ballasts. The harmonic distortion created by non-PFC ballasts reacting poorly with the distorted power waveform of conventional AVR generators limited the number of HMIs you could power on a portable generator to 75% of their rated capacity (4200Watts on a 6500W Generator). But now, where inverter generators have virtually no inherent harmonic distortion or sub-transient impedance and power factor correction (PFC) is available in small HMI ballasts, this conventional wisdom regarding portable gas generators no longer holds true. Where before you could not operate more than a couple 1200W HMIs with non-PFC electronic ballasts on a conventional generator because of the consequent harmonic distortion, now according to the new math of low line noise, you can load an inverter generator to capacity. And if the generator is one of our modified Honda EU6500is inverter generators, you will be able to run a continuous load of up to 7500W as long as your HMI and Kino ballasts are Power Factor Corrected.

Power Factor Correction (PFC) is very new in 1200W HMIs and so it is highly unlikely you will find it in a used ballast – even a Power Gems or Arri ballast. Since Power Factor Correction (PFC) is not mandated in this country, as it is in Europe for any electrical device that draws more than 75W, we are pretty much ignorant of Power Factor and effect that poor Power Factor can have on a distribution system. However, any film technician familiar with large HMI heads will be quite familiar with Power Factor and Power Factor Correction (PFC.) That is because after a false start back in the 90s, all major manufacturers now include PFC circuitry in HMI ballasts in the 6-18kw range. They do so by necessity. The early line of Lightmaker electronic ballasts were nick named by film electricians “Troublemaker” ballasts because they were not Power Factor Corrected and proved that PFC circuitry was absolutely necessary in large ballasts to reduce heat and returns on the neutral, and to increase ballast reliability (beware, some are still kicking around ebay). But, because of the added cost, weight, and complexity of PFC circuitry, ballast manufacturers in the US still only offer PFC circuitry as an option in medium-sized 2.5-4kw ballasts. And, until very recently manufacturers did not offer PFC circuitry in HMI ballasts smaller than 2.5kw in the US (in the EU PFC circuitry in mandatory in all HMI ballasts sold.)

Part of the reason was that PFC circuitry did not offer a huge advantage when plugging into house power. A typical 1200W Power Factor Corrected electronic HMI ballast will draw 11 Amps at 120 Volts verses the 19 Amp draw of a non-PFC electronic ballast. While not a huge advantage when plugging into house power, the added efficiency of a PFC 1200 ballast can make a huge difference when powering a lighting package off of a portable generator. For example, when you consider that a Kino Flo Parabeam 400 draws only 2 amps, the 8 Amp difference between using a PFC 1200W electronic ballast and standard non-PFC 1200W electronic ballast, can mean the difference between running four additional Parabeam 400s on a portable generator or not – I think you would have to agree that is a major boost in production capability and pertinent to any one using a portable generator as their principle source of set power.

Except for one notable exception, when manufacturers do offer PFC circuitry in smaller ballasts it is at a premium, adding as much as a $1000 to the cost of a 1200W ballast for instance. But where PFC is still very new to smaller heads, it is still the case that almost every 575 - 1200 W electronic ballast that you will find in a rental house or for sale used in North America will be a non-PFC electronic ballast. For a detailed explanation of PFC see my post "What is Power Factor Correction in HMIs" at http://www.cinematog...showtopic=43872

I would suggest you read the article I wrote for our company newsletter (especially the section titled “New Life to Old Ballasts”) on the use of portable generators in motion picture lighting. In it I cover some of the basic electrical engineering principles behind poor Power Factor, the harmonic distortion it can generate, and how it can adversely affect generators. The article is available at http://www.screenlig...generators.html.

As far as used HMIs that are available for sale I would caution you against buying a system with Lightmaker ballast. As mentioned above Lightmaker ballasts were the first generation of non-PFC electronic ballasts made and were nicknamed the “Troublemaker” ballasts because of the problems they caused. While the Power Gem & Arri ballasts are of a later generation, the used ones out there will likely be also non-Power Factor Corrected. Which is why you may be better served by a magnetic ballast for your type of filming.

Guy Holt, Gaffer, ScreenLight & Grip , Boston
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#5 Saul Rodgar

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Posted 23 April 2010 - 05:40 PM

Guy, you're the man. Good job on that thorough explanation.
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#6 Isabelle Landers

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Posted 29 April 2010 - 07:37 PM

As far as used HMIs that are available for sale I would caution you against buying a system with Lightmaker ballast. As mentioned above Lightmaker ballasts were the first generation of non-PFC electronic ballasts made and were nicknamed the “Troublemaker” ballasts because of the problems they caused. While the Power Gem & Arri ballasts are of a later generation, the used ones out there will likely be also non-Power Factor Corrected. Which is why you may be better served by a magnetic ballast for your type of filming.


Thanks everyone for you helpful suggestions. I think I will take Guy's advice and hold out for a 1200W Par with a compact magnetic ballast.

Isabelle Landers, Gaffer, Nashua, NH
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#7 timHealy

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Posted 12 May 2010 - 10:13 PM

I can confirm from experience that Lightmaker ballasts were the absolute worst.

The grief they caused were not worth it. If I had a job with them I tried to get magnetic backups for all. Today electronic ballasts are extremely reliable save a few minor quirks. It is not necessary to get magnetic backups unless you are doing something special or maybe you are shooting a few states away from the support of your rental house.
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#8 Guy Holt

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Posted 14 May 2010 - 12:48 PM

I can confirm from experience that Lightmaker ballasts were the absolute worst. The grief they caused were not worth it. If I had a job with them I tried to get magnetic backups for all.


What kind of problems did you have with the Lightmaker ballasts? Sharing your grief will lessen the pain and perhaps save someone from wasting a lot of money on the number of used HMI systems being sold with Lightmaker ballasts.

Guy Holt, Gaffer, ScreenLight & Grip, Boston
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#9 William Coss

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Posted 14 May 2010 - 03:20 PM

Isabelle,

One thing that you should also consider is the quality of the light that is put out by the fixture. How even is the field, edge to edge?
What is the fall off like on the edges? What is the focusing range from spot to flood? Can it be dimmed and be used with regular house power or automatic voltage input selection for international use?

My choice: Dedolight DLH400D

Sweet,
Bill
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#10 JD Hartman

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Posted 14 May 2010 - 04:34 PM

Unless you pickup a few "good" HMI systems at fire sale prices, will it pay to have HMIs in your inventory? If you have them for your own use and don't rent them out, how many jobs before you can consider them "paid for"? If you do rent them out, will you get similar rates to your local rental house? Then there is the damage, maintenance and general wear and tear issues....
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#11 timHealy

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Posted 16 May 2010 - 11:12 AM

What kind of problems did you have with the Lightmaker ballasts? Sharing your grief will lessen the pain and perhaps save someone from wasting a lot of money on the number of used HMI systems being sold with Lightmaker ballasts.

Guy Holt, Gaffer, ScreenLight & Grip, Boston



If I remember correctly. First time works. Then turn on second time. Didn't work. Check voltage, didn't work. Change header, didn't work. Change head, didn't work, Change ballast, didn't work. Change bulb, didn't work. Something like that.

I'm glad I haven't seen one in years.
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