Hi all,
genssky needs global horizontal illuminance and global horizontal illuminance as its inputs. Yet in most station data, only irradiance values are available. There are several luminous efficacy ratios one can assume, though; some are listed in color.h.
What is the correct efficacy ratio to calculate the illuminance values fromdiffuse horizontal irradianceand direct normal irradiance for genssky / gendaymtx?
Hi Nima,
It’s a good question, and deserves a better answer than this, but I’m not sure the efficacy conversions are applied in the most proper way in genssky. It is at least consistent in always using 179 lumens/watt, so this is what I would recommend for your conversion. It gets divided out again in the code, so ends up being a no-op if you use this value.
Best,
-Greg
Since your irradiance data is in solar spectral range, you need to convert to illuminance using the Perez luminous efficacy model (1990) used in gendaylit and gendaymtx. gendaylit and gendaymtx internally does this conversion.