screen equations

[Mathadon]

Direct solar irradiation is converted into diffuse solar irradiation? Does this make sense? Probably not since screens are typically perforated and therefore the light stays direct (except for diffraction).

  HShaDirTil = HDirTil*(1 - limiter.y);
  HShaSkyDifTil = HSkyDifTil*(1 - limiter.y) + HSkyDifTil*limiter.y*shaCorr + HDirTil*limiter.y*shaCorr;