A kilowatt is a unit of electrical power equal to one thousand watts, and is used in photography primarily in the context of describing the power output of high intensity studio lighting equipment, particularly tungsten and HMI continuous light sources used in professional studio, film, and television production environments.
In studio photography and cinematography, the kilowatt rating of a light source gives an indication of both its power consumption and, broadly, its light output. Large tungsten fresnel spotlights and floodlights used in professional film and television production are commonly rated at one, two, or five kilowatts, with higher kilowatt ratings generally corresponding to greater light output and the ability to illuminate larger areas or provide sufficient light intensity at greater distances from the subject. The kilowatt rating is therefore a useful practical reference when planning lighting setups, calculating power requirements, and selecting appropriate equipment for a given shooting environment.
It is important to note that kilowatt ratings describe electrical power consumption rather than light output efficiency, and different types of light source convert electrical power into visible light with varying degrees of efficiency. A one kilowatt HMI lamp, for example, produces significantly more usable light than a one kilowatt tungsten lamp consuming the same amount of power, as HMI technology converts a greater proportion of the electrical energy into visible light rather than heat. For this reason, kilowatt ratings are best understood as one of several specifications to consider alongside colour temperature, beam angle, and light output measurements when selecting and comparing professional lighting equipment.