Physics in the Photo... Lighting Fall Off & the Inverse Square Law

Last night at photography class, I learned about the importance of the position of a light in portrait shooting as well as the position of people.  

Here's the video we watched:  https://youtu.be/f5BIvSBjvLg  If you're not into physics, just continue on past the first couple of minutes of the video and get into the demonstration.  

This photography class is such a game-changer for me, as it is altering my point of view regarding how I see lighting and scenery in the real world when it comes to how I want to see a finished photograph.