Film-Tech Forum ARCHIVE: What would you light with a 24 kW HMI?

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Posted by Stephen Furley (Member # 1277) on 05-16-2012, 03:08 PM:

I was looking at Youtube yesterday, and found a few videos by Mole Richardson. Most of them featured a new fixture they have produced for a 24 kW HMI. Sadly, they don't show it operating.

The biggest HMI I've actually seen working is the 12k. The biggest made was I believe the 18k until recently. Being metal halide lamps these have a much higher luminous efficacy than xenons and even 12k ones put out a heck of a lot of light.

What would you use a 24 kW one for? I'm guessing that these would bu used outdoors; it seems unlikely that even the largest indoor sets would need to be lit with anything this big. Fill light in scenes in bright sunlight possibly? At the end there's even talk of a 36 kW version being developed in the future.

Interestingly, in another of their videos a man demonstrates the operation of a carbon arc brute, and suggests 'throwing away your HMIs'. I don't think he's being too serious, and it must be about ten years since I last saw brutes being used, but Mole Richardson do still list two sizes of them in their rental lists.

Posted by Bruce Hansen (Member # 281) on 05-16-2012, 04:57 PM:

24KW HMIs are used to make the electric company happy. [Big Grin]

Well, most, if not all of them, would be run on an on set generator, so they are to make the oil companies happy. They could also be used for night lighting, producing something like moon light.

Posted by Scott Norwood (Member # 30) on 05-16-2012, 05:41 PM:

Here is the Brute arc video. He doesn't say what size the carbons are, but the actual assembly inside the lamp looks sort of like an Ashcraft lamphouse in reverse (the negative comes in at an angle from the front of the unit). He also misses some important points (positve is larger in diameter than negative, how many inches per hour of each are used, etc.).

Still, those lights are awesome, and I want one at home....

The largest light that I've ever seen in real life is a 10k tungsten, but I think that those are pretty common.

Posted by Jeff Taylor (Member # 443) on 05-16-2012, 06:10 PM:

I wonder what those carbon spotlights mounted on a trailer with a gen set the Army used for antiaircraft use in WWII were rated at. Probably fairly puny by current standards. I know there are guys who still maintain those for store openings and the like.

Posted by Randy Stankey (Member # 64) on 05-16-2012, 06:36 PM:

I wonder if the popcorn story is really true.

Y'know... Like the story of the theater projectionist who kept his lunch in the lamphouse and exploded a can of beans all over the inside of the projector in the middle of a movie.

While, yes, I'm sure that there is truth to the story, things like this have a tendency to reach urban legend status where everybody has heard about "a friend of a friend" who knows a guy who did it but nobody has actually seen it happen.

It would be funny if it really happened. Maybe this is a case for Mythbusters? [Wink]

I want a brute arc, too! [Big Grin]

Posted by Stephen Furley (Member # 1277) on 05-16-2012, 07:28 PM:

Scott,

There were projection arcs which were similar in design to this; they were condenser arcs rather than reflector ones. Some eary Philips DP70s were fitted them, but I never saw one; I think they were Peerless Hi-candescent. Some follow spots also used a similar arrangement; I've operated one where the long positive came through a hole in the back of the lamphouse, so a longer positive could be used, but you had to put the arc out for a few seconds and re-trim to burn the second half.

The negative in the Ashcroft arcs was at a shallower angle, and this was claimed to be an advantage of them, but I can't remember why. The follow spot positives didn't rotate like the Ashcroft ones do. I'm not sure if the Brute ones do.

Quite a few years ago something was being filmed at St. Pancras station in London, now the terminal for the Eurostar trains, but then served by normal trains to the East Midlands; it was a rather quiet station then. The action was taking place on a platform, and the lights were near to the barrier line. No filming was taking place, I think it may have been a lunch break or something, but I was speaking to a friendly lamp operator. I remarked that you didn't see many of those now, and he let me strike the Brute which he'd just re-carboned. They must be much more expensive to run than HMIs.

Have you seen the picture of the filming of the opera scenes in 'This is Cinerama' at Teatro alla Scala in Milan? The very large arcs which were used to light those scenes were supplied by Mole Richardson, and were specially flown out from England. They also made some projection arcs, including the ones used on the handful of Kalee Vistavision machines ever built, and the more conventional Kalee machines used for the 34 mm presentation of 'Around the World in 80 Days' in London.

I want to see one of those 24 kW HMIs running. The lamp itself is surprisingly small; it doesn't look any bigger than a 12k one. The 12k one is claimed to produce 1.3 million lm, and since large discharge lamps tend to be more efficient than smaller ones the 24k version should be able to do slightly more than twice that. I've got a 70 W metal halide lamp in front of me at the moment, and even that's pretty bright.

Posted by Jon Miller (Member # 163) on 05-16-2012, 09:30 PM:

quote: Randy Stankey
It would be funny if it really happened. Maybe this is a case for Mythbusters?

The MythBusters tried heating a sealed can of beans that as part of the exploding Lava Lamp episode. IIRC, they tried it with a pop-top can and the contents shot out of the can like a mortar.

Posted by Jim Cassedy (Member # 4115) on 05-16-2012, 10:45 PM:

quote: Bruce Hansen
24KW HMIs are used to make the electric company happy.

No Kidding! I just "did the math" on this, and based on my
personal monthly electric usage in my 4-room apartment here
in San Francisco, it would take me 8.5 years to use as many
KW/hrs of electricity as this light uses in just 1 hour! Wowza!

I looked at the "spec" & price sheets on the Mole Richardson
website, and couldn't find a replacement 24K bulb listed.
Anybody have any idea of what a new 24KW HMI bulb costs?

Posted by Scott Norwood (Member # 30) on 05-16-2012, 11:01 PM:

Jim must have an electric clock and nothing else plugged in at his apartment.

I average something between 800-1200 kW/h per month (I have electric heat, which contributes significantly to this in the winter). At my relatively insane electric rate of about $.17/kW/h, would be paying about $4.25 per hour to run this beast of an HMI, if the wiring in this apartment could even handle it (it couldn't). Actually, it would be somewhat more because the HMI power supply is not 100% efficient (and assuming that the 24kw refers to the bulb itself, not the whole assembly including power supply).

I do wonder how many gallons of diesel fuel are required to run a generator to run this type of light for an hour, though. Does anyone here know anything about generators? I know a tiny bit about the type that are commonly used for data centers (the smaller ones usually use a diesel Caterpiller tractor engine to power a generator; you generally just spec them based on generating capacity and desired runtime...higher-end models run on natural gas and have the advantage of not having to be refueled by truck; they usually don't put out great quality power, so a good UPS/power conditioner is still needed). I know little to nothing about the type of generators that are used for film production, however.

Posted by Phil Ranucci (Member # 3820) on 05-16-2012, 11:43 PM:

A 12K HMI is about $1200, so north of that. It's been a long time since I've done any location work, but a brute ballast was great for keeping you nice and toasty when up in a Condor lift. IIRC they ran on ~70 volts DC so it was possible to hook 2 in series without ballasts on a 120VDC line and strike them together using a chewing gum wrapper on one lamp as an ignitor/ jumper.Generators are diesel and I don't recall seeing them getting filled up so I think they're not too thirsty. Most were in the range of 700-1200 amps 3 phase AC or single phase DC. They are also blimped and almost inaudible within 10 feet.

Posted by Stephen Furley (Member # 1277) on 05-17-2012, 05:02 AM:

A 500 kVA generator burns 90 litres of Diesel per hour; I know that because we had one in our car park at work for several years, and it was in the specification on the website of the company we rented it from.

Allowing for ballast losses it's probably going to take about a couple of gallons per hour to run the 24 kVA HMI on an electronic ballast. It's surprisingly little for that amount of light.

Since the Brute runs on d.c. the ballast is presumably a resistive one, so the power wasted in heating up the ballast is probably close to that used by the lamp.

Posted by Dave Macaulay (Member # 813) on 05-17-2012, 07:21 AM:

The GE mobile searchlight arc runs at 150A. Voltage is around 80VDC at the spotlight connection. Sorry but I don't know the fuel consumption for the generator. I recently saw one under a tarp at a house, and asked the resident about it. The carbons are a difficult to find and expensive.

Posted by Stephen Furley (Member # 1277) on 05-17-2012, 08:38 AM:

80 V sounds about right for a large carbon arc, but I'm surprised that the current isn't more than that. That's similar to an Ashcraft Super Core-lite projection arc, and less than a Baby Brute, which I think is 225 A, or thereabouts. I suppose that the light is concentrated into a much narrower beam than a Brute, so a given amount of light goes further.

Posted by Jeff Taylor (Member # 443) on 05-17-2012, 10:25 AM:

IIRC those mobile searchlights were gas powered, not diesel. I think it was a version of a Ford tractor engine. During wartime fuel consumption probably wasn't much of an issue compared to sourcing an "off the shelf" engine quickly.