  We study light scattering from a periodically modulated two dimensional
electron gas in a perpendicular magnetic field. If a subband is partially
filled, the imaginary part of the dielectric function as a function of
frequency contains additional discontinuities to the case of completely filled
subbands. The positions of the discontinuities may be determined from the
partial filling factor and the height of the discontinuity can be directly
related to the modulation potential. The light scattering cross section
contains a new peak which is absent for integer filling.
