This is an absolutely fundamental concept and is important to development as a filmmaker. It's a really simple pice of shorthand that cinematographers and gaffers use to keep track of lighting setups across different shooting days. It's called a lighting ratio or a contrast ratio.
Mike from the SubStream's "Film Lab" has some tips regarding film lighting.
Grab your light meter, because here comes Professor Mike's lesson on lighting ratios, a concept that's easier to understand than you might think. Impress the technicians on your next film shoot.
This is film school condensed and packaged for your mass consumption. Learn the insider's tricks to making movies!!!