  We have measured the optical reflectivity $R(\omega)$ of the quasi
one-dimensional conductor $NbSe_{3}$ from the far infrared up to the
ultraviolet between 10 and 300 $K$ using light polarized along and normal to
the chain axis. We find a depletion of the optical conductivity with decreasing
temperature for both polarizations in the mid to far-infrared region. This
leads to a redistribution of spectral weight from low to high energies due to
partial gapping of the Fermi surface below the charge-density-wave transitions
at 145 K and 59 K. We deduce the bulk magnitudes of the CDW gaps and discuss
the scattering of ungapped free charge carriers and the role of fluctuations
effects.
