Difference between 'Optical Spectral Type' and 'IR Spectral Type'?

[omoplata]

In the list of L and T dwarfs at 'dwarfarchives.org' (http://ldwarf.ipac.caltech.edu/archive/version5/viewlist.php?table=ltdwarf&format=html") there are two columns named 'spectral_type_opt' and 'spectral_type_ir'. I guess this comes from the type of instrument used in the measurements?

If I'm correct, the Spectral Type indicates the surface temperature of stars. If so why would the optical and infrared spectra give two different measurements? Which one is more accurate? Since the visual spectra of L and T dwarfs are very faint, would the 'infrared spectral type' be more accurate?

 

[Chronos]

The optical band, usually referred to as the V-band spectrum, is a small slice of the EM spectrum. The IR spectrum is much wider. Most objects in the universe are brighter in the IR spectrum - especially those with low V-band emissions.