"Let's say we have a scene with a wall and two lights. One light is twice as far from the wall as the other. The intensity of illumination at the wall from the furthest light will be exactly half that of the other, whether you place the lights 1 foot and 2 feet from the wall or 1 and 2 metres."

Now that I understand. You and BB should collaborate on a book/tutorials. Between the two of you, you'd reach the widest audience. IMO, people who don't get the numbers at first would be more likely to come back to them if they at least get the basic concept. Not that BB's explanation lacked the essentials, just that hitting the equations may cause cerebral gimbal lock in the math challenged as I are one. e.g. Once I've snapped to the whole breasts larger concept, I'll probably get to understanding the cup size formula at some point - or something like that. And darn, I used to know that formula too, creeping senecence.

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken