[Radiance-general] Radiance-general Digest, Vol 119, Issue 7

Thu Jan 9 00:46:53 PST 2014

Thank you Lars and Googs for your useful responses. Now I have a start point to tackle this :-)

> From: radiance-general-request at radiance-online.org
> Subject: Radiance-general Digest, Vol 119, Issue 7
> To: radiance-general at radiance-online.org
> Date: Wed, 8 Jan 2014 12:00:00 -0800
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> Today's Topics:
> 
>    1. Re: Using radiance for simulating light pipes (Lars O. Grobe)
>    2. Re: Using radiance for simulating light pipes (Rob Guglielmetti)
> 
> 
> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Tue, 07 Jan 2014 21:20:48 +0100
> From: "Lars O. Grobe" <grobe at gmx.net>
> To: Radiance general discussion <radiance-general at radiance-online.org>
> Subject: Re: [Radiance-general] Using radiance for simulating light
> 	pipes
> Message-ID: <52CC61A0.8030307 at gmx.net>
> Content-Type: text/plain; charset=ISO-8859-1
> 
> Hi Alejandro,
> 
> the topic of light pipes appears from time to time, and unfortunately
> the simple answer is that Radiance (and any backwards-tracer) is not
> really suiteable for the task, if
> 
> 1) you consider sunny days (you probably want to do so)
> 
> 2) you do not have a diffusor placed on the top aperture of the pipe.
> 
> There are still some promising approaches to solve the problem. One is
> using descrete patch models of the sky, such as the Tregenza scheme,
> with the direct sun contribution being distributed over larger patches.
> This implies distributing the sun radiance over a larger part of the
> sky, which smoothes out sharp peaks in the transmission - which may not
> be crucial in many cases.
> 
> The other option is using a forward extension to Radiance, such as the
> photon map. This requires a modified version of Radiance, but gives you
> a tool which has been developed with exactly applications such as light
> pipes in mind.
> 
> Finally, you may even try to generate the BSDF of a light pipe using
> genBSDF and apply this to a surface representing the bottom aperture.
> 
> The latter two options keep the resolution of the incident radiance,
> especially the "sharpness" from the sun, intact.
> 
> Cheers, Lars.
> 
> > Hi everyone,
> > I am a newcomer in the radiance community. I am involved in a project to
> > assess the light output from light pipes. We are gonna simulate the
> > light output of 2 types of light pipes and then compared them to the on
> > site measurements. I would appreciate any guiding or advise on where to
> > start the simulations. I am considering backward retracing as a more
> > suitable option than forward retracing for this particular case, what do
> > you think?
> > Thank you
> > Ale
> 
> 
> 
> 
> ------------------------------
> 
> Message: 2
> Date: Tue, 7 Jan 2014 13:45:35 -0700
> From: Rob Guglielmetti <rob.guglielmetti at gmail.com>
> To: Radiance general discussion <radiance-general at radiance-online.org>
> Subject: Re: [Radiance-general] Using radiance for simulating light
> 	pipes
> Message-ID: <826B5C1C-DC4E-410B-AA23-4D5B1716E3A5 at gmail.com>
> Content-Type: text/plain; charset=windows-1252
> 
> What Lars said, and:
> 
> Most TDD manufacturers provide performance tables based on some incident illumination on the exterior aperture, relating that flux to an expected avg illuminance inside a model space, assuming some room cavity ratio and TDD spacing. People have been known to use those tables, and an annual exterior (e.g. roof) illuminance schedule (ideally based on a weather file and Perez sky) to scale the predicted interior illuminance for an annual (or whatever) result. In this way you could use a light backwards ray tracer because you?re just solving the problem from the roof to the sky/sun. This whole process would be super fast with Lars? recommended approach to deriving the annual illuminance schedule (i.e. using gendaymtx and a single point on the roof). This approach also takes into account local obstructions (rooftop units, trees, whatever). 
> 
> Several TDD manufacturers also provide photometry files that you could use in Radiance to compute a grid of interior point illuminances, and again scale those up or down based on the roof illuminance schedule. In this way you could do a fairly reasonable accounting of an actual interior. 
> 
> The performance tables and photometry files are all a bit nebulous, based on assumptions and best/worst case scenarios, and voodoo. Your mileage may vary. Proceed with caution. Look both ways before crossing the street. But hey, it?s something. =8-)
> 
> - Googs
> 
> On Jan 7, 2014, at 1:20 PM, Lars O. Grobe <grobe at gmx.net> wrote:
> 
> > Hi Alejandro,
> > 
> > the topic of light pipes appears from time to time, and unfortunately
> > the simple answer is that Radiance (and any backwards-tracer) is not
> > really suiteable for the task, if
> > 
> > 1) you consider sunny days (you probably want to do so)
> > 
> > 2) you do not have a diffusor placed on the top aperture of the pipe.
> > 
> > There are still some promising approaches to solve the problem. One is
> > using descrete patch models of the sky, such as the Tregenza scheme,
> > with the direct sun contribution being distributed over larger patches.
> > This implies distributing the sun radiance over a larger part of the
> > sky, which smoothes out sharp peaks in the transmission - which may not
> > be crucial in many cases.
> > 
> > The other option is using a forward extension to Radiance, such as the
> > photon map. This requires a modified version of Radiance, but gives you
> > a tool which has been developed with exactly applications such as light
> > pipes in mind.
> > 
> > Finally, you may even try to generate the BSDF of a light pipe using
> > genBSDF and apply this to a surface representing the bottom aperture.
> > 
> > The latter two options keep the resolution of the incident radiance,
> > especially the "sharpness" from the sun, intact.
> > 
> > Cheers, Lars.
> > 
> >> Hi everyone,
> >> I am a newcomer in the radiance community. I am involved in a project to
> >> assess the light output from light pipes. We are gonna simulate the
> >> light output of 2 types of light pipes and then compared them to the on
> >> site measurements. I would appreciate any guiding or advise on where to
> >> start the simulations. I am considering backward retracing as a more
> >> suitable option than forward retracing for this particular case, what do
> >> you think?
> >> Thank you
> >> Ale
> > 
> > 
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> > Radiance-general at radiance-online.org
> > http://www.radiance-online.org/mailman/listinfo/radiance-general
> 
> 
> 
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> End of Radiance-general Digest, Vol 119, Issue 7
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