Luminance is that quality of a finished print that makes it seem to light up the room it's in. Yes, good topic and a lifetime to learn. I was thinking along these lines today. I bought a set of filters that are no longer made. Colored polarizers (g-y-r-bl) and I was looking at each one trying to decide what the different effects would be on B&W film. It's something that's not as easy for me as some other aspects are.