  New theoretical evaluations of the RGB luminosity function 'bump' and the
ZAHB luminosity covering the range of metallicities typical of galactic
globular cluster are presented. The variation of the theoretical RGB bump and
ZAHB levels due to the metallicity, original helium content, mixing length
value, age, mass loss, bolometric corrections, opacities and equation of state
adopted in the evolutionary models is also discussed. These new prescriptions
have been taken into account for casting light on a longstanding astrophysical
problem connected with the Red Giant Branch evolutionary phase, namely the
discrepancy between the observational and the theoretical luminosity of RGB
bump. A sample of globular clusters with accurate evaluations of the bump
luminosity and spectroscopical metallicity determinations has been selected.
The Zero Age Horizontal Branch luminosity at the RR-Lyrae instability strip has
been evaluated as accurately as possible, and the observational luminosity
difference between the RGB bump and the ZAHB has been compared with the
theoretical values. It is shown that there is no significant disagreement
between observations and canonical stellar models. The possible applications of
this result are also briefly discussed.
