translucent glass

Hello Everybody,
I am now modelling my skylight case, a 36' x30' room
with four 4' x 4' skylights distributed evenly.(well
depth 3'). In my Doe 2 model I am using a flat glass
which has properties similar to that of a
2 dome fiberglass(translucent) with Visible
transmittance = 0.5, SC = 0.45
I need to create a similar glass type in Radiance.
I am using the trans material type and based a on
previous discussion have created

void trans skylight
0
0
7 0.54 0.54 0.54 0 0 1 0

Is this the correct material definition.
What would be the definition for a similar white
translucent material.(Would the color effect the
illuminance values inside)

Also I know that I need to use mkillum for this.Do I
need to define both the window surface as well as a
polygon below the well as illums or simply the polygon
below the well so as to obtain accurate results.
Please Guide me with this.

Thank You
Arvinder

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Hi Arvinder,

From: Arvinder Dang <[email protected]>
Date: Fri Oct 24, 2003 5:01:34 PM US/Pacific

Hello Everybody,
I am now modelling my skylight case, a 36' x30' room
with four 4' x 4' skylights distributed evenly.(well
depth 3'). In my Doe 2 model I am using a flat glass
which has properties similar to that of a
2 dome fiberglass(translucent) with Visible
transmittance = 0.5, SC = 0.45
I need to create a similar glass type in Radiance.
I am using the trans material type and based a on
previous discussion have created

void trans skylight
0
7 0.54 0.54 0.54 0 0 1 0

Is this the correct material definition.
What would be the definition for a similar white
translucent material.(Would the color effect the
illuminance values inside)

How did you come up with 0.54 for the diffuse? I would have expected this to be 0.50 if all you wanted was a 50% visible transmittance. However, there is no material that transmits 50% of the visible diffusely without also reflecting a fair amount. Given that you only care about the interior values, I suppose it doesn't matter in this case, but a more realistic model would be:

void trans skylight
0
7 1 1 1 0 0 0.5 0

This would be an ideal scattering surface, spreading the incident radiation equally in all directions, 50% transmitted and 50% reflected. There is no such material in the real world, but some materials come reasonably close. The diffuser is white because all of the components (red green and blue) are equal. A colored surface would affect the illuminances somewhat.

Also I know that I need to use mkillum for this.Do I
need to define both the window surface as well as a
polygon below the well as illums or simply the polygon
below the well so as to obtain accurate results.
Please Guide me with this.

In this special diffuse case, you can hand the skylight polygons to mkillum directly, setting

#@mkillum d=0 c=n l-

In the scene file to compute a total average diffuse light source for each surface using mkillum. There is no sense in creating illum's (as opposed to light sources) because there is nothing to see through such a diffuser, and no sunlight will penetrate it.

-Greg