X-ray luminosity distribution as a function of the bolometric luminosity. The three pairs of lines refer to the (25%, 50%, 75%) quartiles of the L_X distributions calculated in running intervals of bolometric luminosity constituted by 80 contiguous points and smoothed in intervals of bolometric luminosity of 0.1 erg s^-1. The continuous line refer to the NGC 1893 stars, and the dashed one to the ONC stars.