I made a few tests.
1 - I went to this website that has loads of transparent textures.
2 - In the Sketchup Warehouse I found a nice set of modular vertical blinds .
3 - I then made a few renders, applying a transparent texture to the blinds.
right image - Q4 using PVR with default settings, in the renderer I checked Enhance External Brightness, unchecked Add Ceiling Lights, 800x690 pix, rendering time 6-7 minutes
left image - (probably?) same settings, but I added a halogen light in the exact middle of the room (strength 50%, 100x100 cms), 800x690 pix, rendering time 49 minutes
original image
