How do I create a circle-pattern effect on window-glass?

Question

I'm currently working to re-create this little scene in my windowsill in Blender with Cycles.

My window-glass is covered with a thin sheet of plastic, which has a circle-pattern on it. This gives the following lighting-effect:

QUESTION: How do I create the circle-pattern effect on the window-glass?

• Do I need to model an extra glass layer on top of the existing glass-pane?

• Can this be done by adding a transparent texture to the window-glass-material ?

• Can this be done through adding a extra Cycles shader to the window-glass-material?

Answer 1

It can be done by applying a texture to the Displacement input of the glass material node. The glass must have some roughness to it.

You can use a texture like this one, made of two circles shifted by half their diameter and ridged in a concentric fashion (in your picture it looks more like an hexagonal packing, so if you're going for an exact copy you shouldn't use my mockup):

Then assign a material to the glass. I suggest using Principled BSDF with nearly 1.00 transmission; it must have some roughness in order to scatter light (the higher the roughness, the stronger the halo). Just plug the image texture into the Displacement socket of the Material output, but make sure to strongly decrease its effect by using a Math > Multiply node and setting the value to a very small number.

Finally, you should get something like this:

P.S. A realistic window wouldn't be just a plane, but rather a solid. Make sure that you don't apply the texture to the opposite face too.