Judy,
Sorry about the spelling (or lack thereof). Collimated light is light
which is parralell or as if emitted from a point source at a distance.
And please note that a single lamp is not a point source. The sun can
be considered one because of its great distance. Optical systems may
achieve fairly parrallel light. However, these systems are not as good
as the sun for approximating a point source.
> ... Your observations make me wonder what the difference is
> > -- wavelengths ...
Yes, I believe that various wavelengths will render difering results,
although I have not had the opportunity to test this. The collimated
light also makes a difference. A simple comparison is to expose the
same negative in direct sun and in the shade of a tree. (different
exposure times of course.)
> Have you ever considered foregoing test exposures?...
No way. When I am about to expose a 10" by 45" print on fabric (which
uses three times the chemistry as that for paper)(and I am doing Pt/Pd)
I always make a smaller test print, even if I know the printing time.
Risk management.
Jeff