Inverse Square Law is a key technique to use and understand when shooting with light – so always. Understanding Inverse Square Law allows for quick acting upon exposure changes within a shoot.
Inverse Square Law basically means when the distance from the point source is doubled a 1/4 of the light is illuminated.
e.g- point source is 5Ft away from subject at F11 – move subject 10ft away from point source at 5 F5.6 (move 2 Fstops) will mean level of exposure is the same.
Point Source = Light