Sorry for the delay in me responding to this question.
I don’t have a great answer for you other than to suggest looking at Pynton’s stuff here:
http://www.poynton.com/Poynton-color.html
My understanding of density is that it is logarithmic so you could think of 3 as 10^3 or 1000, etc. You probably already though of this stuff but it’s about all I have to offer… sorry
I’ll keep my eyes open for more info…
Steve