[Radiance-general] Using SSLD skies with sun

[Phillip Greenup]

OK - thanks for the explanation.  All clearer now!

I'm thinking that this shouldn't really cause you much problems.  You may be right that the sun will block that part of the sky nearest to the solar position, but that part of the sky that is blocked will be really small, and much less bright than the sun, so it should (I think?) make very little, to no, difference.  And because the diffuse sky is only part of the indirect calculation, a small change in directionality should again be almost unnoticeable.

BTW, you could always set the sun direction input for the SSLD definition (A8, A9, A10) equal to that generated by gensky?

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 6:53 PM
To: Radiance general discussion
Subject: Re: [Radiance-general] Using SSLD skies with sun

Hi Phillip!

> 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.

Hm, my concern was maybe a bit academic :-) For a sky with a very steep 
gradient, the sun (light) would cover the brightest spot of the sky 
(glow) - so light replaces glow. But because of the altitude 
modification gensky does for high altitudes, the sun (light) is 2.5 
degrees off the brightest spot of the sky glow - leading to light plus 
glow spot. Probably the fact that the solid angle covered by the sun is 
small, the difference is not that high, but in cases where my 
illuminance is really only due to a small circumsolar domain of the sky, 
this may lead to some higher illuminances, right? Would need some test 
models to see whether this becomes visible with a skylight. I just 
realized that I have two different sun positions in my model - the 
'real' one by the ssld background sky, and the manipulated on by gensky.

Yes, I am using you cal-file, thank you by the way :-)

Cheers

Lars.

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