[Radiance-general] Simulating light pipe performance

[Jia Hu]

Hi Lars:

Thanks for your suggestions. I search the mail archive but still have many
queries. Please see bellow, sorry for so many questions...

On Sun, Jul 24, 2011 at 3:28 AM, Lars O. Grobe <grobe at gmx.net> wrote:

> Hi Jia!
>
> I have some unfinished work on this lying around for almost one year now,
> and this topic arises again and again on this mailing list. It is true that
> the standard backwards-raytracing approach of Radiance is not suitable for
> such systems. There are several ways to simulate these if you are aware of
> what is happening, and, more important even, what kind of results you need.
>
> In general, if you do not need high angular resolution, the tools developed
> for patch-based sky models are working, and you can even calculate the BDSF
> now using the Radiance-toolchain as long as you are more interested in the
> integrated transmission then in high angular resolution. So - if you need to
> know how many hours a year you can reach a certain illuminance on a work
> plane, that should work. If you want to perform glare studies, I would
> question such results.
>

How about the accuracy of calculated illuminance? Is that accurate or
acceptable?  If I use Radiance toolchain (rtcontrib), do I have to use metal
material for tubular (round) pipe, and mirror or metal for square pipe?


> For high angular resolution, switching from backwards to forward raytracing
> is more efficient, and here the photon map extension is what we have
> available right now. Unfortunately, the development status is not really
> clear, and at least the latest available versions had some bugs that can
> heavily influence results depending on sky conditions / models.
>
The extension is developed for Radiance 3.7. It seems not updated for
several years. Is that suitable for annual simulation?


>
> One entirely different approach is to use some optical modeling tool to get
> the transmission distribution or, even easier, to get luminaire
> distributions for certain times of day / dates / weather conditions.
>

I know little about these tools. Is the optical modeling tool capable of
doing annual simulation? Could you recommend some tools? I just heart about
Photopia and only tried once.  It would be better if the tool is free, but
this does not matter.


> And then, you are free to circumvent the whole ambient calculation and try
> do keep everything in the direct calculation, which works fine with such
> setups. So for calculating horizontal irradiance, you would place a
> fisheye-type camera with a full hemisperical view on you point of interest
> looking up and integrate the radiance - as long as you reflector is
> completely specular w/o roughness.
>

Do you mean I separate direct and ambient calculations? Could you tell me
how to do direct calculation only? If I set ab =0, it underestimates the
direct sunlight illuminance. I do not know how to let the direct sunlight
enter in to the space through the tubular light pipe. What materials should
I have to use for the light pipe?

Thank you very much.

Jia
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.radiance-online.org/pipermail/radiance-general/attachments/20110724/96990ca7/attachment.html>