Sunlight hours sky model method


I’m trying to understand the methodology behind sunlight hours analysis about the sky model to write a paper. I have seen some posts, but things are not clear to me, can you help me?

Which method is Sunlight Hours using for the sky model?
I digged up the source code of the component and found this variable “cumSky_radiationStudy” in def_radAnalysis. I noticed that the same definition appears in Radiation Analysis’s code, that uses component GenCumulativeSkyMtx, to generate this “cumSkyResult”. And i’ve seen that GenCumulativeSkyMtx uses gendaymtx as a function.

So, i’ve been thinking, is Sunlight Hours Analysis using the gendaymtx function of Radiance to create the sky model? Or the genCumulativeSky (Robinson) function?