Declaration: TSpdc.SpectralRange (var RangeLow, RangeHigh: double): integer;
The function SpectralRange determines the wavelength range which the spectral descriptor requires for its correct application. The variable parameters RangeLow and RangeHigh return the lower and upper limits.

The function returns the following error codes:

 0 ... everything is OK
-1 ... invalid or unknown descriptor mode (should never occur)
-2 ... virtual descriptors cannot be evaluated here