  We present a spectral analysis of a sample of late L dwarfs. We use our
latest model atmospheres and synthetic spectra and optical and K band spectra
to determine effective temperatures. We derive effective temperatures of 1400 K
to 1700 K for L8 to L6 dwarfs. The analysis demonstrates that our recent models
that rain out the formed dust completely are applicable to optical spectra of
late L dwarfs and that more consistent models are needed for intermediate L
dwarfs and for infrared spectra. We compare the results for the effective
temperatures with the temperatures of the onset of Methane formation. Our
models predict Methane absorption at 3.3micron to occur at about 400 K higher
temperatures than Methane absorption at 2.2micron. This is consistent with our
data and previous observations which show Methane absorption at 3.3micron but
not at 2.2micron in late L dwarfs.
