[Radiance-general] Re: Calculating maximum illuminance levels from daylight

[John Mardaljevic]

Ben,

> So, I am still unsure weather Radiance or Gensky will automatically 
> calculate the direct and diffuse illuminance given a clear sky, time 
> location etc. and if it does will these numbers be realistic or 
> theoretical?

Yes, gensky can *estimate* absolute values from just location, time
and user specified sky conditions, e.g. CIE clear.  But there is no
knowing how good the estimate is until you make comparison with
absolute values from, say, a TRY.  My suggestion is: find the
maximum global horizontal irradiance (& associated diffuse horizontal)
in the TRY, and use those to set your -R and -B gensky parameters.
Doesn't matter too much when in the year it occurs, it's more a
case of getting an idea of what likely magnitudes are.
Maybe increase the overall value by a little to account for very extreme
conditions, but be careful not to exceed theoretical limits.

-John

-----------------------------------------------
Dr. John Mardaljevic                     
Senior Research Fellow
Institute of Energy and Sustainable Development
De Montfort University
The Gateway
Leicester
LE1 9BH, UK
+44 (0) 116 257 7972   
+44 (0) 116 257 7981 (fax)

http://www.iesd.dmu.ac.uk/~jm