Quintuplet luminosity functions of all filters (left: JHK_s, right: L′). All JHK_s luminosity functions are shown for the combined sample used for the main-sequence source counts. These luminosity functions therefore indicate the limitations of the source counts in the final JHK_s and JHK_sL′ catalogues relevant for the main-sequence and excess samples here, and not the true detection limits in each filter. The K_s luminosity functions are shown for both proper motion epochs used for membership derivation. Likewise, the L′ luminosity functions are derived from the matched JHK_sL′ source lists used for further analysis. The dashed line in the L′ luminosity function in Field 1 indicates the truncation imposed when combining F1 with the outer fields. The dashed lines in the L′ luminosity functions in Fields 2 and 5 indicate the faintest L-excess source in each field. Except for Field 4, all L′ data sets extend towards or beyond a sensitivity of L′ = 15.0 mag.