Thanks, I really appreciate it. But now I have some follow-up questions.

If the CDM is so much better in your opinion, why is it less money than the HMI?

Flags are like barndoors except usually larger. Soft light is usually soft light because it is being emanated from a large surface area as opposed to a hard light which is usually emanating from a small and concentrated point of light. Because of this and the diffusion effect which scatters the light more, it requires a much bigger barndoor then you can practically fit on a fixture to control where the light is going. For this reason, flags (or eggcrate filters are another way) are like large pieces of foam core or some flat, thin, non-reflective and opaque material that can be placed on the sides of the light to control its side spill. An eggcrate filter can do the same thing too but there is some loss of light. This filter directs the light only forward like a "garden hose" effect and keeps side spill to a minimum as well.

Flags are just one kind of light control. You have eggcrates, as I mentioned, scrims which are like screens of varying density which are used to cut light intensity, diffusion materials of various kinds and grades which are used to diffuse hard light.

Dimmers are another. Of course, with ballast-oriented lighting like fluorescent, HMI/CDM you must have a ballast that dims to be able to do that and can't dim them with an external dimmer like you can tungsten.

HMI has classically been expensive because a very few companies controlled the production of the fixtures and its mainly used in stage/studio lighting which is a very small market. Only one company actually produces an "HMI" bulb and that is Osram. Other clone bulbs exist but it would be technically incorrect to call then an "HMI" since that is a registered trademark of Osram.

In fact its always incorrect to call any fixture that uses HMI or its clones an "HMI" and would be better known as as a metal halide fixture. Getting people to change will never happen though as its engrained into our industry to call them that. HMI is in fact simply another flavor of metal halide as is CDM. HMI has a hot restart capability which means it can relight instantly whereas CDM needs to cool down for about 5m or so before you can relight it. That is one of the main differences and is mostly behind the life issue. HMI's hot restart is murderously hard on bulbs, ignitors and ballasts and a price has to be paid to have that capability.

In addition, CDM happens to be more available on the market for commercial use in stores and warehouse lighting and as such will therefore be more widely available and less expensive than HMI derivatives which are a very specialized class mainly for use in the entertaiment field. Most large studios in Hollywood capable of buying HMI class fixtures are operating off of megabudgets and are not concerned with the price of a fixture, the bulb price nor about bulb life. I think most aren't particularly concerned about energy efficiency either. They choose HMI fixtures because of the ability to fight or simulate daylight when they need it. They also like to be able to relight instantly too since they are most concerned about the time vs money issue. Thus, perhaps another reason why price hasn't come down on the HMI class of fixtures.

Is the light coming out of them virtually the same (watt for watt)?

Also, what's the largest CDM you guys carry (watts)? I saw a 650w on your site I think, but is there anything larger?

We have two classes of hard lights for sale: tungsten (very conventional) and CDM/HMI. Tungsten is just what it is: inexpensive to buy but more expensive to operate over time given relatively short bulb life, hot fixture, hot light output, requires a fair amount of air conditioning to displace the heat, etc. There is no ballast in these units. Just a bulb and the fixture. The bulb operates directly off of your line voltage in your house/studio. You can dim it with an external dimmer too.

The CDM / HMI class are like fluorescent in that they use a ballast as a special power supply for the bulb which has a discharge chamber in it and when it ignites, the chamber is where all the lighting action happens. Without the ballast and whatever capabilities it adds (like dimming) you can't make the fixture work so the two are inseparable. The ballast / bulb combo buys you a four to one leverage in general for energy use: a 150w CDM is roughly equal to a 650w tungsten light for instance. Said another way: the CDM 150 draws 150w to put out about the same light as the 650w tungsten fresnel which is really drawing 650w and radiating 650w worth of heat too. The 150 radiates around 150w of heat so its a bit hotter than a fluorescent but also more intense and capable of better projection and definition too. The light from both is very hard and of the same general quality but the CDM 150 is capable of "daylight" color without gel whereas the 650w tungsten needs a gel to make it daylight and looses a bunch of light output in the process (as much as two stops).

Some people feel there is a difference in the quality of light between a tungsten unit and a discharge unit like fluorescent or metal halide. That's a whole other subject relating to the spectrum of light it puts out, etc. You have many people using fluorescent or HMI/CDM every day though and liking what they do so it is purely a personal preference to prefer tungsten use over discharge. In addition, there can be some green tint effects for those that use actual film in their productions and those people use a minus green filter to filter out the effect. For those using digital mediums, the capability to white balance keeps any green issues minimized to practically nil.

The largest CDM we currently carry is a 150w but I also have a 575w HMI in beta test right now limited release and a future 1200w hmi coming as well as larger CDM units like a 250w and 400w.

Richard, it's starting to make a lot more sense now. Thanks for taking the time to explain it.

Are the CDM150's the biggest CDM you have? Lumen for lumen, they are close to the equivalent of a 650w tungsten then, right? Do you have a CDM equivalent of a 1k tungsten?

Also, Richard, you mentioned the CDM needs a special dimmer. Is that included in the ballast provided with the light? Can the CDMs be dimmed down?

I would add that I have purchased from Richard and the quaity of the stuff he sells it top notch. His products are good value for the money. No cheap plastic stuff.

Yes, the 150 CDM is the biggest in that class (for now) with 250 and 400 to come at some point later. And, yes they seem to be about lumen per lumen the same output as a 650w. You can't dim the current models though. I could have done that but it would add quite a bit to the cost. We can offer a more expensive ballast at some point in the future as an option, but for now we thought keeping the cost down was an important feature. Even with the more expensive ballasts you can't dim metal halide of any kind including HMI beyond 50%--its just a limitation of the technology. Any fixture that claims to dim more than that has some other trickery, usually some kind of mechanical shutter system or some such thing. What you would probably see from us would be a 1/2 intensity switch or some similar arrangement.

Ok, thanks again. Is it possible to "dim" a light like that with some gels or something without loosing the "hardness" of the light like with diffusion?

Yes--that's what scrims are for.

Bill, Richard, and others... you guys are awesome! Thanks for all your help with this.

With scrims, just the intensity of the light is lowered, but not the color temp?

Right, all "mechanical" methods of dimming (like scrims or diffusion material) are color temperature neutral whereas most all electrical dimming will entail some color temperature change.

Okay, so I think I have this all figured out now. I appreciate all the input from everyone. Now that I think I have all the differences figured out, I'd like to know what you recommend me getting.

I have basically two sets.

1. One head-to-toe greenscreen
2. "fireside chat" with stories being read to two kids in a living room.

Now that I know I want florescents and CDM/HMI type lighting, what should I buy exactly and how many? Would posting a picture of the "set" and the talents be helpful?

THANK YOU!!!!

Probably wouldn't hurt to see a picture or at least know the size of the area. That way it would be easier to recommend a certain quantity of lights.