  We have developed a relativistic, radiation-hydrodynamics Lagrangian code,
specifically tailored to simulate the evolution of the main observables (light
curve, evolution of photospheric velocity and temperature) in core-collapse
supernova (CC-SN) events. The distinctive features of the code are an accurate
treatment of radiative transfer coupled to relativistic hydrodynamics, a
self-consistent treatment of the evolution of the innermost ejecta taking into
account the gravitational effects of the central compact remnant, and a fully
implicit Lagrangian approach to the solution of the coupled non-linear finite
difference system of equations. Our aim is to use it as numerical tool to
perform calculations of grid of models to be compared with observation of
CC-SNe. In this paper we present some testcase simulations and a comparison
with observations of SN 1987A, as well as with the results obtained with other
numerical codes. We also briefly discuss the influence of the main physical
parameters (ejected mass, progenitor radius, explosion energy, amount of
\chem{56}{Ni}) on the evolution of the ejecta, and the implications of our
results in connection with the possibility to "standardize" hydrogen-rich
CC-SNe for using them as candles to measure cosmological distances.
