  Brown dwarfs, stars with insufficient mass to burn hydrogen, could contribute
to the dark matter in the Galactic disk, galactic halos or even a background
critical density. We consider the detectability of such brown dwarfs in various
scenarios, extending previous work by allowing for the possibility that they
may have an extended mass spectrum or be clumped into dark clusters. We
investigate the constraints placed on such scenarios by the \iras survey.
Whilst an extrapolation of the mass function of visible disk stars makes it
unlikely that brown dwarfs comprise all of the proposed disk dark matter, \iras
does not exclude brown dwarfs providing the dark matter in our own halo or a
cosmological background. Neither does it improve on existing dynamical
constraints on the mass and radius of brown dwarf clusters in our halo. Future
satellites such as \iso and \sirtf will either detect brown dwarfs or brown
dwarf clusters or else severely constrain their contribution to the dark
matter.
