Citation/Derivation for Daylight CCT to xy Function

[ChthonVII]

The function for converting CCT along the daylight locus to CIE1931 xy coordinates starting on line 1647 of GradePack.avsi differs from the official equation in CIE15:2004. The comments don't explain where this function came from, how it was derived, or why it's used instead of the official equation.

It looks like the goal is to better match the underlying experimental data. Is that correct?

I can't find any other source mentioning this equation. Did you derive it yourself? Or do I just suck at google?

[Dogway]

Sorry for the delay in the response.
I did run a non-linear regression fit for the daylight and blackbody locus.
I read or maybe observed (can't remember) that the original fit wasn't too good, so I separated them into three piecewise functions.

When I get some time I can share my tests.

[ChthonVII]

Thanks! So this function gives a better match for the true value of D-something, but probably a worse match for what any given CRT manufacturer thought was the value of D-something.

I think it would be helpful for the reader if there was a comment explaining that (a) this is an alternative function that fits the experimental data better than the official function, and (b) you derived it yourself, so there's no external source to cite. That would save readers like me from chasing our tails trying to find the citation.