Using a simulated disk brown dwarf ( BD ) population , we find that new large area infrared surveys are expected to identify enough BDs covering wide enough mass–age ranges to potentially measure the present day mass function down to \sim 0.03M _ { \odot } , and the BD formation history out to 10 Gyr , at a level that will be capable of establishing if BD formation follows star formation .
We suggest these capabilities are best realised by spectroscopic calibration of BD properties ( T _ { eff } , g and [ M/H ] ) which , when combined with a measured luminosity and an evolutionary model can give BD mass and age relatively independent of BD atmosphere models .
Such calibration requires an empirical understanding of how BD spectra are affected by variations in these properties , and thus the identification and study of “ benchmark BDs ” whose age and composition can be established independently .

We identify the best sources of benchmark BDs as young open cluster members , moving group members , and wide ( > 1000AU ) BD companions to both subgiant stars and high mass white dwarfs ( WDs ) .
To accurately asses the likely number of wide companion BDs available we have constrained the wide L dwarf companion fraction using the 2MASS All Sky Survey , and find a companion fraction of 2.7 ^ { +0.7 } _ { -0.5 } % for separations of \sim 1000–5000AU .
This equates to a BD companion fraction of 34 ^ { +9 } _ { -6 } % if one assumes an \alpha \sim 1 companion mass function .
Using this BD companion fraction we simulate populations of wide BD binaries , and estimate that 80 ^ { +21 } _ { -14 } subgiant–BD binaries , and 50 ^ { +13 } _ { -10 } benchmark WD–BD binaries could be identified using current and new facilities .
The WD–BD binaries should all be identifiable using the Large Area Survey component of the UKIRT Infrared Deep Sky Survey , combined with the Sloan Digital Sky Survey .
Discovery of the subgiant–BD binaries will require a NIR imaging campaign around a large ( \sim 900 ) sample of Hipparcos subgiants .
If identified , spectral studies of these benchmark brown dwarf populations could reveal the spectral sensitivities across the T _ { eff } , g and [ M/H ] space probed by new surveys .