Integrated photometric properties of open clusters

Galactic open clusters provide an abundant sample of stellar aggregates of various sizes, ages and metal abundances, apt to constitute a template for comparison with star systems in other galaxies. In this paper we present and discuss a standard methodology to synthesize {\sl U,B,V} fluxes and colours, and apply it to a set of 138 open clusters. Results are compared with previous available ones in the literature. We were able to calibrate a mass--luminosity relation by which we evaluated the mass of $\simeq 400$ open clusters, leading to a well defined present--day mass function. The number--complete sample of galactic open clusters presented in Battinelli \& Capuzzo--Dolcetta (1991) is enlarged of a $15\%$.}