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Old January 20th, 2005, 02:49 PM   #1
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What do HMI & PAR mean?

Hi!

Can anyone tell me what HMI and PAR stand for? And: does VMI lighting exist?
I have a customer asking for it, but I don't want to appear stupid asking whether it's a typo.....

Thanks!

Dan.
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Old January 20th, 2005, 03:08 PM   #2
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HMI- Hydragyrum Medium Arc Iodide
PAR Parabolic Aluminized Reflector

That's all I got
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Old January 21st, 2005, 03:20 AM   #3
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That's what the initials stand for. In case you don't know what they do, HMI's are a certain type of light, just like fluorescent and tungsten are. HMI's are kind of like a half-breed between fluorescent and tungsten: they use ballasts and burn like a fluorescent, but the light is a pinpoint hardlight like tungsten. The light they produce is daylight-colored rather than tungsten-colored, and they're hard lights, rather than fluorescent's inherent softlight qualities.

PAR is shorthand for stating that a light fixture uses a parabolic reflector. The design of the lamp focuses more light forward, and when focused down tightly, they can throw that light quite far and efficiently.
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Old January 21st, 2005, 03:29 AM   #4
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You guys ROCK! Thanks!
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Old January 21st, 2005, 04:44 AM   #5
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Don't forget that HMIs are super sweet because they output 4-5 times the same amount of light as an equivalently watted tungsten light (e.g. a 1200 watt HMI will output about the same amount of light as a 5K tungsten, and you can plug that HMI into a household fixture). Also don't forget that they're expensive as hell. As are their bulbs.
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Old January 21st, 2005, 01:04 PM   #6
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<<<-- Originally posted by Josh Bass : Don't forget that HMIs are super sweet because they output 4-5 times the same amount of light as an equivalently watted tungsten light (e.g. a 1200 watt HMI will output about the same amount of light as a 5K tungsten, and you can plug that HMI into a household fixture). Also don't forget that they're expensive as hell. As are their bulbs. -->>>

Well, yes, there is that whole angle too. On a raw lumen basis, comparing an HMI fresnel against a tungsten fresnel, the footcandle advantage seems to be about 3x. However, because the light is a different color, you have to factor in the effect of color-correction gels.

Gelling a tungsten light to 5600k costs about 2 stops, so a 2k tungsten fixture with CTB gel on it is going to deliver about 500 watts' worth of usable blue light. A 200-watt HMI is going to put out the equivalent of about 600 watts. So you'll get more net footcandles for 1/10 the wattage (and 1/10 the heat!)

When going for tungsten-colored light, you use CTO gel on the HMI's, which robs you of about 2/3 of a stop. So a 1200w HMI with CTO on it is going to deliver as much tungsten-colored light as a 2400-watt tungsten light would.

So HMI's have some serious advantages over tungsten, but there are also some tradeoffs. HMI's are less convenient to use, the affordable HMI's use magnetic ballasts which are big, heavy units you have to haul around... a 1200w HMI's magnetic ballast weighs about 75 pounds! Plus you have to wait for them to warm up... with tungsten you can pretty much turn on the light and start shooting, with HMI's it can take 10 minutes for them to warm up and come up to full brightness and proper color temperature. Then there's restrike time... with tungsten you can turn a light off, move it, and then turn it back on, no problem. With mag-ballast HMI's, you have to wait around 10 minutes from when you turn it off to when you try to turn it on again -- no off/on is allowed. And when you turn it back on, you've got to wait for it to warm up again...

Electronic ballasts can solve those problems, but they're *much* more expensive.

As for cost, depends on if you want new or used. Used 575-watt HMI's with magnetic ballasts aren't all that expensive, usually complete systems selling on ebay for under $700. But for a new one, with a new electronic ballast, you're looking at more like $3,000 to $4,000.
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Old January 21st, 2005, 01:45 PM   #7
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Alright, well, let's say 3-5 times as powerful as a tungsten, depending on who you ask and other factors, then.

Also, with the CTO/CTB thing, if all your sources are HMIs, no gelling needed.
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