This work is based on the study of the evolutive variation of the luminosity function in open clusters, Ψ_a (M_v ; t), and consists in a critical survey of such a function's initial appearance. In chapter I, we indicate some of the main results about the rate of stellar evaporation in clusters and we extend Spitzer and Härm's computation to the case of nonisolated clusters. In chapter II, we show how to compute the evolution of the luminosity function caused by evaporation. In chapter IV, we take into account the influence of stellar internal evolution during the cluster's life. Then we compute the evolution of according to various choices (chap. III) of the initial luminosity function and we apply the results to a cluster of intermediate age (chap. V). In chapter VI we consider the case of old clusters. Finally the results obtained in some peculiar cases of well known clusters of various ages in the neighborhood of the sun lead us to deny the universal character during time of the faint part of the initial luminosity function.