Following on from last week’s look at tungsten units, today we focus on HMI lighting. HMIs are more complex technology than tungsten, meaning they are far more expensive, and more prone to problems, particularly if you get a deal from a hire company and they give you older units. But they are bright and relatively efficient and because of this, and their colour temperature of 5,600K, they are by far the most popular type of light used in today’s film and TV industry when battling or mixing with natural daylight.

HMIs (hydragyrum medium-arc iodide) operate by creating an arc between two electrodes. This arc excites a gas which produces the light. In order to ignite the arc, a ballast is required. This device also regulates the current, while a special header cable connects the ballast to the light.