[Radiance-general] Help - Radiance / LEED

[John Mardaljevic]

Hi Zack,

Indeed, the CIE skies can be defined by diffuse horizontal illuminance  
or zenith luminance. Both options of course available in gensky.  I'm  
not too familiar with the procedures used to estimate sky type and  
magnitude since I invariably use climate data as the basis for  
defining skies.  For what it's worth, I've long believed that there  
was a 'disconnect' between what the sky model researchers were doing  
and what end-users might actually want, i.e. a means of selecting sky  
type from basic quantities in the standardised climate files.

Even if one could claim that a particular clear sky output was  
plausible, it still seems wacky to predict for a clear sky without  
sun. I've updated my commentary on this with a graphic to show just  
how much might be missing if you don't include the sun:

http://www.iesd.dmu.ac.uk/~jm/doku.php?id=academic:daylight-compliance#daylight_leed

> BTW - the latest public review draft of LEED 2012 goes away from  
> this standard clear sky and requires the user to find the average  
> hourly values between the clearest and cloudiest days within 15days  
> of Sept 21 and Mar 21st. Someone must have been listening to your  
> concerns!

Perhaps, half-listening.  Averages for daylighting quantities can be a  
confounding notion, and often lead to contortions best left to people  
who enjoy doing this:

http://en.wikipedia.org/wiki/Twister_(game)

Do you have actual wording from the LEED draft?

Best
John

-----------------------------------------------
Dr. John Mardaljevic
Reader in Daylight Modelling
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)

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