I just ran into what I needed to get the relationship between current and lumens/watt. I know we can definitely get it for the crees, not sure about the citizens (I still haven't looked at their spreadsheet calculator), and probably not yet for the veros as they don't have anything like the cree product characterization tool. So here's how it works, go to
http://pct.cree.com/dt/index.html and bring up a cob that you need the formula for the amps and lm/w relationship. For example, I looked into cxb 3590 CD 36V. Then you go here,
http://www.dcode.fr/lagrange-interpolating-polynomial and you go in the middle of the screen where you can list the values of x and y as pairs. I entered (1.4,172.1) (1.45,171) (1.5,169.
(1.55,168.6) (1.6,167.4) (1.65,166.1) (1.7,164.9) (1.75,163.6) (1.8,162.3) (1.85,161) which I took from the characterization tool. You click find equation and there you have it on the right. Mine came to: f(x)=−1.26984×10^7x^9+1.85397×10^8x^8−1.20171×10^9x^7+4.53884×10^9x^6−1.10085×10^10x^5+1.77806×10^10x^4−1.91249×10^10x^3+1.32096×10^10x^2−5.31647×10^9x+9.49942×10^8 which looks kinda crazy buy it should work. I did not enter all points as I didn't have the time. The more points entered the more accurate the equation will come. For cxb 3590 there are no values below 1.4A so if we have to estimate it let's say at 0.5A, we'll just use the formula and hope that the pattern of the function stays the same at lower amps. With all that being said, I think I can definitely make a Cree COB calculator that will take as an input any amperage, instead of dealing with the preset ones. It will take a good amount of time as it will be quite tedious to input all the points for all the different cree cobs and bins that are in the calculator. If anyone feels like entering all the points and extracting the formulas please feel free.
