Spectroscopic effective temperatures of field objects (squares) and young objects (dots) compared to those derived from T_eff vs spectral type conversion scales valid for old field dwarfs (Stephens et al. 2009, black line) and young objects (dashed and/or dotted lines; Luhman et al. 2003b; Briceño et al. 2002; Luhman et al. 2004, 2008). The spectroscopic temperatures were found comparing the NIR spectra (IRTF, NIRSPEC, SINFONI) to synthetic spectra of the DRIFT-PHOENIX and BT-SETTL libraries (filled symbols), or fitting spectral energy distributions built from the typical colors of young objects (open circles; Luhman et al. 2010) or from the photometry of field dwarfs (open triangles; Patten et al. 2006).