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| Re: silly inverse square law question. |
The point of distinction in the difference is the inclusion of more (or less) light from the source being available to meet the constraints of the AI=AR to reach the entrance pupil with the varying distance based on the varying family of angles that accompany such changes. It is not because the light "falls off, iaw ISL" post reflection. It is because the angles have changed from which the object to receive/reflect the light ... adhering to the tenets of the trigonometry for vector forces involved.
I think that while we are much more in agreement now regarding the energy flux that you have referenced, my distinction is that the delta is predicated upon the change in the light falling upon the reflecting object (by the change in family of angles), rather than the radial dispersion (which remains constant) from the unchanged surface angles, post reflection.
The issue of "family of angles" is the critical aspect involved here. LS&M devotes a chapter to it, and then continues to use it throughout the remainder of the book ... striving to focus on the light that you are working with, moreover than the light you aren't, and showing how to distinguish between the two.