[Radiance-general] Doing manually what mkillum does...

[Lars O. Grobe]

Dear Radiance users,

I hope you all had a nice christmas and are happy playing with your 
brand-new radiance number crunchers already (time to have a look at the 
christmas peak at Mark's benchmark site again ;-) )...

I am having a question which may be basic for those here doing the 
calculation-and-formula stuff on a regular basis, but appears confusing 
to me. To simplify a model, where direct sunlight is not important and 
daylight can be considered as a hemispherical light source (uniform 
sky), I would like to do manually what mkillum does when producing a 
light modifier (not the default illum modifier). The surface to be 
modified is a horizontal flat rectangular face of, say, 1sqm. If I would 
normalize the sky source in a way that I would get a horizontal 
illuminance of, lets say, 1000 lux, ignoring obstructions, how would I 
calculate the 1 sqm light source's modifier that would replace the sky 
in my scene? Is mkillum basically calcultating an iradiance image here?

Lars.