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Old September 30th, 2008, 10:17 AM   #1
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cdm/hmi

Hey everyone, I'm thinking about picking up a non-tungsten hard light. I don't like how tungstens get so hot and make actors sweat. I've been looking at these CDM/HMI lights (for instance, CL-MF0150 Cool Lights CDM Fresnel - Cool Lights USA), and I don't fully understand what's up with them. Is CDM a kind of HMI? They seem like they'd be perfect -- less heat, use less juice, and 2 different color temp bulb options to boot. But if they're so perfect, why are people still using tungstens?

I also heard someone say something about not being able to shoot 24p 1/48 with these lights -- have to set the shutter speed to 1/60 to prevent flickering. Anyone know anything about that? Any other concerns I need to be aware of before plopping down $500 for one of these?

thanks,
Josh
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Old September 30th, 2008, 10:42 AM   #2
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I'm sure customers of mine will chime in. To answer one question: CDM vs HMI. CDM and HMI are part of the same, larger metal halide family. CDM belongs to a class I call commercial metal halide and is typically found in retail use, architectural use and other similar uses. Most of the lights in this class would be unsuitable for use in a stage/studio fixture but we have picked and chosen from some of the best we've found to put into usable fixtures.

In other words, these bulbs won't have the quality control of an HMI which goes through strict testing but then they don't have the cost structure either. They can use a bit simpler ballast than an HMI and are also cold start normally too which means you have to let them cool down for about 5 minutes after you extinguish them before you relight.

I think while most would prefer everything to be hot restart, as with HMI bulbs and ballasts, but the simplicity and lower cost of a CDM serves the budget conscious well and gives many of the advantages that you would seek in an HMI anyway.

Back in 2007 I wrote 4 articles in my blog about how to make a metal halide fresnel for under $500 using an old tungsten fresnel. This was our manifestation of that into an actual product showing that it can be done for under $500 -- to have something very close to a 150w HMI in most behaviors.
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Old September 30th, 2008, 11:29 AM   #3
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This is really interesting. So let me see if I got this right. HMI is high-quality, but crazy expensive. (A quick look at the Arri HMIs at B&H confirms this -- they're just under a hojillion dollars.) But you managed to find a cheaper route that looks just as good: CDM. The drawback is that you have to wait 5 minutes before powering them back up. Is that the only drawback? No flickering/shutter speed issues?

That sounds like a great trade-off to me. Now, what happens if I restart the light one minute after I shut it off? Does it break? Or just not work? I can see it happening by mistake pretty easily.
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Old September 30th, 2008, 02:29 PM   #4
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You have to be a little more careful is all. Even when using HMIs that are hot-start, you don't turn them off and on like you do quartz lights. It takes a few minutes for one to warm up to temperature, and the more "striking" you do, the harder it is on the pricey bulb. If you shoot with fluorescents, it's a similar thing--they take a little time to come up to speed. So for me, a 150 watt CDM that is basically indistinguishable from an HMI, when the CDM is 500 bucks or less, and the nearest HMI is over $2K...well, that decision is a no-brainer.

I used a set of Altman 650 watt fresnels for a few years (two 650s and two 300s), and these 150 watt CDM fresnels not only look just like the Altmans, they should put out about the same amount of light with the same level of control, only they're daylight. I'm lighting most things daylight these days because I think the camera looks better that way, using mostly LEDs. I'd like to get one or two of these fresnels in the near future when budget/situation (need) permit. Much better than using CTB gels on tungsten lights to match with my LEDs.
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Old September 30th, 2008, 06:17 PM   #5
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Quote:
Originally Posted by Joshua Csehak View Post
This is really interesting. So let me see if I got this right. HMI is high-quality, but crazy expensive. (A quick look at the Arri HMIs at B&H confirms this -- they're just under a hojillion dollars.) But you managed to find a cheaper route that looks just as good: CDM. The drawback is that you have to wait 5 minutes before powering them back up. Is that the only drawback? No flickering/shutter speed issues?

That sounds like a great trade-off to me. Now, what happens if I restart the light one minute after I shut it off? Does it break? Or just not work? I can see it happening by mistake pretty easily.
I don't know about the shutter speed issues. I never saw a problem with that. For anyone thats interested, the output frequency is about the same as most normal metal halide / hmi frequencies and that's about 140 hz which puts you out of the range of issues for most normal shutter speeds except for some of the highest ones perhaps. There's a shutter speed calculation formula which I can post if necessary to help you. Its useful when you're dealing with a discharge type light that you think you might have an issue with. As long as you know the frequency of the output voltage driving the light you can calculate safe shutter speeds. In most of the cases where its an issue the output frequency is in the 50 to 60 hz. range.

On the issue of what happens when you turn off and then back on its simplified in the case of the CDM 150. Theres a timer on the switch that enforces 6 minutes. Turn off the switch after the light has been on. Turn on the switch again immediately. Nothing happens. You may think the light died but it didn't. This is simply a bulb and ballast protection feature. Leave the switch on and in about 6 minutes, the light will come on by itself. Not all CDM type ballasts have this feature--I wish they did as its murder on the bulb if its not hot start capable and you do restart it before with most ballasts. We have a 1200w cold start ballast in test that doesn't have that feature and its not good to turn the ballast back on without waiting. So, this is a feature to know about beforehand so you don't assume the light is broken when it doesn't come on immediately.

One other behavior of metal halide in general (CDM or HMI) is that the bulb comes up to speed over a minute or so. Gradually flickering, making strange noises, color variations and finally just a stabilized white light. Again, if you didn't know about all that beforehand and it was your first time, it might be surprising to you.

In general, the benefit of metal halide is that while it does get hot at the fixture level (and based on the real wattage draw of course) the light output is "cool" to the talent in front of the light as opposed to tungsten which has quite a bit of infrared in the beam.

CDM was our answer to wanting something efficient and cool output, daylight, a technology similar to fluorescent in some ways, but for the hard light domain--which fluorescent could never do no matter how hard it tried...
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Old October 5th, 2008, 09:31 PM   #6
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I'm sold. I ordered one of the 150w fresnels last week. Can't wait to try it. I'll post a quick review after I do. In the meantime, I found someone else's review:

Going Cool - Lights From Coollights.biz
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Old October 6th, 2008, 08:13 AM   #7
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Thanks for your business. Yes Ryan's done a lot with those fresnels and also has one of our 575s too.
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Old October 12th, 2008, 08:33 PM   #8
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Watching the 150W cycle through the different colors is pretty cool to watch.
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Old October 13th, 2008, 02:07 AM   #9
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Yes it is. Kind of a like a carbon arc miniaturized and sealed in a bulb so to speak. Not really solid state but the next best thing. And none of the noxious vapors of an open carbon arc either.

I think small wattage (35w to 50w) Xenon bulbs hold a lot of interest for a tiny pepper fresnel too and we have been looking at that. If we can just get that CRI up there a bit, we'll have one and then before you know it we'll have the ability to have a hard light fresnel (or par for that matter) kit, low heat, energy efficient, long life bulbs all for a surprisingly low cost.
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Old April 30th, 2010, 01:03 PM   #10
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Just wanted to post a mini-review cause I said I would, even though it's like 2 years later.

I was hoping to methodically compare it to a tungsten fresnel, but every time I rent one, I'm so tired from the shoot, that doing a comparison is the last thing I feel like ;)

But here's my impression after using it for a couple years: A+. The ballast makes a little buzz at first, but that goes away after a couple minutes, and it's really whisper quiet. If you can't wait that long (which isn't too much longer than the light takes to cycle up), you can stuff it under a pillow (the cord is long enough). The quality of the light is beautiful, the color is great (the daylight bulbs feel a little warm, i usually throw a 1/4 CTB on it to bring it to 55k). Build quality is satisfactory. It doesn't feel quite as rock-solid as an Arri fresnel, but I haven't had any troubles with it yet, aside from the lens getting cracked when I loaned it out. Which brings me to another point: Richard's replacement lens was $12. Arri's is $40. Nuff said.

What I love about it:

- Doesn't put out much heat. The savings in terms of comfort of talent and crew are enormous. Even in the spring, a tungsten fresnel can heat up a room enough to make everyone sweaty and stinky, and make the makup artist have to reapply the actors' makeup between takes. The CDM150 only heats up the room a tiny bit more.

- Only draws 150 watts. I can plug it in anywhere and not worry about blowing a fuse. Huge time savings.

- Optional daylight-balanced bulbs. I successfully faked morning once (shooting at night) by shining my CDM150 through one bedroom window and my kino diva through the other. Granted, I had to set the ISO to something like 1600, but it turned out great.

- Reasonably priced! Probably gonna buy another soon.


What I don't love:

- Have to wait 5 minutes to turn it on after you turn it off. The only time this is ever a real problem for me is when I have to fake turning lights on when an actor flips a switch. So if I see a script calls for that, I'll just rent a tungsten.

- Not dimmable. But tell you the truth, there hasn't been one time where I wished I could dim it. The scrims have always done the trick.


100% recommend it. And if you do any shooting indoors in the summer, it's a must-have.
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Old April 30th, 2010, 04:29 PM   #11
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Good to hear from you again and thanks for that. Really a better review anyway as you have experience enough to say what you like and don't like after almost 2 years. Of course hot restart is always better for some things if you can go that route but it does add enormously to the complexity and cost so that's why we felt the CDM alternative was a good one to bring to the market at a reasonable price because it can be used in many situations with no issues about whether you can relight instantly or not.
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