While tidying out my workshop I found those pieces of plexiglass tube with a translum coating. What a perfect diffusor!
I see a big lava lamp - 21st century edition - coming. 
Tell us more about this coating? That’s pretty sweet.
“Trans-Lum” or “tranlum” is the name of the material. Photographers use it. The tube you see is basically transparent and has 2 layers of it - one inside and one outside - that gives the diffusion more depth. But one layer does a great job , too.