Why can't they just use degrees Kelvin, and BIN emitters using that tint scale/range?
??
Because then people would understand what they meant. :p
Because you can have varying amounts of RGB and still be on the same K line. All of the labelled lines below i.e. 2500K are all the same color temp, however they have varying amount of RGB on the scale. The tint bins tell you where on the line you lie.
Any chance you can explain that graph :)