HMI light?

[Kujtim Ereqi]

I never used HMI lights before and I know theoritically what they do, but I would be interested to have more information about that.
Can anybody guide me to some good websites or forums that cover professionally HMI lighting issues?

Thanks.

 

[Ketch Rossi]

If you just do a search under HMI you can find so many places to read about it that is no point to really link them here.

HMI's main issues were flickering but this is caused by the Ballast themselves and not the fixtures, also this is only the case with older Ballasts, so make sure to get Flicker FREE ballasts if and when you purchase any HMI lights, or Fluorescents for that matter!

Also I would check in to some CDM (Ceramic Discharge Metal-halide) lights, this produce the great lighting ratio as HMI's and are also Daylight, unfortunately at the moment they are just available in small wattage.

Use the following link to get some more info, and look the site there is some useful info on the HMI and other lighting as well: http://www.coollights.biz/hardlight....html?osCsid=baed4e10923b72bfb37f059612b3a1c8

 

[Ryan S]

HMIs are, as I understand it, more efficient in terms of power consumption and light output than quartz/tungsten lighting. I've only really researched Arri and Dedo fixtures, but they seems to cost about 2-4x as much (or more) as the equivalent tungsten fixture, and even a 150W HMI fresnel will have a sizable ballast.

HMIs are lovely, and great for using with the Red. But don't discount tungsten- you can still achieve great images with them, especially with the new color science on the Red One.

Ketch is absolutely correct (as he usually is!) that Googling HMI (or searching it on Reduser) will yield you a ton of information.

 

[Richard Andrewski]

Thanks Ketch for mentioning our product!

HMI is part of the "metal halide" family of lighting and similar to fluorescent in terms of power consumption when compared to tungsten which is the benchmark for a lot of measurements. The term HMI doesn't really mean anything, it's just a trademark of Osram Corporation for a particular type of metal halide bulb family with characteristics that the film / television industry were looking for: daylight (6000K), high CRI (85+), small and compact, availability in common stage bulb socket types of single or double ended, relatively long life, energy efficient and hot restart (whether the bulb is hot or not, you can restart it given a hot restart type of ballast driving it). The fixture that uses the bulb isn't really an "HMI" thus, but that's the slang that people call it now. Its technically a metal halide or HMI fixture. A Phillips 575w MSR bulb is not an "HMI" either, but people still call it that as well--its just an HMI compatible or clone to be more technically correct.

Fluorescent and HMI both will give around a 4 to 1 efficiency against tungsten. So, a 150w HMI would be roughly equivalent to a 650w tungsten. A 575 HMI would be roughly equivalent of a 2500w tungsten, etc. Where the similarity to fluorescent ends is in terms of throw and type of light. HMI is a very "hard" light because its a small point source from a single bulb. A fluorescent is a very "soft" and diffused light because it comes from a much larger bulb. Thus the hard light will give a longer and stronger throw given a good fixture to put it in than a fluorescent will.

Also in the metal halide family and mostly used for commercial and architectural lighting is "CDM" or ceramic discharge metalhalide. Cool Lights, my company adapted some of these to use in film/t.v. type fixtures and they've been accepted well. The main difference between CDM and Osram's HMI and compatibles is the hot restart feature is missing. This means you have to wait for the bulb to cool down for about 5 minutes before you relight. Not a problem for many indy type productions. If it is a problem, you simply use regular HMI which we also carry at Cool Lights.

Someone mentioned ballast size on the 150w being very large. Our 150w CDM ballast is about 8.5 x 3.5 x 1.5 inches. Weighs less than a pound. I don't think that's very big at all and our CDM 70w is even smaller than that.

 

[Pietro Impagliazzo]

Wiki is a good start: http://en.wikipedia.org/wiki/Hydrargyrum_medium-arc_iodide

This is a great book on lighting:

http://www.amazon.com/gp/product/02...&pf_rd_t=101&pf_rd_p=470938131&pf_rd_i=507846

 

[Tom.Wong]

HMI lighting also shows up on Red a lot better then tungsten. Generally speaking, daylight always shows up stronger in all mediums, from film to digital. They fixed a lot of it in the new build for Red, but it's been a known issue that tungsten tends to look grainer on a Red, and of course you can color correct all day to give it a tungsten look but you'll probably never get the same feel as if you just lit it with tungsten. but you end up using more tungsten to get the light you need so there's are the pros and cons. HMI's tend to be harder to control because it is so powerful, so best to practice your craft.

 

[Eileen Ryan]

HMI Lights?

HMI Lights?

Can anybody guide me to some good websites or forums that cover professionally HMI lighting issues?

A gaffer/rental house owner/operator I work with in Boston, Guy Holt at ScreenLight & Grip (SL&G), has just compiled for his company’s news letter what is probably the best information regarding HMIs that I have seen anywhere. In his article, he undertakes a comprehensive survey of the prevalent lighting and portable power generation equipment, describes how he systematically tested how well they work together, and has made the results available online.

To paraphrase what he found, harmonic distortion of set power by HMI electronic ballasts is an increasing problem in HD production. It is becoming an issue because portable generators were not designed for the abundance of non-linear loads, like the electronic HMI and Fluorescent lighting, that make up lighting packages today. The problem is being further compounded by the increasing prevalence on set of sophisticated electronic production equipment like computers, hard drives and HD monitors which require clean power, but are themselves sources of harmonic distortion.

Normally, when you plug an HMI light into a wall outlet you need not be concerned about the current harmonics generated by HMI ballasts producing voltage distortions. The impedance of the electrical path from the power plant is so low, the distortion of the original voltage waveform so small (1-3%), and the plant capacity so large, that inherently noisy loads like HMI ballasts placed upon it will not affect the voltage at the load bus.

However, it is an all together different situation when plugging HMIs into conventional portable generators. Given the large sub-transient impedance of conventional portable generators, even a small degree of harmonic noise being fed back into the power stream will result in a large amount of distortion in its’ voltage. Add to that, the likely hood that the percentage of the generator’s capacity taken up by electronic HMI & Kino ballasts will to be very high given its small size relative to typical lighting packages, and given the increasing prevalence of these types of light sources in production. Finally, add that the original supply voltage waveform of a conventional generator is appreciably distorted to begin with, and you have a situation where the return of any harmonic currents by an HMI ballast will result in significant waveform distortion of the voltage at the power bus.

The power waveform below left is from his article and is typical of what results from the operation of a couple of 1200W HMIs with non-power factor corrected ballasts on a conventional portable generator. The adverse effects of the harmonic noise exhibited here, can take the form of overheating and failing equipment, circuit breaker trips, excessive current on the neutral wire, and instability of the generator’s voltage and frequency. It is for these reasons, he argues, that it has never been possible to reliably operate more than a couple of 1200W HMIs with electronic ballasts on a conventional 6500W portable gas generator. Harmonic noise of this magnitude can also damage HD digital cinema production equipment, create ground loops, and possibly create radio frequency (RF) interference.

In the past, attention was given to generator features such as automatic voltage regulation and crystal speed regulation. But, given the rise in production problems associated with harmonic noise, an increasingly more important feature today is the quality of the generated power waveform and how well it interacts with the lighting units predominantly used today. For that reason, he did a series of tests that he summarizes in the article.

His tests have resulted in some rather startling conclusions. They show that when your lighting package consists predominantly of non-linear light sources, like HMI and Fluorescent lights, it is essential to have PFC circuitry in the ballasts and to operate them on an inverter generator. The combination of improved power factor and the nearly pure power waveform of the inverter generator creates clean stable set power (like that in the power waveform above right) that is capable of reliably operating larger lights (HMIs up to 6kw or Quartz lights up to 5kw), or more smaller lights, off of portable gas generators than has ever been possible before. For example, as I mentioned in a previous post, I used one of their modified Honda EU6500is Generators on a Red shoot to power a 7500W lighting package that consisted of a 2.5kw, 1200, & 800 HMI Pars, a couple of Kino Flo ParaBeam 400s, a couple of ParaBeam 200s, and a Flat Head 80. Given the light sensitivity of the Red Camera, this was all the light we needed to light a large night exterior.

The second startling result of the tests was that If you don’t have access to the newest PFC electronic ballasts, you are better served by using the older magnetic ballasts on an inverter generator like the Honda EU 6500is over non-PFC electronic ballasts (more on this in my nest post below.)

I highly recommend that anyone using HMIs on a set read his article. While the HMI lighting package he has developed as a result of his tests is new (introduced Jan 09), the set power issues caused by HMI ballasts have been vexing electricians for years. The article explains the electrical engineering principles behind these issues, and how his lighting package resolves them, in a way I have not seen elsewhere. In fact his tests will be cited in the upcoming 4th edition of the “Set Lighting Technician’s Handbook.” The article is posted on ScreenLight & Grip’s website at:
http://www.screenlightandgrip.com/html/emailnewsletter_generators.html

Eileen Ryan, Gaffer, Boston

 

[Eileen Ryan]

HMI Lights?

HMI Lights?

HMI's main issues were flickering but this is caused by the Ballast themselves and not the fixtures, also this is only the case with older Ballasts, so make sure to get Flicker FREE ballasts if and when you purchase any HMI lights, or Fluorescents for that matter!

Ketch is correct, but only when it comes to powering HMIs off of grid power. As discussed above, it is an all together different situation when plugging non-PFC electronic HMI ballasts into conventional portable generators. The return of harmonic currents generated by non-PFC electronic HMI ballasts results in significant waveform distortion of the voltage at the power bus. If you don’t have access to the newest PFC electronic ballasts, you are better served by using the older magnetic ballasts on an inverter generator like the Honda EU6500is over non-PFC electronic ballasts. I know this is contrary to the conventional wisdom, but it is true non the less.

When electronic square wave HMI ballasts came on the market, they were at first thought to be the solution to all the problems inherent in running HMI lights on small portable generators. By eliminating the flicker problem associated with magnetic ballasts, they also eliminated the need for the expensive and ultimately unreliable AC governors required for flicker free filming with magnetic HMI ballasts and portable gas generators. Since they are not frequency dependent, it was thought at first that electronic square wave ballasts would operate HMI more reliably on small portable generators – even those without frequency governors.

For this reason, as soon as electronic square wave ballasts appeared on the market, many lighting rental houses replaced the more expensive crystal governed portable generators with less expensive non-synchronous portable generators. The theory was that an electronic square wave ballast would operate reliably on a non governed generator and allow filming at any frame rate, where as a magnetic HMI ballast operating on an unreliably AC governed generator allowed filming only at permitted frame rates.

In practice, electronic square wave ballasts turned out to be a mixed blessing. Part of the problem with operating electronic HMI ballasts on portable gas generators in the past has to do with the purity of the power waveform they generate. With an applied voltage waveform distortion of upwards of 19.5%, conventional generators do not interact well with the leading power factor (current leads voltage) of the capacitive reactance created by electronic square wave HMI ballasts. The net result is harmonic currents are thrown back into the power stream, which results in a further degradation of the voltage waveform and ultimately to equipment failure or damage (for the reasons discussed in my previous post.)

The oscilloscope shots of the power waveforms below is from the article mentioned above and is typical of what results from the operation of a 1200W HMI with non-power factor corrected ballast on grid power (left), on a conventional generator (middle), and inverter generator (right.) The adverse effects of the harmonic noise generated by non-PFC electronic ballasts and exhibited here in the middle shot, can take the form of overheating and failing equipment, circuit breaker trips, excessive current on the neutral wire, and instability of the generator’s voltage and frequency. Harmonic noise of this magnitude can also damage HD digital cinema production equipment, create ground loops, and possibly create radio frequency (RF) interference.

As is evident in the oscilloscope shots below of a 1200W magnetic HMI ballasts on grid power (left), on power generated by a conventional Generator (Honda EX5500)(middle), and power generated by an inverter generator (Honda EU6500is)(right), the lagging power factor caused by the inductive reactance of magnetic ballasts has by comparison only a moderately adverse effect on the power waveform. Outside of causing a voltage spike in the inverter power, magnetic ballasts actually show a positive effect on the already distorted power waveform of the Honda EX5500 conventional generator. For this reason magnetic ballasts work better on conventional generators with frequency governors than do non-PFC electronic square wave HMI ballasts.

These oscilloscope shots show that 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. And, where inverter generators like the Honda EU6500is do not require crystal governors to run at precisely 60Hz, you can operate magnetic HMI ballasts reliably on them. In addition, 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 before the early 1990s was made this way, you realize it is not such a limitation. 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.”

For example, even though a 2.5 magnetic ballast draws approximately 26 amps you will not be able to run it reliably on the 30A/120V twist-lock receptacle of a 6500W generator’s. As mentioned above, magnetic ballasts have a high front end striking load. So, you must leave “head room” on the generator to accomodate the strike. And, even though the twist-lock receptacle is rated for 30 Amps, conventional 6500W generators are only capable of sustaining a peak load of 27.5 Amps per leg for a short period of time. Their continuous load capacity (more than 30 minutes) is 23 Amps per leg. And, if there is any line loss from a long cable run the draw of a 2.5 magnetic ballast will climb to upward of 30 Amps. To make matters worse, the lagging power factor caused by the inductive reactance of the magnetic ballast kicking harmonic currents back into the power stream causes spikes in the supply voltage that can cause erratic tripping of the breakers on the generator or ballast. (for a more detailed explanation of why that is I, again, suggest you read SL&G’s newsletter article.) In my experience the load of a 2.5kw magnetic ballast is too near the operating threshold of an unmodified 6500W generator for it to operate reliably.

The only sure way to power a 120V 2.5kw (or even a 4kw) HMI magnetic ballast on a portable gas generator is from its' 240V circuit through a 240v-to-120v step down transformer like the one SL&G manufactures for their modified Honda EU6500is. SL&G’s 60A Full Power Transformer/Distro will step down the 240V output of the generator to a single 60A 120V circuit that is capable of accommodating the high front end striking load, and even the voltage spikes, of either a 2.5kw or 4kw magnetic ballast at 120V.

For more details on how this is accomplished I suggest you read their very informative newsletter article on the use of portable generators in motion picture production which I mention above. The article is available at www.screenlightandgrip.com/html/emailnewsletter_generators.html.

Eileen Ryan, Gaffer, Boston

 

[onsighthawaii]

all that info is great and informative but rather moot in todays hmi rental market. and i think an overkill per the OPs request. no descent rental facility will be without power factor corrected hmis and inverter generators. the industry standard honda 5500 has been phased out for the newer 6500, magnetic ballasts are almost a special request, and no ballast manufacturer has made a non-pfc electronic unit in quite awhile.

 

[Eileen Ryan]

HMI Lights?

HMI Lights?

all that info is great and informative but rather moot in todays hmi rental market....no descent rental facility will be without power factor corrected hmis and inverter generators. the industry standard honda 5500 has been phased out for the newer 6500, magnetic ballasts are almost a special request, and no ballast manufacturer has made a non-pfc electronic unit in quite awhile.

I respectfully disagree with your assessment of the hmi rental market – at least the market here in North America. Where PFC circuitry in mandatory in all HMI ballasts sold in the EU, it is not in the US. While it is true that all major manufacturers include PFC circuitry by necessity in HMI ballasts in the 6-18kw range (to reduce heat, returns on the neutral, and increase reliability), in the US they offer PFC circuitry as an option on medium-sized ballasts (2.5-4kw). And, because of the added cost, weight, and complexity of PFC circuitry, manufacturers have not until very recently offered PFC circuitry in HMI ballasts smaller than 2.5kw in the US. 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. The new ballast manufacturer Power-2-Light, on the other hand, is including PFC circuitry in their ballasts at the same price point as other manufacturer’s non-PFC ballasts. But where Power-2- Light is still very new to the market, it is still the case that almost every 575 - 1200 W ballast that you will find in a rental house in North America will be a non-PFC electronic ballast.

Here in Boston (not a provincial market by any means) all the rental houses with the exception of ScreenLight & Grip have only non-PFC electronic ballasts available for heads in the 575-1200W range. As for 6500W generators, many still have primarily the non-inverter Honda ES6500 generator. In fact, a Red Camera rental house here by the name of Film Star Rentals has only a crystal governed Honda EX5500 to offer.

The information I have presented in this thread is not moot in the Boston rental market, and I would bet that is also the case just about anywhere else with maybe the exception of NY & LA. It is certainly not moot in the area of independent feature production where by cost necessity filmmakers are using HMIs with magnetic ballasts that they are either renting or buying cheaply. In the past, much attention was given to portable generator features such as automatic voltage regulation, speed regulation, and AC Frequency because magnetic ballasts were prevalent. Today, given the harmonic currents generated by the non-PFC electronic ballasts prevalent in rental houses and the problems they cause, an increasingly more important feature today in portable generators is the quality of the generated waveform. This is especially true of the systems to be used in low budget independent production because these productions are more susceptible to the adverse effects of harmonic distortion because they are also increasingly embracing the use of HD digital cinema production tools, like inexpensive HD camcorders, laptop computers and hard drives, that require cleaner and more reliable power on set to operate effectively.

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 princple source of set power.

Eileen Ryan, Gaffer, Boston

 

[Stephen Strangways]

Eileen, thank you so much for sharing your knowledge.

I would like to share the following from the Kino Flo website, for everyone's information:
http://www.kinoflo.com/FYI/FAQs.htm

In particular:
"Why is the neutral drawing more than the hot leg?

Kino Flo ballasts are generally not power factor corrected. They will draw double the current on the neutral from what is being drawn on the two hot legs. On large installations it may be necessary to double your neutral run so as not to exceed your cable capacity. The Diva-Lite and ParaBeam series of fixtures are power factor corrected and do not need additional capacity on the neutral."

And this might be of interest:
"Can I use an inverter and battery pack to operate a Kino Flo ballast?

Kino Flo recommends a pure sine wave inverter. Inexpensive saw tooth or near sine wave inverters may not work."

 

[onsighthawaii]

thats unfortunate, and hard to believe, for boston and its customers. i live in the worlds most remote market and supply the smallest of projects and all i carry are pfc units and the latest honda inverter generators. never had problems with non pfc units and older "putt putts" in the past whether shooting tape, digital, or film. it really makes no difference.
it just seemed an odd tangent, with respect to the original posters very general request for hmi information and considering the use of hmis with small non-professional generators is one small aspect of their use and really a minority situation even in "independent feature production." again interesting info.

 

[Eileen Ryan]

The Diva-Lite and ParaBeam series of fixtures are power factor corrected and do not need additional capacity on the neutral....Kino Flo recommends a pure sine wave inverter. Inexpensive saw tooth or near sine wave inverters may not work."

Even though older HMIs with magnetic ballasts and Kinos with non-PFC ballasts are less expensive to purchase or rent, its worth paying the extra money, I feel, to get the newest HMIs and Fluorescent Lighting fixtures (like the Kino Flo Parabeams) with Power Factor Corrected ballasts when your power is coming from a portable generator. The substantial reduction in line noise that results from using power factor corrected HMI & Kino 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 & Kino 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 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 ScreenLight & Grip’s 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.

According to this new math, when you add up the incremental savings in power to be gained by using only PFC HMI ballasts, add to it energy efficient sources like Kino's Parabeam fixtures, and combine it with the pure waveform of inverter generators, you can run more lights on a portable gas generator than has been possible before. For example, as I mentioned in a previous post, I used one of SL&G’s modified Honda EU6500is Generators on a Red shoot to power a 7500W lighting package that consisted of a PFC 2.5kw HMI Par, PFC 1200, & 800 HMI Pars, a couple of Kino Flo ParaBeam 400s, a couple of ParaBeam 200s, and a Flat Head 80. Given the light sensitivity of the Red Camera, this was all the light we needed to light a large night exterior. For more details on how this is accomplished I suggest you read their very informative newsletter article on the use of portable generators in motion picture production which I mention above. The article is available at www.screenlightandgrip.com/html/emailnewsletter_generators.html.

Eileen Ryan, Gaffer, Boston

 

[ericyoung]

Hi Eileen

Thanks very much for taking the time to post to what's turned out to be an interesting thread. Your very detailed technical notes are so useful. Please don't make them less technical as one response seemed to suggest.

On a tangent, I'm a TV studio electronics engineer qualified to PAT test the gear I use in studios and domestic electronics, but haven't got involved in anything to do with power or lighting as our studio electricians usually take responsibility for all that.

However, I recently picked up a secondhand Strand Quartzcolor 1.2K HMI with Power Gems EB125 hotstrike flicker free ballast, and a couple of 4ft 4bank Select Kinoflos and as I'm becoming a freelance cameraperson I'd like to be able to PAT test the lighting gear I've acquired.

Is there anything specific to HMI's or Kinoflos that I need to consider when PAT testing the lamps and the ballasts?

Also, the HMI came with two bulbs of uncertain usage/age. They may be brand new or previously used, but came only in bubblewrap. They look very new to my untrained eye. I've heard that HMI bulbs are always replaced after a certain number of hours so that they don't fail explosively but not sure if this is a myth!

I spoke to one of our own studio electricians, and he said there weren't any particular considerations for testing ballasts, and while any bulbs can shatter, it wasn't an age related thing. Ie. you could run an HMI bulb until it stopped working or had shifted colour temperature outside an acceptable range.

I'm based in the UK if that has any bearing on our types of ballasts.

I'd really appreciate your view on these questions. Thanks!
Eric

 

[Guy Bryan Holt]

HMI Light?

HMI Light?

it just seemed an odd tangent, with respect to the original posters very general request for hmi information ....

Where Eileen was addressing Ketch Rossi’s blanket assertion that you want to “make sure to get Flicker Free ballasts … when you purchase any HMI lights” I don’t find her remarks tangential at all. She was not addressing the original question, but trying to correct the popular misconception reflected in Ketch’s following remark.

HMI's main issues were flickering but this is caused by the Ballast themselves and not the fixtures, also this is only the case with older Ballasts, so make sure to get Flicker FREE ballasts if and when you purchase any HMI lights,...

There is a popular misconception that you should only use electronic ballasts with portable generators. Where that is true with conventional generators without crystal governors, as Eileen suggests in her post, it is not true of inverter generators like the Honda EU series. In the interest of full disclosure, I should say at this point that in addition to being a gaffer, I own and operate ScreenLight & Grip – the rental house Eileen mentions that rents and sells the equipment she recommends above. If what I am about to say sounds like I’m hyping certain product lines it is not because we rent and sell them. We are dealers and rental agents for just about all the major brands and I don’t stand to profit from the sale or rental of magnetic HMI ballasts since we made the transition to PFC electronic ballasts. As a professional Gaffer of a lot of tight budgeted historical documentaries for PBS’ American Experience and The History Channel (see my “credit-entials” on Imbd), I think it is worth noting that magnetic ballasts are still a viable production tool when used with the new inverter generators because they offer low budget independent filmmakers a cheaper alternative to high priced rental house equipment.

Magnetic ballasts will operate reliably on the Honda EU series generators because Honda's sine-wave inverter technology provides much higher quality power than conventional (non-inverter) generators. With a waveform distortion factor of less than 2.5%, the power generated by Honda’s EU series of generators is quite often better than what you get out of the wall outlet. The power these machines generate is rock solid with a frequency variance of only hundredths of a cycle - which eliminates the need for costly crystal governors. The Honda EU series generators provide true sine wave power with low enough distortion, and frequency stability, to power HMI's with magnetic ballasts without problems. As long as you shoot at one of the many safe frame rates, magnetic ballasts are also “flicker free” (where the topic of safe frame rates for magnetic ballasts is discussed extensively elsewhere in this forum I won’t get into it here.) Besides the extra bulk and weight of magnetic ballasts, the smaller magnetic ballasts (575-2500W) offer the distinct advantage of being less expensive and drawing less power (once they have come up to speed) than the commonly available electronic equivalents.

Another popular misconception is that a Honda 6500 can run no more than a couple of 1200 HMIs. This misconception stems from the fact that there is just enough room on the 20A circuits of the generator for either a 1200W electronic ballast or “head room” for a 1200W magnetic ballast; while, there is not enough “head room” on the 30A/120V Twist-lock receptacle to accommodate the high front end striking load of a 2500W 120V magnetic ballast. While that is true when plugging the lights into the generator’s 120v receptacles, it is not true when plugging the same lights into the generator’s 240V twist-lock receptacle through a 240V-to-120V step-down transformer.

A step down transformer gives you access to the full power of the generator in a much larger 120V circuit that is capable of powering larger lights or more smaller lights than you can power off the generator’s 120V receptacles. For example, as Eileen has mentioned, we have developed a 60A full power transformer that doubles as a distribution panel, that when used with a Honda EU6500is we modify, provides 7500 Watts in a single 120V circuit. Part of the reason our modified Honda EU6500is is capable of powering larger HMIs is that the larger circuit created by the transformer provides enough head room to accommodate not only the front end striking load of 2500W 120V magnetic ballasts, but also 4000W 120V magnetic ballasts as well. Our modified Honda EU6500is generator can power these bigger HMIs because the transformer splits the load evenly over the two legs of the 240V circuit of the generator. Split into two smaller loads that require less “head room” each, the large front end striking load of large HMIs fit easily on the generator. The same holds true of large tungsten lights like 5ks.

Our 60A Full Power Transformer/Distro also enables you to more fully utilize the continuous rated power capacity of the EU6500is by enabling you to load it more fully. Without a transformer you can never fully utilize the available power of a portable generator because the load of a light has to go on one of the 20A circuit/leg of the generator or the other. For example, when plugging lights into the power outlet panel of a Honda 6500, you reach a point where you can't power an additional 1kw light because there is not 8.4 amps available on either one of the factory installed 20A outlets/leg of the generator. With a transformer you can still add that 1kw light because the transformer splits the load evenly over the two legs (4.2A/leg) of the generator. Now that you are able to fully load the generator in a perfectly balanced fashion with the help of a transformer, you are able to not only power more smaller lights than you could without it, but also larger lights. For example our 60A Full Power Transformer/Distro is capable of powering 4kw HMIs, 6000W Molepar Six Lights, Quartz 5k, or a complete lighting pkg.

When you add up the incremental savings of using only PFC HMI ballasts, and add that to the extreme power efficiency of the latest fluorescent and LED lights, you will find you can run a lot on a portable generator with a transformer. For example, our modified Honda EU6500is Generator with our 60A Full Power Transformer/Distro is capable of powering a 2.5kw Par along with a 1200 and 800 Par, plus a couple of Parabeam 400s, a couple of Parabeam 200s, and a Kino Flo Flat Head 80. Given the light sensitivity of your 500 ASA film this is more than enough light for your night exterior shoot.

If it sounds like I’m hyping the Honda EU6500is generator, it is not because we rent and sell them. As a Gaffer of a lot of tight budgeted historical documentaries for PBS’ American Experience and the History Channel, it is my professional opinion as a gaffer that when used with step down transformers these machines are a major advance in portable power (use this link for more information about using transformers with portable gas generators: http://www.screenlightandgrip.com/html/hdfilmstrip4lg.html.)

- Guy Holt, Gaffer, Owner/Operator of ScreenLight & Grip – a lighting and grip equipment rental, sales, and production service company in Boston.

 

[Eileen Ryan]

HMI Lights?

HMI Lights?

Is there anything specific to HMI's or Kinoflos that I need to consider when PAT testing the lamps and the ballasts?

Also, the HMI came with two bulbs of uncertain usage/age. ...They look very new to my untrained eye. I've heard that HMI bulbs are always replaced after a certain number of hours so that they don't fail explosively but not sure if this is a myth!

I am not that familiar with the requirements of the PAT test in the UK. But, in my experience GFI (ground fault interrupt ) breakers do not like non-PFC HMI ballasts because the harmonic currents they return on the neutral has a tendency to induce current in the ground wire which trips GFI breakers. If the PAT test tests for ground leaks, a non-PFC ballast is likely to fail. I would be interested to know if the Power Gem 125 ballasts you get in the UK have PFC circuitry as standard equipment. The ones we get here in the states do not.

It is possible to determine the age of an HMI bulb by its color temperature. The color temperature drops one degree Kelvin for every hour it burns and the bulbs are good for about 750 hours. New their color temperatures are somewhere between 5500-6000 degrees Kelvin, so a bulb that is 4750-5250 is on its last leg. The bulbs are vacuum sealed so they will implode rather than explode (Xenon bulbs will explode.) They seldom do either. Invariably what happens is as the electrodes in the bulb degrade with age the gap between them grows so wide that the ballast can not create enough potential to maintain an arc and they just won’t hold a strike. The Power Gems 125 Ballast you have is what we call a constant power ballasts that is designed to give you consistent color temperature regardless of the age of the bulb, so you will not be able to determine the age of the bulbs by their color temperatures on the Power Gems ballast. To use color temperature as a test of age you must measure them on a magnetic ballast. Quite often rental houses keep magnetic ballasts around just for this purpose.

Eileen Ryan, Gaffer, Boston

 

[ericyoung]

All useful information Eileen. Much appreciated!

I'll try and find out about whether my UK Power Gems 125 is PFC or not, and report back.

Incidentally, what test equipment is used for PAT testing lights in the US?

 

[Guy Bryan Holt]

HMI Light?

HMI Light?

never had problems with non pfc units and older "putt putts" in the past whether shooting tape, digital, or film. it really makes no difference. …considering the use of hmis with small non-professional generators is one small aspect of their use and really a minority situation even in "independent feature production."

Harmonic distortion is a relatively new issue in electrical distribution and in generators of all sizes – not just portable gas generators like the Honda. One must appreciate that the power generation and electrical distribution systems developed for motion picture production were never designed to deal with an over abundance of non-linear loads like electronic HMI and Kino Flo ballasts. It’s a problem that has only recently begun because of the increasing use of these types of non-linear lighting loads. The problem is being further compounded by the increasing prevalence on set of sophisticated electronic production equipment like computers, hard drives and HD monitors which require clean power, yet are themselves sources of harmonic distortion.

There is no question that the magnitude of the Total Harmonic Distortion (THD) seen in the oscilloscope shots above can cause erratic behavior in other equipment running on the same distribution system as non-PFC HMI & Kino ballasts. According to the Caterpillar Application and Installation Guide for "Electric Power Applications, Engine and Generator Sizing": “Most loads will continue to operate with THD at 15 to 20%. However, loads with sensitive electronic equipment can develop problems with THD greater than 5%.” The THD value of the severe voltage waveform distortion, generated by two 1200 Pars (with non-PFC ballasts) operating on a conventional AVR gas generator, that can been seen in the oscilloscope shots in my article (available at www.screenlightandgrip.com/html/emailnewsletter_generators.html) is well over 100%. There is no question that THD values of this magnitude in a power waveform will have severe adverse effects on equipment operating on it. Effects such as overheating, circuit breaker trips, high currents on the neutral wire, and instability.

For example a local broadcast rental house sent several non-linear editing systems to the Iron Man Triathlon for filed editing. The laptops kept inexplicably locking up until their power supply was changed from a large diesel generator that was also supplying a large number of HMIs to the onboard generator of a satellite truck. Once they were moved from the highly distorted power supply of the lighting generator to the relatively pure power supply of the satellite truck the laptops operated flawlessly.

Harmonic distortion when using a generator is enough of a problem to warrant several sections in the third edition of the “Set Lighting Technician’s Handbook.” To quote Harry Box (Page 337 under “Power Problems from Electronic Loads”):

“Much of today’s lighting technology relies on electronics such as DC rectifiers (electronic HMI ballasts), silicone-controlled rectifiers (SCRs), capacitors (magnetic & electronic HMI ballasts), and high-frequency switching power supplies (the IGBTs of electronic ballasts). These kinds of load can have undesirable effects on the current waveform, revealing themselves in the form of overheating or failing equipment (skin effect), efficiency losses, circuit breaker trips (skin effect), excessive current on the neutral wire, interference and instability with generators (not a problem according to Brian), noisy or overheating transformers and service equipment, and even loosened electrical connections. In the following sections, we discuss the power factor and current harmonics and look at their effects. Your awareness of these effects will help you to build systems that avoid or mitigate problems and show how to test for problems.(the parenthesis are mine)”

Now does this sound like harmonics is simply not a problem when using a generator for lighting. As you can see in the side by side oscilloscope shots of a 1200W non-PFC electronic ballast powered by grid power, power generated by a Honda EX5500 with frequency governor, and a Honda EU6500is inverter generator from my article that Eileen posted above, because of the subtransient reactance of conventional AVR portable generators, the harmonics kicked back by a single 1200W non-PFC electronic ballast can have a severe adverse effect on the power waveform at the generator power bus.

These oscilloscope shots (available at www.screenlightandgrip.com/html/emailnewsletter_generators.html) also demonstrate that the artifacts of harmonics are amplified to a lesser degree in the inverter generated power than the non-inverter power. This is because, as previously discussed in this thread, the original waveform of the power generated by the EU6500is (a inverter generator) has a lower subtransient reactance and less harmonic distortion at the outset than that originally generated by the EX5500 (a conventional AVR generator.)

- Guy Holt, Gaffer, Owner/Operator of ScreenLight & Grip – a lighting and grip equipment rental, sales, and production service company in Boston.