yes, that's the point.  if all directional lites are zero (dark scene), then a surface with alt_diff=0
would not glow in the dark.  otherwise, that and sevl. other channels will emit lite
with IDL/GI activated.

p.s. I was hoping some of them would try exposure control, but apparently they won't.
in re: poser, GC is the thing with much more extensive explanations.