The math of placing lights for greenscreen

[Mathew Rudenberg]

So, I'm lighting a 40x20 greenscreen coved into a 20 foot floor, and I'm looking for thoughts/suggestions.

 

The stage doesn't have a cyc so I'm hanging a 40x20 rag, coving it at the bottom (18' high ceilings) and painting 20x40' of floor. (open to suggestions on this rig but that's more a question for grip)

 

The plan is for it to be a standing and lit greenscreen to visit over a 3 week shoot.

 

First question is digi vs chroma green. I lean chroma because there's less bounce back from the floor, and since chroma is darker it tends to naturally read at a stop under key (which i believe is optimal for keying) and I believe chroma is more common painted on built in cycs. However I am curious if any of you find it harder to key since the color is less saturated?

 

Then there is light selection and placement.

 

Super green kinos are nice, but I imagine problematic if the light falls on the actors. Also I don't want there to be a difference between the back wall and the floor. So I'm leaning towards a row of spacelight (prob 2k)

 

I should mention I'm shooting on the c300 - so the native iso is 850.

 

The primary question I have is:

 

Is there an easy way to calculate the spacing between the spacelights, as well as the height/distance from the wall and the floor?

 

If I place them 16 feet up and 16 feet from the wall, what math I remember tells me they will be 22 feet away from the cove, which drops the intensity by more then a stop - do I have to fill in the cove with additional units?

 

Thanks in advance!