Accurate Light Transmitting Fabric?

[Ibear888]

Hello,

Does anybody have a work flow to accurate light modeling and analysis of transparent mesh, shade or curtain fabrics?

In the attached, you can see that the light reflecting off the background is intense for an observer in the interior. It needs shades or curtains. How can I accurately model this?

Shade manufactures provide the light transmission value (Tv) of their fabrics, sometimes as a percent of transparency and sometimes as a percent of openness. However, setting a generic fabric to that transparency seemingly omits the reflectance, refraction, etc due to other factors such as the shape of the weave, reflectance, refraction, etc.. In the third attached image, I've modeled a 1 percent open shade fabric based on the waft and weft and yarn diameter of a particular fabric - 9608 extrusions for a single 13' x 6.6' roller shade. This does not seem like a practical solution.

I would love to hear from others who may have a work flow for accurate light analysis of shade fabric.

Thank you for considering my question!
Best, Jeff

[Peter.Chaushev]

Hello, Ibear888 ,
Apologies for leaving your question unanswered for so long!
Currently, there is no ideal solution for translucent surfaces although we have something in development.

When it comes to lighting analysis, a material's opacity value can linearly affect the amount of light passing through any objects that use it. (or alternatively refraction values with IOR=1).
This, however, is not something that would produce accurate visual results.

A new fog scattering model will be introduced with the next V-Ray 5 for Rhino update.
It is a sub-surface scattering model (SSS) that works well in combination with another upcoming option named 'Thin-Walled' refraction. They should help you with properly visualizing curtains while maintaining the functionality of the Lighting Analysis render element.

Kind regards,
Peter

[Ibear888]

You write, "When it comes to lighting analysis, a material's opacity value can linearly affect the amount of light passing through any objects that use it. (or alternatively refraction values with IOR=1)."

Although it would not produce accurate visual results (such as a fabric mesh shade), would it produce accurate luminance readings? For example, say I have a surface I assign gray plastic as a material and set its opacity to 10%. Testing shows that doing so will reduce luminance values for rays projecting through the material, but is it accurate? If a shade manufacturer says their product has a light transmission value of 10%, will the luminance readings through the 10% opacity material be accurate (knowing the visual rgb image will not be accurate)?

Thanks,
Jeff

[Peter.Chaushev]

Although it would not produce accurate visual results (such as a fabric mesh shade), would it produce accurate luminance readings?

Not entirely, as the opacity value will simply allow all rays to pass through at a certain percentage of their intensity. No light scattering will occur within the shade object.
The resulting analysis will be a rough approximation.

Regards,
Peter