Hi

I want to use a translucent material that I have  some of it'sparameters (solar transmittance,solar absorption,solar reflectance,visible light transmittance) ,  revealed in it's catalog.

as you see they are not the same, defined by radiance:

modifier trans ID

0

0


7 redTransmission greenTransmission blueTransmission specularity roughness transmissivity transmittedSpecular



do you have any recommendation?what should I do?

one of my friends recommended me  use below method:

 to define available parameters in Ecotect and then export  them in radiance in order to get  the desired parameters but  when  I give visible solar transmittance more than 25 it gives me a material that is named glass with 3 parameters.in case of less than 25 it is ok; it  gives a material named translucent.. with7 parameters.

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Hi Mona,

The trans material type is one of the trickiest to get right, but there is some official word on it,

Trans is a translucent material, similar to plastic. The transmissivity is the fraction of penetrating light that travels all the way through the material. The transmitted specular component is the fraction of transmitted light that is not diffusely scattered. Transmitted and diffusely reflected light is modified by the material color. Translucent objects are infinitely thin.


mod trans id
0
0
7 red green blue spec rough trans tspec

So, if you want to calibrate it yourself, red green and blue are just colors. Specularity and roughness are the visual characteristics of reflected light, just like when you define a plastic material. Transmissivity is the amount of all light (scattered and not scattered) that makes it through the material. Tspec is the percentage of the transmissivity that is specular. 

Best,

Alstan

Hi,

1. I have a similar problem to solve. In my case however shall be the standard solution. I want to add two types of solar glasses.  SunCool 66/33 and 70/40. How can I transform my data into  RGB colors?

2. How we could add this also to thermal material?

I read how to define glass but have no idea how to apply that in my products?

glass

modifier glass id

0
0
3 redTransmission greenTransmission blueTransmission

# A transmission value of 0.96 is typical, for standard 88% transmissivity glass.

# Single Pane
# visual transmittance: 88.4%
# visual transmissivity: 96.2%
void glass SinglePane
0
0
3 0.962 0.962 0.962

SunCool Glass

Hi Michal,

Since you have T_vis (but no spectrum-specific data), it is probably best to just translate it into transmissivity and assume a neutral color, but the proper quantity, of light passing through the window. To translate between transmittance to transmissivity, there is a useful formula: 

tn = (sqrt(.8402528435+.0072522239*Tn*Tn)-.9166530661)/.0036261119/Tn

tn = transmissivity (used by the glass material)

Tn = Transmittance

It can then be plugged into your material definition above.

Best,

Alstan

Hi Alstan and thread-

I have a similar question regarding how to apply the VLT (visible light transmission) given by a manufacturer into a radiance material. We are using glazing with a 42% VLT rating. My understanding was that the RGB values were transmittance, not transmissivity. Is this correct? If not, do I need to set a thickness for my geometry in Rhino? Right now my glazing panels are planes without thickness. Below is what I have set for the glass right now but maybe I need to use your formula above to translate my VLT into transmissivity? Any help would be much appreciated!

# solarban R100
# visual transmittance: 42%
# visual transmissivity: ???
void glass solarban R100
0
0
3 0.42 0.42 0.42

Hi Ben,

Radiance uses transmissivity in its material definitions. You should be able to use the equation above to transmit VLT into transmissivity and use it in your material definition.

A little aside, you will note that the default glass materials in DIVA all work like this too,

# Single Pane
# visual transmittance: 88.4%
# visual transmissivity: 96.2%
void glass SinglePane
0
0
3 0.962 0.962 0.962

Best,

Alstan

Thank you! That makes sense about the default- I should have looked at that more carefully. Thanks for the equation.

Now I can translate transmittance into transmissivity but I would like to be able to explain it as well. The dictionary definitions aren't very helpful except to say that transmissivity is "equal to the internal transmittance of the material under conditions in which the path of the radiation has unit length." What exactly is the difference between transmittance and transmissivity?

I believe the difference is that transmittance accounts for internal reflections in a material with volume, while transmissivity is needed for the "glass" material type that has no real thickness. see here: http://www.radiance-online.org/pipermail/radiance-general/2010-Nove...

If it is on the Radiance list, it is Gospel, no? :D

Max

Hi Ben and Max,

For completion, there is a very good discussion of the two terms on Schorsch's website.

Regards,

Alstan

Hi, Alstan.

I was reading this discussion and have one doubt.

The definition of trans materials is:

3 RED Transmission GREEN Transmission BLUE Transmission specularity roughness transmissivity transmittedSpecular

The RGB value is not transmissivity in given colour wave length?


 
J. Alstan Jakubiec said:

Hi Mona,

The trans material type is one of the trickiest to get right, but there is some official word on it,

Trans is a translucent material, similar to plastic. The transmissivity is the fraction of penetrating light that travels all the way through the material. The transmitted specular component is the fraction of transmitted light that is not diffusely scattered. Transmitted and diffusely reflected light is modified by the material color. Translucent objects are infinitely thin.


mod trans id
0
0
7 red green blue spec rough trans tspec

So, if you want to calibrate it yourself, red green and blue are just colors. Specularity and roughness are the visual characteristics of reflected light, just like when you define a plastic material. Transmissivity is the amount of all light (scattered and not scattered) that makes it through the material. Tspec is the percentage of the transmissivity that is specular. 

Best,

Alstan

Hi Alstan,

I have a clarification on this. Does the total transmissivity of the glass equal the RGB values multiplied by the trans value?

For example, if I have a definition of

void trans test_01

0

0

7 0.5 0.5 0.5 0.1 0.1 0.6 0.4

Does this mean that the total amount of light that gets through is represented by 0.5 (RGB number), 0.6 (Trans number) or 0.3 (0.5x0.6)? Also - doe the 0.4 tspec number mean that 40% of light that gets through is cattered, or does it mean that 40% of the light that gets through is not scattered. 

As always - thanks for your help!

Vikram

J. Alstan Jakubiec said:

Hi Mona,

The trans material type is one of the trickiest to get right, but there is some official word on it,

Trans is a translucent material, similar to plastic. The transmissivity is the fraction of penetrating light that travels all the way through the material. The transmitted specular component is the fraction of transmitted light that is not diffusely scattered. Transmitted and diffusely reflected light is modified by the material color. Translucent objects are infinitely thin.


mod trans id
0
0
7 red green blue spec rough trans tspec

So, if you want to calibrate it yourself, red green and blue are just colors. Specularity and roughness are the visual characteristics of reflected light, just like when you define a plastic material. Transmissivity is the amount of all light (scattered and not scattered) that makes it through the material. Tspec is the percentage of the transmissivity that is specular. 

Best,

Alstan

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