[Radiance-general] Using SSLD skies with sun

[Phillip Greenup]

Hi Lars,

The SSLD sky generator creates a diffuse sky distribution.  If you don't put a sun in there, there won't be one.  If you're sky model involves a diffuse sky that is brightest in the sun direction, but the sun itself is not directly visible, then you'll just need to ensure you get the diffuse horizontal illuminance you're looking for (and that's the hard part - what should the diffuse horizontal illuminance be?).

So you won't end up with two sun definitions.  And you control the diffuse and direct components of global horizontal illuminance.  If the sun is not visible, it shouldn't be in the model, the direct illuminance component will be zero and the global will equal the diffuse illuminance.

This is assuming you are using my old SSLD sky generator / cal file.  Could be a different story if you're using something else?

Cheers,
Phil.


-----Original Message-----
From: radiance-general-bounces at radiance-online.org [mailto:radiance-general-bounces at radiance-online.org] On Behalf Of Lars O. Grobe
Sent: Wednesday, 12 August 2009 6:13 PM
To: Radiance general discussion
Subject: [Radiance-general] Using SSLD skies with sun

Hi,

I know that not many here use the SSLD skies, but maybe one or another 
has a comment on it...

I am currently using gensky to find the brightness levels and sun 
position required to use the SSLD skies. Now I am wondering whether this 
combination hides some risks.

First, when I add a gensky-sun to the ssld-sky, in my understanding this 
should not change the horizontal illuminance but be kind of a technical 
optimization, replacing the bright glow spot where the sun is seen by a 
source of type light, thus making sure that shadow-test actually hit it. 
This would require the flux of the sky (glow) part to be covered to be 
the same as the flux of the sun light source.

Second, gensky manipulates the sun position when coming close to the 
zenith and sets it to 87.5 altitude. I am in a tropical country, where 
this 90 degrees can be reached. In such a case, I would have two suns in 
my sky definition - the one in the ssld glow source (at 90 degree) PLUS 
the gensky light source at 87.5 degree, right?

I am just trying to debug my sky setups, so any comments are appreciated :-D

Cheers Lars.

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