Quote Originally Posted by fretlessdavis View Post
It's limited by the real world application of the math.
One of my undergrad math professors used to say "The real world is a poor approximation to mathematical truth".

In Physics, theories and laws seem to be based off of perfect conditions. There is no true point light source possible-- as it would occupy no space. As mentioned before, other effects start happening with different light sources as you get really close. There is no problem with the law, but perfect conditions for it are never attained in real life.
Well said.

The inverse-square law is actually more "real-world-accurate" than a lot of physics; if you estimate light levels using it, in practice it will work impressively well. If you start dropping things off the Leaning Tower of Pisa and expecting them to fall as if there were no air resistance, or slide things around your desk and expect no friction, you see the limitations of those models pretty quickly. But to break down the inverse-square law in a practical way, you usually have to get unreasonably close to the light source---I mean, who wants to take a photo that has nothing in it but a light bulb?

Disclaimer: I'm trained as a mathematician, not a physicist; though if I'd had an undergrad minor it would have been physics.