<br><div class="gmail_quote"><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div class="im">
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</div><span style="color: rgb(102, 51, 102);">I would go with this definition. But the reflections here are those that</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
happen between two parallel interfaces of a refracting material as the</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
front and back of a sheet of float glass. Some light is reflected at</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
the back of the sheet when the light exits the glass. This light will</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
travel back through the glass to the front and again a small amount</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
will be reflected towards the back and so on.</span><br>
<br></blockquote><div>I know what you mean but i am sitill confused the difference between Transmisivity and Transmittance? <br><br>What is the difference between the first three parameters and trans (the second to last parameter) in trans definition?<br>
<br><br></div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<span style="color: rgb(102, 51, 102);">The formula to calculate transmissivity from the transmittance of glass</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
(VLT) takes these inter-reflections into account and so you can model</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
the two interfaces of a single pane of float glass with one single polygon</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
in Radiance and you don't have to calculate the reflections during the</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
ray tracing process.</span><br style="color: rgb(102, 51, 102);">
<div style="color: rgb(102, 51, 102);" class="im"><br>
> According to Andrew's email, for glass with VLT of 0.325<br>
> has a transmisivity of 0.354. The glass is defined as<br>
><br>
> void glass glazing.325<br>
> 0<br>
> 0<br>
> 3 0.354 0.354 0.354<br>
><br>
> For trans with VLT 0.325 and no diffse transmission.<br>
> Can we difine it as the following?<br>
><br>
> void trans window.0.325<br>
><br>
> 7 0.325 0.325 0.325 0 0 1 1<br>
<br>
</div><span style="color: rgb(102, 51, 102);">The correct definition would be</span><br style="color: rgb(102, 51, 102);">
<div style="color: rgb(102, 51, 102);" class="im">void trans window.0.325<br>
</div><span style="color: rgb(102, 51, 102);">0</span><br style="color: rgb(102, 51, 102);">
<div style="color: rgb(102, 51, 102);" class="im">0<br>
7 0.325 0.325 0.325 0 0 1 1<br>
<br>
</div><span style="color: rgb(102, 51, 102);">This produces a dark clear material without any specularity that has</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
a VTL of 0.325 (or nearly as far as I can tell from my tests). But it</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
is not the same as glass.</span><br style="color: rgb(102, 51, 102);">
<div style="color: rgb(102, 51, 102);" class="im"><br>
> For glass, the light transmitted would be specular transmitted,<br>
> is it right? If right, what is the differrence between above meteirals<br>
> definition - glass glazing.325 and trans window.0.325?<br>
<br>
</div><span style="color: rgb(102, 51, 102);">The most obvious one is that "glass" is a specialised "dielectric"</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
material type which modulates the reflection according to the</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
angle and refraction index of the material. So if you want to</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
reflections/refractions of glass with another material you should</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
start with "dielectric" not "trans"</span><br style="color: rgb(102, 51, 102);">
<br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
The "window.0.325" material defined above has not specularity</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
and no roughness. The glass material has a visible specularity.</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
Just create a small test scene with a bubble of glass/trans and</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
a light source (like the sun) and you will see the difference.</span><br style="color: rgb(102, 51, 102);">
<br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
If you don't care about the particular refraction of glass and</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
specular refraction and only focus on VTL you could say the</span><br style="color: rgb(102, 51, 102);"><span style="color: rgb(102, 51, 102);">
materials are similar or equal depending on your use.</span><br>
<br></blockquote><div>Actually i run the simulations by two different materials i found the illuminance in the room is a little different. Why is it different?<br><br> For "dielectric" definition, is anyone can tell me where i can find the detailed definition and the instruction fo corresponding parameters?<br>
<br>Best Regards!<br></div></div><br>