  We present detections of methane in R of $\sim$1300, L band spectra of VHS
1256 b and PSO 318.5, two low gravity, red, late L dwarfs that share the same
colors as the HR 8799 planets. These spectra reveal shallow methane features,
which indicate VHS 1256 b and PSO 318.5 have photospheres that are out of
chemical equilibrium. Directly imaged exoplanets usually have redder near
infrared colors than the field-age population of brown dwarfs on a color
magnitude diagram. These objects along the L to T transition show reduced
methane absorption and evidence of photospheric clouds. Compared to the H and K
bands, L band (3 micron - 4 micron) spectroscopy provides stronger constraints
on the methane abundances of brown dwarfs and directly imaged exoplanets that
have similar effective temperatures as L to T transition objects. When combined
with near infrared spectra, the L band extends our conventional wavelength
coverage, increasing our understanding of atmospheric cloud structure. Our
model comparisons show relatively strong vertical mixing and photospheric
clouds can explain the molecular absorption features and continua of VHS 1256 b
and PSO 318.5. We also discuss the implications of this work for future
exoplanet focused instruments and observations with the James Webb Space
Telescope.
