Magazine article American Cinematographer

Metal Halide (Hmi) Lighting at Photokina '74

Magazine article American Cinematographer

Metal Halide (Hmi) Lighting at Photokina '74

Article excerpt

Metallogen lighting has been a long time coming, but ten equipment manufacturers demonstrated their faith in the principle by displaying examples of such lights at Photokina

On the basis of sheer space, probably more area at Photokina '74 was devoted to lighting equipment manufacturers than any other particular aspect of professional motion picture equipment. And of all the lighting equipment being displayed there was no doubt that the new Metallogen or metal-halide type lights were receiving the greatest attention. These lights, which employ the HMI lamps, are probably the biggest breakthrough in lighting technology since TungstenHalogen was introduced. The name of the game is efficiency and the HMI lamps can put out three to six times more light than an incandescent lamp of similar wattage.

An incandescent lamp works on the principle of heating an element until it glows. Unfortunately only about 15% of the energy put in comes out as visible light. The other 85% comes out mostly as unwanted heat.

The new HMI lamps are actually miniature arcs inside a small quartz bulb. The HMI bulb can achieve efficiencies of 45%, about three times greater than an incandescent. Moreover, the HMI lamp emits a light spectrum almost identical to that of daylight. Since incandescent sources lose about 50% efficiency when filtered to daylight color balance, the HMI has almost six times the output of a daylight (blue) filtered incandescent of similar wattage.

What this boils down to is that a 12'00-watt HMI lamp will put out almost as much light as an incandescent 5K. Under daylight balance the 1200-watt HMI will put out the remarkable equivalent of 7000 incandescent watts.

The HMI lamps require a special ballast to facilitate operation. The ballast box accomplishes two things. It provides a very high voltage for ignition (as high as 65,000 volts) and a constant current regulation during operation.

The Cremer lamps, which are made in France, are particularly interesting, since they can be converted from HMI to incandescent by simply changing the lamp head tray. Thus, the 4000-watt HMI can become a 10,000 watt incandescent in the studio. Likewise, the 2500-watt HMI becomes a 5K incandescent; the 1200-watt HMI, also a 5K incandescent; and the 575-watt HMI becomes a 1K incandescent. These ratings are 6000°K for the HMI lamps and 3200°K with incandescent bulbs.

The laniro line of HMI lights is called the "QuartzColor Daylight" series and is comprised of 575-watt, 1200-watt and 2500-watt units.

The laniro units are focusable fresnels with about a 10-to-1 spot-toflood ratio on axis. They incorporate hour meters into the housing. This is a nice feature, since HMI bulbs drop 1°K of color temperature per hour of use. Even though the bulbs will last close to 600 hours, the service life is usually considered about 200 hours, after which color temperature degradation becomes excessive.

In most cases, the ballast weighs between two and three times as much as the lighting head. For example, the laniro 575-watt head weighs 6.4kg and its ballast 12 kg. The 1200-watt is 13 kg and 18.5 kg respectively, while the 2500-watt package is 15.2kg and 29 kg.

Kobold has introduced a line of lightweight reflector type units. The series consists of two 575-watt units, a 1200-watt unit and a 2500-watt unit. One of the 575-watt units, Model DL 575, is fixed-focus, while model DLf 575 is focusable. Model DLf 1200 and DLf2500 are both focusable. The weight specification for these Kobold units definitely verify their compact lightweight appearance: DL 575, head 3. …

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