Regarding the calculation of transmittance of objects, we need to tell that it is not possible to calculate such effects in DIALux as the calculation kernel is not able to calculate transparent surfaces yet. The only exceptions are windows, which can only be placed on room surfaces.
At the moment the only way to create a glass effect is to use the integrated Raytracer PovRay. To modify the settings for PovRay please follow this brief instruction:
Please select the object and choose in the inspector tab "surfaces". Subsequently mark all the surfaces you would like to modify and choose tab "Raytracer" on the right-hand side. On this tab you can make the necessary settings for the rendering (transparency, reflection, roughness). In this way you can simulate transparent or mirroring surfaces. Please keep in mind that you will get a realistic visualisation with PovRay but no calculation results in DIALux.