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Video lighting basics – understanding electricity

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John DeMaio on July 24, 2011 - 10:16 pm in Featured, Intern Basics - Start Here, Lighting and Grip

Lighting is what separates the men from the boys when it comes to video and film production. Understanding lighting and using it properly is a talent that takes time to learn.

As we make our way down this path we will all experience different instruments that will help us turn our darkened scene into a work of art. Some will get to use expensive production lights. Some will create their own DIY lighting kits and some will try to use everyday objects like lamps or work lights. These are all acceptable, because they are all tools to help you create. However, the most common mistake that all beginners make when first learning how to light for video of film has nothing to do with the type of instrument used. It has to do with understanding how those instruments work. So today, we’re going to discuss the basics of electricity so that I can do my part to help keep you from blowing a circuit on your first shoot…or worse…getting yourself electrocuted on your first job.

Alternating Current and Direct Current

You can either use a battery to power a device or you can plug the device into an electrical outlet. When you’re using batteries you are using direct current to power that instrument. Typically you would find batteries on cameras, audio mixers, microphones and perhaps even video monitors. In a Direct current situation the direction of the flow of electricity is in one direction.

Direct Current model - current flows in one direction

Since I’m talking about lighting for most of this post, I’m going to focus on Alternating Current. We’ll get to Direct Current  and batteries later.

When you need to plug an instrument into the wall, you are dealing with Alternating Current. Alternating Current devices work much like all the other devices that you plug into the wall at home; toasters, televisions, coffee makers, etc. Alternating current moves in two directions; it periodically alternates directions in a cycle. This happens because a generator at a power plant somewhere is spinning a large magnet around a coil – creating electric current. Without getting too technical, as the magnet changes directions (spins) the poles of the magnet (north and south) alternate, thereby changing the direction of the current. If you would like a more in-depth explanation please visit our friends at How Stuff Works.

Alternating Current model - current cycles or changes direction

In the United States, we use Alternating Current (AC) to power our homes and offices. On set, we use AC to power our lights.  Now I know what you’re thinking…”I can plug my camera or audio equipment into the wall and also use a battery.” This is true. However, take a look at the thing that you’re using to plug that device into the wall. It usually has a large box attached to it. This converts the AC from the wall into DC that the camera or audio mixer can use. But nice try…

Watts, Volts, Amps, Ohms and Current

You have probably heard about Wattage before, especially if you ever replaced a light bulb…and Voltage might also ring a bell. Amperage and Ohms may be a little less common, although if you had eighth grade science you should have some idea of what I’m talking about. There is a great analogy that explains this a bit better.

Imagine a pipe with flowing water. The voltage is equivalent to the water pressure, the current (measured in Amps) is equivalent to the flow rate, and the resistance (measured in Ohms) is like the pipe size. Now imagine aiming that pipe at something like a water wheel. The water wheel represents the energy created (measured in Watts.)

Water pipe analogy for understanding electricity

You can increase the power generated by the waterwheel in two ways.

  1. You can increase the pressure of the water coming out of the hose (Volts) and it hits the water wheel with more force turning the wheel faster and generating more power.
  2. You can increase the flow rate (Amps) and the waterwheel turns faster because of the weight of the extra water hitting it.

To calculate the Wattage for a given device, you would simply multiply the Voltage and the Amperage. You could also figure out the Amperage by dividing the Wattage and the Voltage. This second equation is more important to us. In our little world of production we typically know the Wattage of the light (it’s usually how we name them) and we also happen to know the Voltage (it’s either 120 Volts or 240 Volts) – this is usually printed on the instrument or can be determined by the type of plug used. If the plug looks like something that you could plug into the wall of your house, it’s 120 Volts. Let’s put this into practical terms:

Arri 1000 Watt Fresnel or "1K"

An Arri 1K is 1000 Watts and uses 120 Volts. Using the equation above, 1000 divided by 120 = 8.3 Amps

This would give you an idea of how much energy you are consuming, but how does this help on set? Good question. Let’s take a look at how this applies to our industry.

Real world electricity

The only way to understand how all of this works would be to show you how it will all go wrong. So let’s come up with a typical scenario.

You are called to do a shoot at a doctor’s office. It’s a simple interview set-up, but the producer wants to make it “look pretty.” The doctor’s office is in an older part of town and it’s rather small – four exam rooms, a back office, a reception area and a small kitchen area. You have an Arri kit with you that has two 1K’s (1000 watts each) a 650 (650 watts) and a 300 (300 watts) and you don’t have any dimmers so you have to run everything at full blast. Luckily, you have a ton of scrims and diffusion so you can make it work.

The producer wants a high-key lighting situation, but she also wants you to “do something with that background…maybe find a plant somewhere…that would look nice.”

You begin with the 1k for the key light, followed by the 650 for some fill – diffusion and scrims on both. Then you put the 300 in the back for a nice little hair light. Next is that pesky background. You find a plant in the other room and move it into place. Then you take the other 1K and start lighting the wall and the plant. You’re getting nice and creative by putting a little pattern on the wall but also hitting the plant just right.

Just when you’re happy with your work, you hear a loud “POP” sound. All of your lights go off…followed by all of the computers in the building. Computers that had serious medical information that wasn’t saved. Many people have now entered your room and they’re all yelling at you, including the producer that was angry with you already – like most producers. So now what?

Well, you obviously popped a breaker. It’s an easy fix as long as you can find the circuit breaker. However, getting that medical information back (that wasn’t properly saved) is not going to be an easy thing to overcome. So let’s take a look at what you can do to fix this problem in the future.

How many Amps in a circuit?

The reason that you popped a breaker in the example above is directly related to the amount of Amps that you were drawing in the circuit in that room. In a typical small office/ home setting, you are looking at a total of 100 – 150 Amps for the entire home or office. Some older buildings may even be lower than that. On any given circuit, you will have between 15 and 20 Amps. There are larger capacity circuits, but these are usually put in place for larger appliances like stoves or clothes dryers.

You have to assume that every circuit that you plug in to is a 15 Amp circuit. Unless you see this:

20 Amp outlet - notice the "T" shape

this type of plug denotes a 20 Amp circuit. You can always tell because the slot on the top left looks like a “T” – “T” for “Twenty.”  (Not really, but it’s a good way to remember.) It is always a safe bet, however, to assume every circuit that you plug into is 15 Amps – this will save you a ton of headaches.

Now if only there was some way to figure out how many Amps your light kit consumes….then you would be able to see how many lights would work safely on a circuit without overloading them….

Now put it all together

You know how electricity works now. You know the simple equation for calculating Amperage and you now understand how offices/homes are wired. So let’s put the whole thing together and figure out this lighting situation…again.

  1. If the building is old, look for the circuit breaker. This isn’t always easy or possible to do but it is a good first step to figuring out your lighting situation. It’s a good idea to do this no matter how old the building is – but I understand being rushed by the producer. The best thing about finding a circuit breaker is that you can usually see how the circuits are broken up in the home/office. It will also tell you how many total Amps.
  2. Once you settle on a shooting location, check the electrical outlets for signs of a 20 amp circuit - remember the “T” on the outlet. Twenty Amp circuits give you more room and will make your lighting troubles much less.
  3. Lay out your lights and use the calculation above to check your Amperage. In the example above we know that the 1K is about 9 Amps, the 650 is about 6 Amps and the 300 is about 3 Amps. Combined, they would equal about 27 Amps – well above a single circuit. So you have to figure out how to divide your lights into three separate circuits – one for each 1K and one for the 650 and 300. That would give you 9 Amps for the 1K, 9 Amps for the other 1K and 9 Amps for the 650 and 300. (6+3=9)
  4. Run extensions for each of the 1K’s into separate rooms. You can keep the 650 and the 300 together on the same circuit in the room but make sure that each 1K has its own circuit. This will give you enough separation and will spread out the amperage of your kit nicely. Try to get as much separation as possible and look for obvious breaks in the circuits. In the example above I mentioned a kitchen area – this is a good place to go because it would usually be separated from other rooms.
  5. Tape down your extension runs – especially across doorways. Make sure you tape them down properly!

Most of the time, you will have more than enough electricity to work with on location. Typically different offices will be on different circuits so it is usually a good idea to run at least one of your lights into an adjacent office. It is always better to be safe when it comes to electricity. Calculate the amount of Amps that you are using and make sure that you don’t overload the circuit. Also, remember that 15 Amps is a powerful jolt. It won’t kill you (typically) but it will sure sting quite a bit!

Photo: zigazou76

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