(no subject) Optics5 to Radiance

Hi Birger,

In the Optics5 output to Radiance the values in the glass material are
transmissivities and not transmittances.

If you take a look at the following file (made with Optics) you will see
that the glass is has a transmittance (tau) of 0.840 (in the comment) and
the definition of glass has 0.930 0.916 0.847 as R G B values. If these were
transmittances it should have been (photopic average):

0.265*tauR + 0.670*tauG + 0.065*tauB =
0.265*0.930 + 0.670*0.916 + 0.065*0.847 = 0.840 (wrong!)

but it is instead:
0.265*0.930 + 0.670*0.916 + 0.065*0.847 = 0.915 (indeed the transmissivity,
check with the formula).

So I suppose it is exporting correctly. And you can use it directly into
Radiance without converting the values.
Hope it is clear.



# FileName= Activ2.lof
# Product Name= Activ(tm) on Clear
# NFRC ID= 9936
# Manufacturer Name= Pilkington North America
# Glazing Type= Coated
# Coated Side= Front
# Transmittance= 0.840
# Front Reflectance= 0.150
# Back Reflectance= 0.148
# Thickness(mm)= 2.235
# Appearance= Clear

void glass Activ2_glass
3 0.930 0.916 0.847

void BRTDfunc Activ2_front
      0.127 0.153 0.212
      0.854 0.841 0.778
      0 0 0
9 0 0 0 0 0 0 0 0 0

void BRTDfunc Activ2_back
      0.124 0.152 0.208
      0.854 0.841 0.778
      0 0 0
9 0 0 0 0 0 0 0 0 0

-----Original Message-----
From: Birger Van den Brande [mailto:vdb_birger@hotmail.com]
Sent: 16 February 2004 15:33
To: radiance-general@radiance-online.org
Subject: [Radiance-general] (no subject)

Hi there,

just new on the list, and I'm immediatelly going to ask a question :

I'm currently working on a project concerning visual-lighting problems in
office-buildings, more specifically problems concerning blinding and glare,
so in short, visual comfort.

Now, for the glazing I'm using Optics5 to calculate the transmittance of the

used glazing-system. When I get the grafs and data (spectral), I export
this data to Radiance, via the "export to radiance" option in Optics5
itself. I then get the R, G & B values in radiance. Now, my question,
Optics5 provides transmittances and reflectances, so after exporting the
data to radiance do these values remain transmittances? The R, G & B
values, are they transmittances? So for, I haven't found any reason to
believe that the "export" function converts them to transmissivities, but I
want te be sure that the convertor doesn't comprise the trans.cal convertion


I 've got another question that is linked to the previous one. When you get

the converted data from Optics5 in Radiance, can I directly use them as
glazing-data-input in the material file for the glazing or not? At the
moment, I'm still thinking that the R G B 's are transmittances, so if I use

them directly without converting them to transmissivities, am I going to get

  realistic result? After all, Radiance uses transmissivity for the
calculation, so I'm risking to get a double-correction on my results.

If anyone can clear this out for me, I'd be very grateful.


Geschenkidee�n en e-cards voor Valentijn ! http://www.msn.be/valentijn

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