Wattage for green screen lightning

Question

What is the minimum wattage for four-point lighting for a green screen?

I am planning to use led lights in a home studio. Is this enough?

• Key light: 300W
• Fill light: reflector
• Back light: 150W
• Light pointed towards the greenscreen: 150W

UPDATE

I think I should rephrase my question to: What settings do I need to use to get a crisp image for a greenscreen? Something like this:

I'm using four softboxes as a light source and one reflector. I was thinking in placing my subject less than 1 m away from the key light and 2 m away from the greenscreen. Something like this

I have a f1.8 lens on a Canon T3i. Do you think this would be enough?

Answer 1

Wattage has nothing to do with lumens, as different instruments provide a wide spectrum of output lumens based on lamp type. For instance, a 1.2K HMI ArriLite would put out more light than a 5000W tungsten lamp. LED, and flourescents are similar, higher output, less watts.

What is critical for greenscreen work is that you use a monitor with a simple waveform scope. When you light your greenscreen, on your waveform monitor you will see basically a horizontal line.

You want to get that line as straight and as thin as possible, at 70-72 IRE. Its fairly challenging the larger the screen (you won't be able to do this with the naked eye).

After your screen is "flat lined". Put in your on camera talent and light them for picture, using dimmers, silks, scrims etc, to cut the light.

If you do it the other way around, you will drive yourself crazy trying to get the screen at flatline 72.

This will give you the best possible key. If you have variance in your IRE (darker corners, even 5 IRE) you will have to use a looser key (meaning more edge artifacting).

I recommend for post KeyLight for AE, Lightwrap for AE.

Also, using a premium screen really makes things easier. Hollywood Rags makes an Ultra Key cloth (order by size) that is ultra bright, the material they use, therefor you need less light to get it to 72 IRE. It really pops.

Last tip most people don't know, based on your Kelvin, use the same Kelvin for ALL lamps. For your hair light; hit your talent from behind, and gel it using 1/8 magenta CTM. The magenta is complimentary to green, and will give you a clean edge, specifically on the hair.

Hope this helps!

Answer 2

TLDR: LOTS and that depends primarily on your camera, lens and size of your green screen.

A good green screen is slightly darker than middle gray. Below is a photo of mine:

To pull a good key you need to have low noise and good separation of the subject from the background (i.e. sharp edges).

So let's say you want to shoot at ISO 100 (low noise) and F5.6 (b/c sharp edges) and 1/100 shutter speed (to avoid motion blur, again sharp edges). In this case the illuminance of the green screen needs to be in thousands of lux. Let's say it's 6000 lux. Now how big is your green screen? Mine is 2m by 2m (for a static medium shot), which means 4 square meters. That means that I need 4m * 6000lx = 24000 lumens to illuminate it.

Now there is no light that will lit your green screen and nothing else, so you need some reserve. So let's say you need a total of 40k lumens (lots will be lost in diffusion or light outside of the green screen). That is about eight 1.5m 60W fluorescent tubes, which means 500W of power.

Now if you shoot with a camera that has low enough noise at 400 ISO and don't plan on moving much (so 1/50th shutter) you need 8x less light. If you get acceptable depth of field with f2.8, you'll need 4x less light again, etc. etc.