[Radiance-general] Specular Reflections with the Daylight Coefficient Method

[Greg Ward]

Hi Kevin,

The daylight coefficient method usually puts the sun's energy into 1  
to 4 sky patches, so the rtcontrib method will work, though it won't  
give very accurate shadows.  The total energy should still be correct  
if you do it right.

Another approach is to create a set of suns at different positions in  
the sky corresponding to the expected trajectory throughout the year,  
and interpolate these results in a separate rtcontrib run.  I have  
done it both ways, and the latter technique tends to produce slightly  
more accurate shadows.  The -dr option will work properly if you do  
this to calculate reflected beam radiation.

I regret that I don't have a script to provide,  but my 2005  
presentation covers this in overview:

	http://www.radiance-online.org/radiance-workshop4/cd/website/PDF/Ward_rtcontrib.pdf

Cheers,
-Greg

> From: Kevin Thuot <kthuot at mit.edu>
> Date: June 1, 2010 6:50:05 AM PDT
>
> Hi,
> I'm trying to use the daylighting coefficient method (using  
> rtcontrib) to get annual simulation results for a room equipped with  
> a mirrored daylighting system (like a light shelf, for example). Is  
> this possible? I know that by using the -dr option, Radiance will  
> create virtual light sources to account for specular reflections of  
> direct light from the sun. However, since the daylight coefficients  
> are calculated using a blank sky having a uniform luminance  
> distribution, there is no sun for the -dr option to find. I believe  
> this would make the sky patch coefficients come out lower than they  
> should be because the specular direct reflection of the sun would  
> not be included, but my understanding of how the program works may  
> not be correct.
>
> Can the daylight coefficient method be made to work with specular  
> reflections in Radiance, or is this not possible given the way the  
> program is implemented?
>
> Thanks,
> Kevin Thuot