  We present evidence which indicates the luminosity functions of star forming
regions, open star clusters and the field dips between spectral types M7-M8. We
attribute this to a sharp local drop in the luminosity-mass relation and
speculate that this is caused by the beginning of dust formation in the
atmospheres of objects in this effective temperature regime. This effect is not
predicted by the current generation of low mass stellar/substellar evolutionary
models. If our interpretation is correct then this result has important
implications for investigations concerned with the mass functions of star
forming regions and young open star clusters. For example, it suggests that
some brown dwarfs have higher masses than previously thought.
