Every cameraman will have to light for green screen at some point, as keying software improves everyone is using it, even those on a low budget. Lighting for green screen is relatively straight forward, but it worth watching out for a few factors, as getting the lighting wrong on this can obviously cause serious problems in the edit. Certain situations won't show up lighting mistakes as brutally as others, for example a basic interview setup with no movement will be easier than someone with long blonde hair with some movement. The best practice is learn to light properly and stick to this setup. I'll go through the type of lights that are best for green screen shoots, but first a few basic principals.
There are loads of different ways and different lighting set ups to effectively shoot green screen, but the principals are the same.
1) Set up you green screen so it is as smooth as possible, stretch it out if need be to get rid of wrinkles, or hang it up high so the weight of the cloth pulls out wrinkles. If you are in a green screen studio, look out for any big scuffs or marks on the floor or walls. (most studios will have paint or green tape to patch up little problems)
2) Create a soft even light over the green screen (no hot spots, no shadows).
3) Light the green screen a couple of stops below your subject. Blasting the green screen with loads of light isn't a good idea, as you can bounce green light off the screen onto your subject. Lighting the screen too dark will mean that it is easier to cast shadows on the screen. The best situation is a green screen just slightly darker than the light on your subject.
4) Treat your green screen and your subject separately. Once you are happy that you have an evenly lit green screen, light your subject in the same way you normally would. Here you should be using different lights from those used to light the screen.
5) Avoid all shadows. The easiest way to do this is to create some distance between the green screen and the subject. In some cases this may be difficult, for example if you have a small room or a small green screen and the Director needs a full body shot, you will obviously be forced to have the subject near to the screen. In this case you can cut down on shadows by raising your lights and moving them out to the sides, therefore throwing the shadows down at the ground and away to the edges. Remember, all the editor needs is enough distance around the subject to cut him, her or it, out from the background.
6) Shoot at a wide aperture when possible. Having the screen out of focus helps even out any inconsistencies from wrinkles etc.
7) Use a backlight to sharpen the edges between the subject and the green screen. This should be a relatively soft light. You can use minus green gels (magenta) for this if you have them, which will cut down any green light which may have bounced onto the subject.
8) Lastly, an obvious one, make sure your talent isn't wearing any green. This also applies to reflective material, a watch or piece of jewellery, glasses etc. These could all reflect a small amount of green from the floor or walls, which will give the editor a long and boring job fixing up this issue.
There is another really important consideration with green screen: think about the finished product when lighting your scene. Normally, what you see through the lens is the finished product, but with green screen this obviously isn't the case. There is no point in creating perfect three point lighting, if the green screen setting is outside, or a night scene or a cartoon sequence etc, it will just look odd - in a real life outdoor situation where would that perfect hair light be coming from? The best way to approach this is to get as much information about the finished scene as possible. You may be given a photo or video of the plate, if not, ask questions. Will it be indoor, outdoor, sunset, night time, etc.
Types of lights for a green screen shoot.
For the green screen itself you want a soft even light. I often go with two kino flos at either side for this. It depends on how big your screen is, but 2 x 4ft 4 bank kino flos will be easily enough to cover a 12ft by 10ft screen, giving you a screen big enough for a head to toe shot of you subject. If your screen isn't as big as this, kino flo do a smaller 2ft version.
You can also use something smaller like a kino flo diva light, or you can use LED panels. I have used the Kino Celeb which is an LED panel (similar in size to the kino Diva light), and it worked well. The main thing is for the light to be soft. If you tried to light this screen with Red heads or similar you would have to move the light along way from the screen to give you a soft even light, and therefore you will end up with shadows from you subject.
I have also used space lights in studios. These lights work really well for larger spaces, they create an even light over the screen and floor and can be dimmed to work in with your subject's lighting.
This is a low quality photo from my phone, but you get the idea. This is a rehearsal and the full green screen is still being constructed. Above there are three space lights that given an even light down walls, there are a couple of defused 650s for back lights and a couple of 1ks behind large diffusion screens. The 1ks would normally create very hard shadows but bringing them far back and shining them through a large screen makes a softer light.
When you are working in a more confined space than a studio, you are going to need a smaller soft light for the subject. I find the Diva 400 is a great light for this, it has an egg create over the bulbs that helps direct the light and avoids spill on to the background. I usually use this as a key and then fill with another kino or LED panel. For the back light a 650, or a dedo light will do, I use loads of diffusion on these to soften it up as much as possible. If you are working in a studio kinos will often be mounted on the ceiling allowing you to use them as a back and others that can be used to light the screen from above.
If you are using traditional tungsten lights: fresnals, redheads or whatever, just soften them up as much as possible. Chimeras, softboxes and diffusion will all help cut down shadows. Larger diffused light sources from further away will generally create softer shadows.
Another awful photo from my phone, and the house lights are on to further confuse things, however, it shows the basic set up. The 4ft 4 bank kinos are either side of the screen there is a back light from a red head high up at the corner of the green screen, and a couple of LED panels for the subject.
Chroma Key Green Screens themselves are pretty inexpensive and you can pick up the background drapes for around 20 pounds, or 50 dollars in the USA
For the background support there are lots of options. You can use a couple of light stands, if you have them spare, attach k clamps, and then clamp on a boom pole between the poles. Another option is to buy a kit: Background Support System
Finally, if you haven't already seen them, here are two videos showing the use of green screen in multitude of films.