[Radiance-general] Approximating the gross daylight flux thro ugh venetian blinds.

[Reinhart, Christoph]

Greg, I think that it would be REALLY useful for daylight-coefficient-based
daylight simulations if someone (meaning you:)) came up with a BRTDFunc for
blinds. This way one could simulate interior annual illuminance profiles
with the blinds opened and closed. This is already possible if one simulates
the blinds geometrically in gory detail (genblind), but the simulation times
are horrendous. I assume the calculation time penalty would be less severe
if one used "BRTDFunc" instead? To my knowledge, mkillum cannot  be used
with a daylight coefficient approach since mkillum is tied to a specific sky
condition? 

Christoph

-----Original Message-----
From: radiance-general-bounces at radiance-online.org
[mailto:radiance-general-bounces at radiance-online.org] On Behalf Of Greg Ward
Sent: Thursday, October 28, 2004 11:28 PM
To: Radiance general discussion
Subject: Re: [Radiance-general] Approximating the gross daylight flux
through venetian blinds.

I gave it a little more thought, and I'm note sure how useful it would be to
have a BRTDfunc that approximates the aggregate behavior of venetian blinds.
The only context where this might prove useful is in performing daylight
analyses where you don't care about external reflections and the users
doesn't care to visualize the space.  Because a BRTDfunc doesn't include the
directional-diffuse portion in its indirect component, it wouldn't get an
accurate contribution from light reflected off external surfaces.  The best
it could do is get a reasonable value for the indirect solar due to light
hitting the blinds directly.  Mathematically, even this would be difficult
-- I'm guessing it would take me a day or two  to work up a reasonable
approximation.  
As far as the appearance goes, one would see a semi-translucent material if
one was to visualize your model with this material, which wouldn't end up
looking like blinds at all.

In summary, I don't think this would be much of an improvement over a
mkillum solution.  Does anyone else have some thoughts on this?

-Greg


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