In an earlier post I was wondering whether the image projected on the floor was a bug. I got a dielectric sphere from Amazon and just set up a ugly ducking Cornell Box made out of foam-core. Apparently, spheres are more effective lenses than I realized and it is probably not a bug.
The projected image of the ipad is more visible on the floor than I expected.
I'll be doing a more full spectral validation of my renderer this week. It's fun in an artsy crafty first grade maker movement kind of way!