You seem to understand what I was asking. The expanding universe "balloon" example was given only to describe how the distances between photons may increase with distance from the source.

"The number of photons per unit area decreases with the square of the distance from the star."

Interesting. Doesn't that also describe the diminishing effects of gravity as the distance from the mass increases? Are the two effects related?

"when observing very distant galaxies, which are nothing but points of light themselves at such enormous distances."

I don't remember seeing any photos of "point source" galaxies. I wonder at what distance a galaxy would appear like a star.

I checked on "Watts per square meter" Looks like lumens is the unit in question.

I still wonder images (light) reach us from so far without dissipating into nothing.