As noted before, the inverse square law applied to point sources, not collimated sources nor extended sources. Those follow other laws. I do not have an optics book handy so that I can concisely state these laws, but if the rays of light are collimated [parallel, example sun light] or from extended sources [also large defuse sources, again sun light with atmospheric scattering] light does not fall of as the square of the distance from the source.

Steve