alt Hacker NewsThe inverse-square law can be non-intuitive:
* https://en.wikipedia.org/wiki/Inverse-square_law
I know a good number of photographers can struggle with it when they're getting into flash/strobe photography (even though may be good with f-stops generally, the moving of the flash stand appropriately takes some mental 'accounting').
In your first link the narrator says he "doesn’t understand the physics of it" but there's really no physics involved (ignoring scatter). It’s just a consequence of the math. It’s relatively easy to understand if you think of it in terms of the surface of a sphere. There is a fixed amount of light coming from a point source, and as the light travels outward you can think of it as being spread over the surface of a sphere. Since the surface area of a sphere is 4pir^2, if you double the radius the area quadruples, and therefore the light intensity at any point on the sphere drops by a factor of four.
edit: And now after rtfm I see there's a nice demo of this!