A typical continuum detector (e.g. a CCD) collects photons over a finite wavelength range e.g. 0.1 to 0.2 nm. Its response is not usually linear as a function of wavelength. Moreover, although there are standard definitions for different wavelength bands (U B V R I in the optical, see http://ads.harvard.edu/books/hsaa/idx.html etc.), different instruments have slightly different cut-offs. Hence for very accurate work you need to know the filter (Cousins, Johnson etc.) as well as the band. Ideally the VO would have a look-up table of the band-pass shape for each filter.

But for ResourceMetadata the broad definitions are fine..

-- AnitaRichards - 24 Apr 2003