I got into this “Cool Lights” business of mine because I thought prices were outrageous on pro level fluorescent fixtures. You can see all over this site the manifestation of what I decided to do about it starting with the Cool Lights video and ending with low cost fluorescent fixtures. Well, I’ve gotten the same feeling again on another lighting technology: HMI. I was searching for an energy efficient hard or point light source to complement our fluorescent Cool Lights Softlight Series product line and was learning about HMI as the natural solution. Crazy prices though and no good reason at this point to have them so high. Read on to find out more about what I’m talking about and how you can make an HMI fresnel for under $500 in Part One of a multipart article…
Coke or Soda?
Of course, we’ve probably all said at least once in our life, “I want a coke,” when what we really mean is, I want a soda of some kind. The tradename of Coke (a trademark of the Coca Cola Company in case you are from Mars) has so permeated our culture that now the tradename can be used in reference to a generic substance at large, namely all sodas. If you think about it, it’s interesting that they could be confused but we all know what is meant somehow when someone uses the “coke” term. The same thing has happened to a lesser extent in the smaller film and television lighting world with the term “HMI”. In this article, we’re going to talk about building your own low cost “HMI” type fresnel but first a bit of background as to why we are searching for a low cost alternative in the first place. And what is HMI anyway?
To start with, did you know that HMI (which stands for “Hydrargyrum Medium-Arc Iodide” Hydrargyrum is the latin for “mercury“) is really a tradename of the Osram Corporation and not referring to some proprietary technology? Nor does it refer to the ballast driving the bulbs either–I’ll talk more about the ballast in a bit though. Also, did you also know that other manufacturers make similar products under different names? Philips has “MSR.” GE has “CSR.” And so on…
Another fact, many film and television light fixture manufacturers ride on the coattails of this Osram trademark and make fixtures that use members from the technology family, but not necessarily the HMI bulb itself from Osram. They still call their fixtures an “HMI” and have been getting away with this for a long time. Perhaps many companies only used the Osram bulb and ballast solution in the beginning. It permeated into lighting specialists subconscious minds and then other competitors came forward with similar solutions and no one challenged it. It’s true that Osram was the first to make the technology behind HMI commercial; but it was Thorne Lighting of the UK which was the first to make a bulb like this. They weren’t successful at marketing it though at the time. In any case, there are clearly many fixtures now that use other brands of bulb but they still call them HMI’s.
Kind of the idea alluded to in the opening statement: calling a soda a “Coke” when it may in fact be another brand of soda and perhaps not even a cola at all. In addition, all the mystery surrounding the subject and the thought that HMI is some proprietary technology has only increased the perception by manufacturers and customers that it’s okay to charge huge sums for the fixtures.
HMI or HID?
What is the technology though that HMI and all its various look-a-likes use since HMI doesn’t describe a technology? In fact, they are all part of the metal halide family and more specifically the oldest family known as Quartz Metal Halide (QMH); a newer technology known as Ceramic Metal Halide (CMH) is even more advanced but both QMH and CMH belong to the larger inclusive family known as High Intensity Discharge (HID) bulbs.
Just for reference, the HID lamp family includes such diverse branches as sodium vapor and mercury vapor which are, for the most part, totally useless for film and video production because of their low color rendering indexes (CRI) and color temperatures; with the noted exception of the famous traveling matte sodium vapor process or “yellow screen” used by Disney studios until the digital age. You know that those two bulb types are mostly usable as street and warehouse lighting but some might even debate that. QMH or CMH lamps can be a big step up from the limited color temperatures of mercury or sodium vapor. This is because they can have CRI values up to about 95 (particularly CMH has a lot of promise in this area) with 80 to 90 very common and have a variety of color temperatures available. You can also have a tungsten colored, high CRI CMH bulb too! You can get tungsten colored QMH but the color rendering result is not that great.
So we’ve established though that the HMI is really the older technology QMH type bulb, but what are some of the other things which made the HMI so interesting to the film/tv world in the first place?
HMI as a Household Name in the Film/TV World
So what is HMI technology anyway and what makes it so great as the bulb of choice?
- Color Temperature 6000K. No it’s really not 5600K like many think! That’s just a myth. But some competitors like Ushio and Eiko do it the right way and make 5600K versions. What bulb is in that “HMI” you just rented? Interesting question isn’t it?
- CRI. HMI CRI is 85 or above and more often 90.
- Hot Restrike or “HR”. The ability to turn the bulb and fixture back on immediately after turning it off. The less expensive bulbs (NHR) will require that you wait about 5 to 10 minutes of cooling off before you can turn them on again. Very inconvenient but not insurmountable.
- Ultraviolet Shielding on the Bulb Itself. An outer glass shell that is UV protective. These bulbs emit UVA / UVB in varying quantities. HMI brand has UV shielding built-in as well as some of its competitors also do the same. Even with the UV shielding though it’s still not safe in an open face fixture.
What makes the “HMI” fixture that uses bulbs like Osram’s HMI so wonderful?
- Flicker free ballast. We’ll talk more about this later, but as with the fluorescent ballast world, we have a magnetic or an electronic ballast choice for CMH. Not that its impossible to find flicker with an electronic ballast (as with fluorescent also), but the chances increase greatly for a better experience. We’ll need to check the “output frequency” specification to be sure. Ideally, to be safe it should be measured in as high as possible a hertz value (beyond the mains frequency if possible) to avoid flicker.
- Hot Restrike. Not just a function of the bulb. The ballast ignitor must also be capable of this.
Given this information about HMI, we now know what we want to shoot for in building our fresnel–to make it as close to a professional-level HMI fixture as possible.
In the next part, we’ll actually acquire an old fresnel from somewhere like eBay, open it up, replace the appropriate parts inside and attach our ballast and new bulb.
Osram HMI Information “Osram Trademarks and HMI History”
Answers.com (wikipedia) “Hydrargyrum Medium-Arc Iodide”
Answers.com (wikipedia) “Sodium Vapor Process”
Einlightred “Light History”
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