Glazing Material (for glare)

radiance-general
1

Hi all,

I am trying to assess glare from a neighbouring building’s glazing. What would be an appropriate material to be used for the glazing? I have read that dielectric or trans may be applicable (with trans being hard to use) because both of them can consider transmissivity, diffuse reflectance, and specular reflectance. Would appreciate it if someone could provide some pointers! I have done some searching around in this forum and I can’t seem to come to a conclusion.

Thank you!

Kenneth

2

Hi Kenneth, welcome to the Radiance discourse forum.

The solutions you mentioned sound more complicated than necessary. Do you know the specular reflectance of the neighboring building’s glazing? That will be the dominant contributor the glare when the sun reflects off of the neighboring building. You could model the glazing as a mirror with that reflectance for a simple calculation.

For more complexity (including Snell’s law to incorporate the the angular dependence of reflection), you could use a glass material. Dialectrics would help you consider details of refraction, which you don’t care about in this case, and trans would allow you to simulate a diffuse reflection, which also doesn’t seem relevant to the case you’re investigating.

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3

HI Nathaniel,

Thanks for the quick response. The neighbouring buiding’s glazing is unfortunately not known. We however do know a local guideline limiting the total reflectance of glazing to 20% which we might use as the assumption, but I am unsure how this can be translated to specular reflectance; is it reasonable to assume negligible diffuse reflectance i.e. all 20% is specular reflectance? On the other hand, do you know if there is a database of some sort where I could get typical reflectance values (including specular reflectance) of different types of glass?

Thanks!
Kenneth

4

Hi Kenneth,

When you stand in front of the facade on a bright day, do you see a mirror image of yourself in the windows? If so, you may assume that all 20% of the reflectance is specular. Diffuse reflection from glass is unusual and would indicate that the glass is frosted, sand blasted, textured, or very dirty.

For data on typical glazing materials, you can check the International Glazing Database for typical glass materials or the Complex Glazing Database for frosted and non-glass materials.

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5

Hi Nathaniel,

Thanks, that’s very helpful, let me try to work with that!

Kenneth

6

If you don’t see yourself in a mirror, I think you may have bigger problems.

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