I've done a lot of greenscreening before but always in well lit environments. I want to greenscreen some shots of someone exploring a cave so it should be relatively dark. My concern is when lighting the greenscreen if I throw a couple lights on it for even lighting I suspect some of that light will be reflected back onto the actor who will have much less light on their face. I am assuming the best way to do this will be to light the green screen with lights hooked up to dimmers then after lighting the talent dim down the green screen lights so that they don't light up his back. But thought I'd run this by everyone in case someone has experience with this.

If you place the talent far enough away from the screen, there shouldn't be any spill. I'd recommend moving the talent out from the screen as far as you possibly can.

If you try to dim the lighting on the screen too much, you'll basically have a darker shade of green, which will not key out anywhere near as well as a bright one would. You want a green screen to be as brightly lit as possible, because the reason green is used in chroma key in the first place is that bright green has a very high luma value, which makes it easier to key out.

Also, keep in mind that you don't necessarily need to use only a small amount of light on the subject as if he or she is in a cave--you can in fact light him or her very brightly if necessary and then reduce gamma in post. If the light source in your cave footage is soft and not directional, you can light the subject very evenly. If there's a directional light source in the cave footage, then light the subject with a hard light with the same general light perpsective.

Thanks. I was going to shoot the talent about 6 feet from the screen but I can probably move him a little further away. What worried me about lighting him brighter and changing it in post was the fact that he will be carrying a red glowing orb and the brighter lights would diffuse out the red glow. I'll play around a little with this. Thanks again.

Shoot bright, then turn down the contrast/gamma/brightness as needed in post. If you shoot too dark, not only will you get more spill from the brightly lit screen, you will get more noise.

The main thing is to achieve the relative lighting that you want. Are you going for diffuse light, or a hard source with high contrast? The main thing is to keep the faces reasonably well lit. (Assuming that the story doesn't call for them to be hidden in the shadows.)

You could also try one of those light-ring keying systems - do a search under reflecmedia chromaflex - the only problem is finding someone who will hire one out

"...he will be carrying a red glowing orb and the brighter lights would diffuse out the red glow."

You could supplement the red glow with a red light just off camera that shines at his face. The audience will mostly be looking at his face, so that is what really needs to show the glow. However method you are using to make the orb glow, you could also try cranking up it's output. There are some super-bright red LED lights out there. Rig it so that most of the light goes back at the actor so the orb itself does not go beyond 100ire and turn white to the camera.

One approach would be to use a blue gel on your overall lighting with a red gel on the spot for your lead actor.

Blue cuts out a lot of light and makes faces look colorless. It also gives a feeling of natural or moon light as compared to artificial light.

A red gel lets a lot of light through and will easily swamp a blue gelled light - especially on a face.

The end result will get enough light to the camera to keep it out of the noise, and will still emphasize the red lamp and lead actor. Best of all, it should key nicely over green.

Thanks for the feedback. I'll play around with some of those techniques.