I've generated some 2nd order SH light-probes from cube-maps in my scene and I was surprised how strong artifacts are around the back of the dominant lights. I switched to a Lambert source plus ambient and got a result just like in the image below. Stupid SH Tricks seems to be suggesting a convolution filter of some kind to filter out the ringing, but I'm clueless on what a Han function is or how to apply it. Little help?
[attachment=19354:ringing.jpg]