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We examine the luminosity function of white dwarfs (WDs) in the local``complete'' WD sample ($d<20$ pc) of Holberg et. al. 2008. We find that thefraction of bright and young WDs is anomalously high among the WDs detected inmultiple systems with main sequence (MS) companions compared to that of thesingle WDs and theoretical expectations. This indicates a significantobservation bias against finding relatively faint WDs in multiple systems. Atthe bright end ($M_V<11.5$), the amount of WDs with MS companions isapproximately equal to that of single white dwarfs, indicating that $\gtrsim50\%$ of WDs have MS companions, consistent with the high multiplicity fractionof early-type MS stars. If true, a significant fraction of WDs in multiplesystems within 20 pc may have not been detected yet, and the number density ofWDs in the solar neighborhood and elsewhere may be up to twice as much aspresently believed.

Luminosity function suggests up to 100 white dwarfs within 20 pc may be hiding in multiple systems