Thanks for the comments, it’s always interesting to hear what people think.
I experimented with different ground planes, a uniform colour was good for showing off the shadows but looked flat and was oddly more distracting than one with a bit of texture. If I used anything with with stripes, checkers or grids of any kind I found I was being forced to line all the objects up exactly with the ground pattern So the random circles it was.
An animation is an interesting idea; any rotation other than perpendicular to the camera would break the illusion although it may be possible to have the triangles slide through each other in an impossible way I will need to think about that. No promises.
Feel free to use it as a background, desktop or what ever. The .blend file is on Blend Swap and is CC0 there’s a link in my previous post.