K_s-band luminosity functions for the entire W3 Main region and the different subregions constructed from only the K_s-detected sources. The dotted histograms are the observed sources binned with a bin size of 1 mag. The dashed histograms represent the histogram of the stars in the control field, scaled to the area of the corresponding subregion. The field-corrected histogram is plotted with a solid line. The vertical dotted lines represent the magnitude above which we are photometrically complete with a completeness of at least 50%. A linear fit yields the slopes indicated in the figures.