There are a variety of different lights that are used in common digital video or film production. To produce the image that you want you have to have the ability to control the light that hits your subjects, at least in part. To do this you will use mainly artificial lights, often in the form of portable lights and kits. You may use softlights for less dramatic images, tungsten balanced fresnels for a warm spot, and reflector cards to guide existing light. On the higher end you are going to have HMI lights, which stands for Halogen Metal Incandescence. In the hierarchy of portable lights HMIs are on the end of the powerful elite.
HMI lights are generally used when you need a much more dramatic set of lights, which is standard on larger film or commercial sets. They run at Daylight temperature, which gives a much cooler color at around 5600 degrees. These are comparable to things like Fresnel lights, except that they are much more direct and intense.
There are two major issues when trying to use HMI lights. The first one is that they are incredibly expensive, which is why they are often regulated to larger productions. A single low range HMI light will likely run you several hundred dollars a day to shoot, which is unreasonable for smaller productions. The second issue with HMIs is that they are incredibly heavy. For smaller HMIs you can use a normal stand to go up and down, but you may need more than one person to move it and get it to go up and down. On larger ones you are likely going to have to use an automated type of stand that can pedestal up.
HMI lights can be an efficient use of power as you often can use an intermediary box and simply plug them into the wall. If you are using larger HMI lights, like over 10,000 watts, then you are going to have to create alternative situations.
HMI Lights on Your Set
HMI lights will actually solve a number of the problems that people have getting enough light in a normal area. They are commonly used for outdoor lights at night, especially coming through windows and lighting large open areas. For the same power, an HMI light is going to be much more powerful than most comparable lights. They are not usually going to have a warm look, which comes with Tungsten balanced lights at 3600 degrees. Instead it often looks artificial, which is why it is perfect to light up spaces and mimic street lights or those found in cities or on ports. If you do want to give it a warmer look you are going to have to go ahead and gel it, which requires a special set up as you cannot get too close with normal gels to the HMI bulb.