Interesting dialogue on this subject. I also do not understand why one would measure the step wedge density in UV mode. The only time that this would appear to be a valid consideration would be when the step wedge exposure on film would be facilitated by UV light.

The step wedge density would seem to be valid when measured by the densitometer channel most closely approximating the spectral qualities of the light that would be exposing the step wedge onto film.

What am I missing here?