Greetings!

I was wondering something about glass material.

Let’s say we have following glass material definded:

``````void glass transparent
Ø
Ø
3
1 1 1
``````

This kind of material should pass all the light through, right? That being said, transmittance of this material would be 100%.
Note: I’m aware that this kind of glass doesn’t exist, but let put physics aside, i’m thinking just about how radiance treat those parameters.

Now, how radiance will treat this kind of material:

``````void glass red
Ø
Ø
3
1 0 0
``````

Does this mean that only 1/3 of light will pass this glass? Of course this material will be reddish, and it will affect the calculation in some way.

I would be grateful to hear your thoughts upon this.

Regards,
Pavle

The glass with transmission values of 1 1 1 will not have 100% transmittance unless the index of refraction is also 1.0. This is due to physics and the fact that the front and back surfaces of a glass pane will reflect some small percentage of light, so about 8% of light is reflected and only 92% transmitted at normal incidence. The fraction of reflected light also increases with the angle of incidence, becoming nearly 100% close to grazing.

For your second question, the amount of light in each of the RGB channels is treated separately, but R, G, and B do not necessarily contain 1/3 of the energy. If you really want 1/3 of the energy to be absorbed, then set all three channels to 0.3333. All you can really say about glass with transmission factors of 1 0 0 is that no red light is absorbed, but all green and blue light will be. (Note that there will still be about 8% reflection in red, and 4% reflection in green and blue.)

I hope this is useful. Your questions are lacking context.

-Greg

Dear Greg,

First of all, thanks for the fast reply.

Yes, I’m aware of those losses, I was talking from the radiance aspect regarding the glass primitive.

What I’m trying to achieve here is to export some Revit windows as radiance primitive. In Revit you are able to set the tint of the window in RGB format and reflection of it also.

Now, with that being said, I hope it’s clear now.

Also, any further help or guidance is appreciated.

Regards,
Pavle

Hi Pavle,

One thing to note here is that the glass material in Radiance is designed for use with surfaces not solids or geometry with “thickness.” So you may need to account for what kind of geometry is being used to represent glazing systems in Revit in order to get the kind of geometry that would be appropriate for use in Radiance.

-Jack de Valpine

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