Upper panel: Two 12 Gyr WD isochrones for the progeny of He-normal cluster sub-populations with [Fe/H] = −1.9 and −0.9 (solid blue and dotted orange lines, respectively), and a 12 Gyr WD isochrone for the progeny of the Y = 0.4 cluster sub-population (dashed green line). See text for details. Lower panel: LFs calculated from the three isochrones in the upper panel (same line styles and colours). The number of stars in each LF is the same, approximately equal to the total number of objects in the cluster LF.