We present detailed evolutionary calculations for carbon
- oxygen - and helium - core white dwarf (WD) models with masses ranging from
M= 0.1 to M= 1.2 solar masses and for metallicities Z= 0.001 and Z= 0. The
sequences cover a wide range of hydrogen envelopes as well. We employed a
detailed WD evolutionary code. In particular, the energy transport by
convectcion is treated within the formalism of the full spectrum turbulence
theory. The set of models presented here is very detailed and should be
valuable for the interpretation of the observational data on low - mass WDs
recently discovered in numerous binary configurations and also for the general
problem of determining the theoretical luminosity function for WDs. In this
context, we compare our cooling sequences with the observed WD luminosity
function recently improved by Leggett, Ruiz and Bergeron (1998) and we obtain
an age for the Galactic disc of approximately 8 Gyr. Finally, we applied the
results of this paper to derive stellar masses of a sample of low - mass white
dwarfs.