I built some DIY HMI lights and people want to know how I did it. Here's how.

First, the acronym "HMI" is not really a "type" of lighting, it's actually more of a name of a product. It's just been generalized like saying "googling" instead of "searching" when looking up something on the internet.

HMI lights are actually arc lamps from the metal halide family. These work by drawing an arc between electrodes, through a glass/ceramic/crystal envelope filled with different types of gasses and metal salts, collectively known as halides. The arc provides the power and the majority of the light, the metals and gasses change the color and spectral makeup of the light.

These bulbs need something to create the arc and then keep it regulated. These are the ignitor and ballast. The ignitor causes an initial spark to jump across the electrode gap and the ballast is a transformer that regulates the current that flows through the arc, sustaining it without letting it get too powerful or too weak. Each bulb needs a specific ballast. These usually have ANSI codes so that you can match them up. Don't expect to be able to mix and match the bulbs and ballasts. Also, don't expect to be able to get a more powerful ballast and get more light from a specific bulb, these don't work that way. There are some hacks you can do but they usually end up with very shortened bulb life or extremely hot ballasts that could catch fire.

With that said, Metal Halide lights are more efficient than tungsten. In fact, they are about 4.5x more efficient and give off very little heat. So for a 650W tungsten light, you are looking at 5.4A@120V. For the 150W MH you get the equivalent of 650W of light for 1.25A@120V.

So I started by making a small HMI type light. I gathered these parts:

6" Fresnel fixture
150w Metal halide bulb, G12 base, 3000K temp (needed M102/M142 ballast)
M142 ballast kit (ignitor, ballast, capacitor)
G12 bulb base

I bought a couple 150w bulbs. I got one from Coollights, one from GE, one cheap chinese one, and a Philips CDM. I wired everything up on the bench first and then started it up. These lights take a couple minutes to heat up and stabilize in color since they are not "hot-start". Everything worked and this light was incredibly bright.

I then modified the Fresnel fixture by removing the old bulb socket and drilling a couple holes in the bottom of the reflector/adjustment slider. I then maked some stand-offs with old aluminum tube so that the bulb would sit at the right height for the reflector.

I used this setup to test the different bulbs. I found that they all had very different colors even though they were all supposed to be 3000k temp. Most were very blue/green, especially the cheaper generic bulbs. The GE was a little better, but the Philips CDM was by far the best match for tungsten lighting. It still has a slight green hue but I added a 1/8 or 1/4 Minus Green gel and I could no longer tell the difference.

I found a nice cheap aluminum box to house the wiring, ignitor and cap and then mounted the ballast so that the majority of it was outside the box for cooling purposes. As long as the coating and paper on the ballast isn't damaged, it won't shock you.

That's all the time I have right now to type this up. I'll get some pics up in the next couple days!