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HMI and metal halide


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#1 clyde villegas

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Posted 10 September 2008 - 11:19 PM

Is HMI the same as metal halide? Can I substitute Metal Halides for HMIs? I find them relatively cheap at Hardware stores.
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#2 Richard Andrewski

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Posted 11 September 2008 - 12:50 AM

HMI is only a trademark of Osram and is a member of the metal halide family but not close enough to substitute directly in fixtures or ballasts. I call the other non-HMI "commercial metal halide" because it tends to be used in architectural / building spots, retail situations as a replacement for tungsten, etc.

The things that really separate them are the following:

- HMI and its clones use stage lighting type bases / sockets like GX9.5, GY9.5, G22, G38, etc., whereas regular commercial metal halide will use less expensive alternatives like G12 or E26 / E40 type screw in sockets. There are double ended versions in both groups too.

- HMI bulbs are very compact and commercial metal halide tends to be bigger and a bit less of a point source. Harder to put into a stage/studio lighting instrument and get the effect you want.

- HMI is always 6000K color temperature across the whole bunch of bulbs. There are some exceptions in Osram clones that are at 5600K but most find there isn't enough difference between 5600K and 6000K to worry about it. They are also generally high CRI of 85 or above. Commercial metal halide generally tops out at 4000K and is generally low CRI of 60 to 70 (there are exceptions though).

- HMI bulbs are hot restart as long as the ballast/ignitor going with them is also capable of that. Commercial metal halide is almost never hot restart. HMI bulbs are lower life of 1000 hours or less because of this hot start capability and commercial are generally higher lifetime of 2000 to 12000 hours. The size of the bulbs also affects their lifetime. In general the larger bulbs have the longer life due to heat considerations.

- HMI bulbs are more expensive because of the quality control and color temperature/CRI testing considerations they have to go through. Commercial metal halide are used in places where the 60 to 70 CRI is not considered to be super critical. There are exceptions of course. Iwasaki Electric makes some very high quality commercial metal halide that rivals HMI in CRI but the price is quite a bit higher and their color temperatures are usually jumping around from 4000K to 6500K without the nice versions in 5600K to 6000K to match other lighting we use often in film/video.

You can convert a tungsten fresnel to a commercial metal halide type with a bit of work and I've shown how to do it before in an article I wrote but you have to pick and choose the bulb / ballast combo pretty well to get what you want out of the finished product. Hope this helps.
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#3 Richard Andrewski

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Posted 11 September 2008 - 01:08 AM

One other point I forgot was that the ballasts, while sharing some common traits are different between HMI and commercial metal halide. The ignitor will typically be separate for HMI ballasts to allow a long cable length. The ignitor will often be integrated into the ballast with commercial metal halide meaning that cable length has to be kept fairly short. You can find exceptions on both sides though as far as where the ignitor is placed.

There are other considerations too about the frequencies that the different bulbs require to operate as well as voltage and current levels.
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#4 clyde villegas

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Posted 17 September 2008 - 01:57 AM

I've shown how to do it before in an article I wrote...


Where can I see that article? Can you send me a link? Thanks and God bless.
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#5 Richard Andrewski

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Posted 17 September 2008 - 02:24 AM

Where can I see that article? Can you send me a link? Thanks and God bless.


Sure. It's in my blog here:

http://www.coollight...tegory/articles

4 part article written in 2007 showing how to build a metal halide fresnel for under $500.
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