Calculate works best at the sample points such as 400-700nm in 25nm increments. Spline tries to approximate the other points and fit a bell curve.
I just found out that the calculations are complex enough (and I have no resources) that this page is now invalid. but the akima spline interpolation is useful. Just try to go by your specs. The only reason I am keeping this page is because it has useful code and others have linked to it, and the hopes that someone will provide me with proper equations. But I am hearing that there is not a proper conversion between watts and mcd (millicandelas), so this MAY be a hopeless project, but I can at least try. :-) I need the help of a willing Optical Engineer.
I do not know all the variables that need to be in place. I don't mind putting them in. that's easy. but I would like to make it as easy as possible on the user - I know that not everybody knows how to calculate steradians - I know I don't remember, but I can look it up again.
This page is essentially here to do as much of the heavy lifting as possible for the user (and speed up their work so they can get their work done).
If there is someone into Optical Engineering who is willing to help me give me the equations and all the variables required to convert a generic rounded LED between mW to mcd and also from mcd to mW given at least the beam angle in degrees (such as 120°), that would be greatly appreciated! email me here! Then I can rewrite this page so everyone can use it. I know the beam angle will need to be converted to steradians.
LED mcd/W Calculator Application
how to measure the brightness of an LED properly - by Firefly Technology (hint: it's NOT lumens!)