by Steven T. Smith

Lighting for Video- Part IV

This is the chapter where lighting for video takes an exotic and expensive turn, for here we visit the Hydragyrum Medium arc Iodides– the fabulous HMI's. Watt for watt, these fixtures are two to four times brighter than their tungsten equivalents. In the past quarter century their use has revolutionized motion picture photography.

Though the principle behind the HMI has been known for decades, it wasn't until the late 1960s that lamp developers turned their attention to applications for film and video. At the request of German television (seeking, ironically, a less expensive alternative to incandescent lights), the electrical giant Osram began work on HMI bulbs.

I encountered my first HMI on a Hollywood soundstage in 1974, two years after its introduction. It was an impressive luminaire, but those early models had a number of drawbacks–not the least of which for a cinematographer was the "flicker problem."

HMI lights are ballasted sources (as are common fluorescents), which means they pulse on and off a fixed number of times per second– that is, they flicker. If you're shooting film at 24 frames per second, or video at 30 frames (60 fields, corresponding to the frequency rate of the electrical source, 60Hz) you won't see the flicker. But if you take your 30fps NTSC camcorder overseas, where the power is 50Hz, there will be a pronounced flicker (which, incidentally, you can make disappear by setting the camera's shutter to 1/100th second).

The flicker problem with early HMI's mainly affected cinematographers who wanted to shoot at non-standard frame rates or shutter settings. The introduction, about a decade ago, of electronic "flicker-free" ballasts means that cameramen can shoot at most any speed they want without worry. This issue has little bearing upon the video photographer, except that the new ballasts weigh a fraction of the old magnetic versions, and hence, for the first time, location use of HMI's became feasible.

The main drawback of HMI fixtures is their cost. Whereas a 300w Arri Fresnel costs less than $300, the 200w Arri HMI costs over $2000– costs, in fact, about as much as a Canon GL1. With prices like these, why use HMI in the first place?

Because the light they put out looks gorgeous.

First of all, HMI's are daylight balanced– their output is 5600 Kelvin.

Second, and most important, the light from HMI's seems to have the ability to "wrap around" objects and subjects (at least that's how many DP's describe it); seems to fill space with bright, happy light. I know that sounds pretty corny, but after you've worked with incandescent light– that warm 3200 Kelvin stuff– the cool, bright illumination of an HMI seems revelatory. Okay. You got to see it and work with it to fully get it. So, let's work with it.

When to use HMI's?

They are especially well-suited for exterior work. Shooting on a shady patio with a bright background and no direct sun off which to bounce a reflector? A 400w or 575w HMI fixture will balance the subject with the background, while adding some definition to the face.

Shooting against a blown-out sky and want to see your subject's face? You'll need a big guy, at least a 1200w, and maybe a 2500 or 4k. Be aware that when you go above 1200w you'll have to arrange for some appropriate power– a standard household 15A or 20A circuit is going to get blown sky high (and perhaps the house along with it) so do be very careful.

BTW. When shooting exteriors here are a couple of tricks you can use to make any situation look better, even if you don't have HMI's on hand:

To smooth out direct, overhead sunlight (i.e., that ugly kind that makes your subject's eyes disappear into black sockets) you can insert some diffusion between the great orb and your subject. In the industry these are called "silks." A piece of Tough Frost, or even a white sheet will do the trick. The folks at Chimera make a lightweight frame and fabric system perfect for this purpose. It can be handheld or mounted to a light stand. In a pinch, I once even used an umbrella. We were shooting an interview at an elephant farm in southern India. The subject looked awful under the merciless equatorial sun, so I begged a bystander to hold his black brolly over my chap's head. Instant diffuse light. Yes, I lost a couple of stops on his face, however the background was not so bright that it overpowered the foreground.

But what if that BG had been too bright? An easy trick for such situations is to run a couple of yards of back scrim right across the background. Yes, it's in the shot, but if you smooth out any wrinkles and keep it back far enough, the camera won't know its there. I usually carry a small bolt of double scrim (equivalent to a full f-stop) for this purpose. You can buy this material from Matthews, or you might find a suitable substitute at a fabric shop.

What about using HMI's indoors?

If you're shooting in a room full of windows, HMI's are a great way to go. Remember, that a 400w fixture is going to put out more illumination than a 1000w tungsten light. I can often get away with using a single HMI to do an interview in such a setting– employing a bounce card for fill. The biggest HMI job I ever had was lighting a high-profile two-camera interview with Woody Allen for "60 Minutes." The location was his penthouse suite overlooking New York's Central Park. And of course, there were huge windows on three sides. We had to consider not only lighting Woody and correspondent Steve Kroft perfectly, but also take into account the sun, which would move from one side of the flat to the other, during the course of a long interview. We ended up using three 1200w Arripar fixtures bounced into 4x8 sheets of foamcore (which also helped to block light coming in from the windows). Fill was provided by a couple of heavily-diffused 200w Joker lights. Then, to light the background, I used a single 575w fresnel. In the end, it all looked great. It was one of those jobs that could not have been done in that setting and at that time of day with standard tungsten lighting. Hooray for HMI's.

Now, I know you're not going to run out and buy these things. A small set of small lights can set you back $10,000. But when you really need the punch and wrap-around light of an HMI you can rent them. A 200w Joker might rent for $35-50 a day; a 1200w PAR for $75-125. Renting will not bust your budget, and will help give your production a very polished look (it will also make shooting possible in otherwise impossible settings).

For the next installment I'd like to hear from you– your questions or comments– on any and all things lighting. I'll do my best to provide illuminating answers.

Steve Smith

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