Top panel: total luminosity and luminosity density of field galaxies ploted against the effective radii of the voids to which they belong. Larger voids are less luminous in the observation than in the simulation. This disagreement becomes more significant when faint objects are also taken into account, as shown in the two plots of the lower panel. Observed voids are clearly less luminous than simulated voids. Note that the luminosity cutoffs are the same for the observation and the simulation when faint galaxies are taken into account. We expect this discrepancy to be even more significant than shown here because our Millennium I simulation uses a higher value of σ₈ than given by WMAP7.