 The mass-to-light ratios of galaxies and clusters are all much greater than due in part to the fact that most of the matter in these objects does not reside within stars and observations suggest that a large fraction is present in the form of dark matter.Luminosities are obtained from photometric observations, correcting the observed brightness of the object for the distance dimming and extinction effects.In general, unless a complete spectrum of the radiation emitted by the object is obtained, a model must be extrapolated through either power law or blackbody fits.