[Radiance-general] Questions about uniform sky

[Christopher Kings-Lynne]

> I'm just trying to understand a few things about using a uniform sky.
> 
> 1. With a uniform sky, how can I determine the theoretical irradiance or 
> illuminance at 0,0,0 looking straight up?  I'm currently testing a 
> polygon on the z=0 plane and I get a slight variance in the illumination 
> across that surface, due to slight errors in the calcs I presume.  What 
> I need is the theoretical exact value...

OK I presume I have to convert this brightness value:

# Ground ambient level: 23.8

Into an illuminance value.  Ummm, what is "brightness" as far as 
Radiance is concerned and how to convert to illuminance?

> 2. With a uniform sky, will the position of my test plane matter?  ie. 
> If I translate the plane from the origin +10000 in the Z direction, will 
> the illumination on that plane still be identical?

OK, I tested it and I can easily go up many tens of kilometres and still 
have same illumination...

Chris