SKyScraper Lighting by InTheCity
I also have a separate glass layer that will be utilizied later on.
I begin with a base material, that will serve as a general feel for the illuminated rooms
After adding a few layers of Cel Noise with different blend modes. This will create enough of a random feel for work with.
You may want to spend the time making sure your cel noise is evenly distributed between floors. But it`s necessary for the effect to work.
Now i duplicate the original diffuse layer and copy it to Luminosity channel (Disable/Uncheck the Diffuse channel). I also then change parameters and scaling of the original Cel noise functions, as you don`t want the random noise to match the original material.
Experiment here with your layering and render some tests until you`re happy with your material. I`ve added a few layers of color to break up the intensity.
To test on a building, create a VrayBlendMaterial, add the lighting coat as a top layer and the base diffuse layer underneath.
I`m happy enough with initial test, i may multiply the light intensity from 1 to 4.
I now switch my focus over there glass material which will break up the intensity of illumination.
I created a glass material, with some diffuse from original cel noise function. The refraction layer has no special consideration, besides the IOR being 1.06
Before adding the glass to the building, my preferred method is to create a 2side Material using an image of your choosing for the translucency texture. Apply this to your glass using cubic mapping, Increase the scale for effect.
You can also experiment with a random "closed blinds" look, by adding one of your cel layers to the Glossy channel in the glass material.
I would suggest if you do this, to keep the mix strength low, to avoid lengthy render times.
The final result is ok, having started from scratch again. There is many ways in which this can go.
From drastically wrong, to pretty realistic, Judge for yourself.