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Bright enough to be used outdoors as a key-light—a 400-watt HMI is easily the equivalent of a 2k quartz lamp beamed through a dichroic filter—the HMI has become a necessary (albeit expensive) part of even the smallest location lighting kit. HMI lighting fixtures offer two significant advantages over other luminaires. They are more efficient, providing more than four times the light output of similar-wattage tungsten lamps, making them a perfect choice on locations where power is limited; and they burn at 5600K, allowing them to be easily mixed with sunlight without the need for color correcting filters. But these advantages aren't all that set HMIs apart from their tungsten kin. There are some minor disadvantages too. Here are a few operating and safety caveats; things to keep in mind whenever you use an HMI.

  • • Lamps are expensive, like hundreds of dollars each. So pack the head carefully. Don't drop it. And always sandbag the stand to keep it from getting kicked or blown over.
  • • Pay careful attention to the condition of the cord and connector(s) between the ballast and the light head. That lightweight power unit boosts household juice up from 110 or 220 to several thousand volts. A frayed cable or a connector that is no longer firmly secured to the cord isn't just a potential problem. It's a serious shock hazard.
  • • Allow at least a minute of warm-up time for the arc to reach full brightness and the color temperature to settle down. And beware of the lamp that won't stay lit. If you can't strike an arc or if the light shuts off repeatedly, the bulb may have reached the end of its useful life.
  • • Finally—and this is really important—don't ever operate an HMI lamp without the manufacturer's safety glass firmly secured in front of the bulb. Just like the sun, HMI arcs radiate a high level of ultraviolet light. So much UV, in fact, that a bare bulb can burn the face and eyes of your subject.