One thing I want remind people of is:

The inverse-square law is only valid if the source is a point.

That means for many sources it is either the wrong law (e.g. loudspeaker array¹, long neon bulbs) because of the shape or it falls apart as you go so close to the source that a significant arc-angle is covered by the source itself meaning the law is no longer accurate. E.g. if you move ever closer to a light source with some diameter, at some point the result will look more and more like an area source and less like a point source. If you move so close that your entire horizon is covered by the light source it would be absurd to apply that formula since whatever is in front of the lamp gets the light from multiple directions now.

As such it is a great and useful simplification, but knowing the limits is equally important.

¹: this array tech is is used to get a more even level falloff from the combined wavefront so you don't have to blast off the ears of the front row while being barely audible in the back.