Use same LUN for all output spectra of each type (Radiance,
transmission, etc) by opening/closing files after writing data for each
Use individual LUNs for all output spectra, maintained 'open' throughout.
The purpose of this Flag is to allow large numbers of
output files to be written
where this exceeds the number of available
LUNs on certain machines (at the expense of slower run-time due to more