bands of the Johnson photometric system in the framework of a simple model with simultaneous star formation
and a Salpeter initial mass function. The presence of stars in the stage of gravitational compression in these clus-
ters leads to the appearance of two maxima and a valley in this luminosity function. Published observations of
luminosity functions for stars in young (
< 8) clusters show that most of them have statistically significant fine structure (maxima or valleys), similar to that predicted by the theory. The most reliable data (15 clusters),
satisfying requirements for completeness and freedom from field stars, were selected for comparison with the
theoretical luminosity functions. This comparison shows good agreement in the positions of theoretical and
observed features and in the general behavior of the luminosity function. The discovery that the “brightness”
of the maxima in the luminosity function
depend on time suggests a new method to determine the cluster ages. The observations reproduce the
–
relation well, but clusters with ages determined from the upper half of the main sequence are significantly shifted (
0.3 in 
) relative to the theoretical curve. Possible rea-sons for this disagreement are discussed.