Why no BLF Lumen Sphere?

Doing a thread bump here because I’m helping with this: BLF Sphere Please read the thread to understand the goal with it- we’re not looking for perfect, but rather consistency with common calibration so folks can compare with each other equally. I have done a search here for “IS” and”Sphere” and went back to read all the numerous posts, and it seems this thread is the best for my questions.

At present I’m looking at styrofoam sphere sources but a few thoughts have crossed my mind. First is that Hannes started on an ABS sphere- do you think it would be a viable alternative to styro if the inside was coated with flat white paint? Any ideas on alternative cheap store-bought sphere materials? Would not want to do more than sand or paint these since there’s going to be dozens of these made.

Also what do you think of painting the inside instead of sanding? I have the proper spray equipment and paint which would make it easy and a lot faster than sanding. Remember dozens are being made and time matters!

Any other relevant thoughts on sourcing the sphere portion cheaply are appreciated.

Phil