[Radiance-general] GENBSDF of a light pipe

Mon Jul 14 05:27:15 PDT 2014

Just a hint here, this is the way I would try; even if I have not ever
worked with this kind of device.

1.- The diffuser, my guess, can be modelled with a Transdata material
(see Radiance
Reference Manual <http://radsite.lbl.gov/radiance/refer/refman.pdf>). Just
one surface on the top of the cylinder with the proper material.

     "Plasdata is used for arbitrary BRDFs that are most conveniently given
as interpolated data. The arguments to this material are the data file and
coordinate index functions, as well as function to optionally modify the
data values...
      ... Transdata is like plasdata but the specification includes
transmittance as well as reflectance"

2.- I would include the diffuser on the input to genBSDF. Also, you should
be careful on specifying the Thickness of the device (i.e. length of the
pipe + diffusers).

3.- I cannot really help you. My guess is that you will have only a few
elements (diffuser on top, cylinder, diffuser on bottom... anything else?)
so this calculation might be pretty efficient. I would just choose some
pretty "high" parameters.

Lets see what the Gurus say. But this would be my initial guess.

Best!

German

2014-07-14 5:21 GMT-04:00 Alejandro Pacheco Diéguez <paxeco2205 at hotmail.com>
:

> Hi all,
> Thanks for the answer to my previous question. I have some more questions
> regarding the steps to generate the BSDF representation of a light pipe
> using GENBSDF. I will be using this BSDF in a 3-phase-method to assess the
> light pipe performance.
> My light pipe consists of a straight vertical cylinder made of a highly
> reflective material with a clear glass pane on top (collector) and a
> diffusing glass at the bottom (diffuser). I have a BSDF of the diffuser
> provided by the manufacturer which I would like to include. This
> description consists on a series of files for different incident angles
> every 10 degrees. Below is an excerpt of the first of these files for an
> incident angle of 0 degrees:
>
> #pgII DSF data read from database by pab Ltd "mountain"
> #see http://bsdf.pab.eu for pgII gonio-photometer and BSDF details
> #mountain-version "pab mountain V2.9.1"
> #database-host pgdb
> #database-name pabpg
> #measured_at "2014-01-18 12:34:22"
> #data_read_from_db "2014-01-30 21:26:23"
> #database_id 5383
> #datapoints_in_db 259193
> #database_reference_id 5379
> #integrated_value 0.75 6.3
> #sample_label "ZTC014_0001"
> #sample_name "Velux_ZTC014_0001"
> #lamp "halogen1"
> #beamshape "inf,f=300,a=1"
> #filterlamp "IRcutoff"
> #filterdet "BG18,25mm"
> #comment "velux dataset1"
> #mcomment "$Id: do_meas_batch.c,v 1.33 2013/01/05 13:54:16 apian Exp
> apian $|daq serial[0]="007 " (channel
> minimum)|optfile=fullrot-30_broadT_50|userdata=$Header:
> /usr/local/pab_pg/etc/RCS/userdata.luna,v 1.22 2013/09/17 07:22:27 pgadmin
> Exp pgadmin
> $|cxtcounter=yes|bl_armB=0.0075|daq_ss=100|speedbend=(0.03,0.015)|lamp_cycles=155
> poweron=34655 [h] last_change=164 [min]"
> #column daq
> #dump-host sun1
> #incident_angle 0 0
> #intheta 0
> #inphi 0
> #rear_integral 0.751
> #mountain_minimum_angle 0.1 [deg]
> #datapoints_in_file 115477
> #format: theta phi DSF
> 90.04250 -100.19987 6.031e-04
> 90.23273 -100.16634 4.376e-04
> 90.43701 -100.12965 4.245e-04
> 90.62713 -100.09495 4.482e-04
> (...)
>
> My questions are:
> 1. How to include this diffuser BSDF as a Radiance material?
> 2. Should I include the diffuser BSDF in the model that I will use to
> generate the BSDF of the whole light pipe? An alternative I can think of
> would be not to include it and then juxtapose both BSDFs as two parallel
> diffusers. Would both these options work well?
> 3. Lastly, I am a bit lost with the rtcontrib settings when using GENBSDF
> for this particular case, some help here would be much appreciated.
>
> Thank you in advance.
> Ale
>
>
>
>
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>
>

-- 
*Germán Molina L.*
Ingeniero Trainee
Hunter Douglas Chile S.A.
Celular +569 89224445

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