  Velocity bias offers a single parameter ($b_v$) description of the likely
segregation of mass and light in a galaxy cluster. The relation between the
projected mass profile and the light profile, normalized by the virial $M/L$,
is presented as a function of $b_v\equiv\sigma_\ell/\sigma_\rho$, the ratio of
the RMS velocity dispersions of the galaxies and the underlying dark matter.
The light distribution does not trace the mass at any radius within the
cluster. At the apparent harmonic radius the gravitational mass can exceed the
virial mass calculated from the light by about a factor of 2 (or more). The
data for the MS1224+20 cluster, covering nearly a decade in radius, are well
described by a velocity bias value of $b_v=0.85\pm0.05$, comparable to the
n-body estimate of $b_v=0.8\pm0.1$. This particular value will remain tentative
until more data are available.
