Quote Originally Posted by marko View Post
I think I can help.
In general a lighting ratio refers to how strong the main light (key) is in relation to the fill light and other lights. Here's an easy example:

You have a model sitting on a chair and the main light (8 feet away) is at her right so she is being sidelit.
-The right side is getting 1 'unit' of light.
-Then you have a fill light lets say it's right behind the camera and shining at the model again 8 feet away. The fill and main light are putting out the same amount of light.
-The fill light hits both the right side and the left side.
- So the right side is getting 2 units of light and the left side only one unit.
-This is a 2:1 ratio

In order to measure this precisely for consistent results, you can use a light meter to measure the lights individually.
Hope that makes sense.
Thx
Marko
well done, Marko! thanks for taking the time to do that !