Or, I Could Do Something Like This:

In this concept, there would be a helical-spiral perf metal screen which would act as a diffuser.  The source would be an MR-16 or similar mounted in the base, pointing up.  The perf screen is generated as a parametric surface governed by the following equations:

X(u,v) = cos(u)+1.5*u*sin(u)

Y(u,v) = sin(u)+1.5*u*cos(u)

Z(u,v) = .5*u*v

u ∈ [4, 15], v ∈ [1.5, 27]

Looks complicated, but the shape is just a trapezoid rolled up into a cylinder.  I like the moire-interference pattern cast by the overlapping layers of perf metal, but in order to get a nice clean finish on the edges I’d have to wrap them in some kind of metal beading, as well as support the whole thing with vertical rods, and I’m not sure I can do that without welding.  So the screen might end up being handmade paper or something like that.