  White dwarf cooling sequences provides a useful indicator of the evolutionary
time scales involved in the chronometry and star formation history of the
galactic disk and, for this reason, the luminosity function of white dwarfs has
become a powerful tool for studies of the evolution and formation of the Milky
Way.
  We examine the faint-end ($M_V > +14$) behavior of the disk white dwarf
luminosity function using the $1/V_{\rm max}$ method, but, for the first time,
fully including the effects of realistic observational errors in the derived
luminosity function.
  We find that observational errors, mostly in the bolometric corrections and
trigonometric parallaxes, play a major role in obliterating (real or
artificial) small scale fluctuations in the luminosity function. A better
estimator of the true luminosity function seems to be the median over
simulations, rather than the mean. When using the latter, an age of 10 Gyr or
older can not be ruled out from the sample of Leggett, Ruiz, and Bergeron
(1998).
