[Radiance-general] Spots when recreating Turrell installation

[Mark Stock]

Folks,

If you have the chance to go to the Guggenheim in NYC, go and see the
James Turrell exhibit. You've never seen the Guggenheim quite like
this before, and as appreciators of light and its behavior, you will
find yourself both satisfied and intrigued by his installations.

I've been working to recreate a few of them in Radiance, and am
running into some difficulties. One piece, "Afrum I (White)", should
look like this:
http://nyogalleristny.files.wordpress.com/2013/08/afrum1.jpg

It's a point light in a small box above the entryway to the room, a
special 6-sided hole cut in the wall, and the light beams this
cube-like shape onto the corner. The light patch illuminates the room.

Instead, what I get looks like this:
http://markjstock.org/transfer/img06.png

Here are the relevant rendering parameters:
-ds 0.02 -lw 1e-5 -ab 5 -aa 0.03 -ar 256 -ad 1024 -as 512

I suspect that I simply need more ambient subsamples, as a few ambient
points are catching the patch and some are not. But increasing -ad and
-as do nothing to improve quality.

Or, WAIT, are those bright spots seeing the little hole (it's 6" wide)
through which the light is originally emerging? How can I prevent
that?

Mark