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Using the Power Equation in Video Production

written by: Shane Burley•edited by: Rhonda Callow•updated: 7/7/2011

Learn how to employ the power equation so you can figure exactly where and how you can plug in lights for filming on location.

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    Digital Video Lighting

    Lighting is the most fundamental aspect of composing a moving image. This was true during the development of motion pictures because of the way that sensitive film stock would interpret images. This became even more crucial when video came into play and did not have the depth of field and resolution of the 16mm and 35mm film stock of the past. High Definition has made waves to make image quality better for even passive framing, but for real film work you are going to have to go back to planned and plotted lighting set ups to make your images really work. To do this light kits and lighting equipment is essential, but for on site locations that are not in some special studio the power that is needed can be difficult to come by. Most locations are difficult for this, and if you are outside it is next to impossible. Lights for film and video production do not run on small amounts of power and they require a substantial amount. To make this happen you have to negotiate with what you have available to you on your source and try to distribute the lights plugs around so as to minimize the possibility of a short or other malfunction. The best way to do this is to utilize the power equation.

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    Watts, Amps, Voltage and Lighting

    Your lights will likely be measured in wattage, which is the total power that is being outputted. The amount of wattage also relates to the overall brightness of the bulb that you are using and style of light. This is why, logically, a 1K watt Tungsten bulb is going to be much more powerful than a 200 watt one. Voltage, technically referred to as the "potential difference" is a measurement of the overall force that electrical current has. Amps measure the overall current that is coming in, or what is really the "volume of electricity" per unit of time measurement.

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    Power Equation

    The power equation is designed to help you algebraically find out the missing bit of electrical information for a circuit if you only have part of it. The base incarnation of the power equation is:

    Watts = Volts X Amps

    This will also alternatively work as:

    Amps = Watts/Volts or Volts = Watts/Amps

    This fairly basic equation will answer a lot of questions for you as to exactly how much power you have the ability to pull from a given location. The Gaffer, who runs the electrical circuitry of the filming location, will immediately ask to go to the circuit breaker when scouting a location. You are going to have to determine what is available and how much you want to pull from your available circuits. To do this you gain the available information you have from the circuit breaker or any other information to essentially fill in the algebraic blanks. For example, if you can find exactly what the amps and voltage that is available you will be able to determine the amount of watts that you can use. To make this useful you then have to determine what types of lights you can use and how you can spread them out into different rooms. It is best to enter into the situation with a basic idea of the wattage you would like to use so you can then begin to eliminate things as the limitations of the circuit become apparent through the power equation. Make a list of the different places that you can find outlets and then add up the basic amount of wattage that is available. You can then see if this matches your original number or if it needs to be fundamentally changed.