> It works because surface properties is used even if there's no lights in
the scene; surface
> illumination is used once per every light. This is why the HDR suddenly
worked when you added a > weak light to the scene.
OK, that explains it. I had assumed that a Surface Illumination shader would
define illumination, say light. Now, with your explanation in mind I've
re-read the manual about it and understand that, simply put, a Surface
Illuminations shader defines how the surface will react to light. Thank you
for that.
Frank
