[Radiance-general] visual transmittance
Reinhart, Christoph
[email protected]
Fri, 19 Jul 2002 11:27:07 -0400
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Dear RADIANCE colleagues,
I am doing a series of rtrace daylight calculation in a room with a Southern
facade for several glazings. All glazings are "standard" so that I simply
intend to use the glass modifier to simulate them. My original thinking was
that I carry out the simulation once for a glazing with a transmittance of
80% and then I scale the results for the other glazing types, i.e.
vis transmittance 80% -> transmissivity 87% -> the rtrace calculation yields
at point 1: 100 lx
therefore:
vis transmittance 40% -> transmissivity 44% -> at point 1 illuminance= 100
lx * 44/87 = 51lux
When I tested this assumption, rtrace yielded something like 58lux for the
room with the 40% glazing. I did not expect exact correspondance but an
error of 15% is pretty substantial.
Could anybody explain to me where my error lies?
Christoph
Christoph Tito Reinhart, Dr. Ing., Dipl.-Phys., M.Sc. tel: (613) 993-9703
Research Officer
fax: (613) 954-3733
m 24 Institute for Research in Construction e-mail:
[email protected]
National Research Council Canada
http://www.nrc.ca/irc/ie/light/daysim.html
<http://www.nrc.ca/irc/ie/light/daysim.html>
Montreal Road, Ottawa Ont K1A
0R6, Canada
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<DIV><FONT face=3DArial size=3D2><SPAN class=3D945321315-19072002>Dear =
RADIANCE=20
colleagues,</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D945321315-19072002></SPAN></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D945321315-19072002>I am =
doing a series=20
of rtrace daylight calculation in a room with a Southern facade for =
several=20
glazings. All glazings are "standard" so that I simply intend to use =
the=20
<EM><STRONG>glass</STRONG></EM> modifier to simulate them. My original=20
thinking was that I carry out the simulation once for a =
glazing=20
with a transmittance of 80% and then I scale the results for the =
other=20
glazing types, i.e.</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D945321315-19072002></SPAN></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D945321315-19072002>vis =
transmittance=20
80% -> transmissivity 87% -> the rtrace calculation yields at =
point 1: 100=20
lx</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D945321315-19072002></SPAN></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D945321315-19072002>therefore:</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D945321315-19072002>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D945321315-19072002></SPAN></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D945321315-19072002>vis =
transmittance=20
40% -> transmissivity 44% -> at point 1 illuminance=3D 100 =
lx * 44/87 =3D=20
51lux</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D945321315-19072002></SPAN></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2><SPAN =
class=3D945321315-19072002>When I tested=20
this assumption, rtrace yielded something like 58lux for the room with =
the 40%=20
glazing. I did not expect exact correspondance but an error of 15% is =
pretty=20
substantial. </SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D945321315-19072002></SPAN></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D945321315-19072002>Could =
anybody=20
explain to me where my error lies?</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D945321315-19072002></SPAN></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D945321315-19072002>Christoph</SPAN></FONT></DIV></SPAN></FONT></=
DIV>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D945321315-19072002></SPAN></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2><SPAN =
class=3D945321315-19072002></SPAN></FONT><FONT=20
face=3DArial size=3D2></FONT> </DIV>
<DL>
<DD><FONT face=3DArial><FONT size=3D-2>Christoph Tito Reinhart, Dr. =
Ing.,=20
Dipl.-Phys., M.Sc. tel: (613) =
993-9703</FONT></FONT></DD>
<DD><FONT face=3DArial><FONT size=3D-2>Research=20
=
Officer  =
;  =
;  =
;  =
; =20
fax: (613) 954-3733</FONT></FONT></DD>
<DD><FONT face=3DArial><FONT size=3D-2>m 24 Institute for Research in =
=
Construction =
=20
e-mail: [email protected]</FONT></FONT></DD>
<DD><FONT face=3DArial><FONT size=3D-2>National Research Council=20
=
Canada =
=
=20
<A=20
href=3D"http://www.nrc.ca/irc/ie/light/daysim.html">http://www.nrc.ca/=
irc/ie/light/daysim.html</A></FONT></FONT></DD>
<DD><FONT face=3DArial><FONT size=3D-2>Montreal Road,=20
=
Ottawa =
=
=
=20
Ont K1A 0R6, Canada</FONT></FONT></DD></DL>
<DIV> </DIV></BODY></HTML>
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