The following two low-budget, crude green screen lighting setups differ in the positioning of the screen lights relative to the talent. Which is better?
1) Screen lights further away from the screen than the talent:
2) Screen lights equidistant with the talent from the screen:
Well the 2nd is better. But the correct way is to light your Green Screen first, and you want to have it lit so it's a flat 70 IRE. You'll need a monitor with a Waveform option, and the waveform should pretty much be a flat and very thin line at 70 IRE.
You can't do that visually (eyeballing).
Then you place your talent so that they are separated as much from the BG as possible, casting no shadows onto it.
Light you talent with the same color temperature light as the green screen.
Hitting your talent with a hairlight that is gelled 1/4 magenta will help reduce edge issues.
As well as avoiding shadows, another reason you want to get the green screen as far away behind the talent as possible is to avoid any green spill. (that is, green color cast light being reflected off the green screen and hitting the talent)
Neither are great options, you should have an extra light on the subject and side light with an overhead fill (third light).
