  We model optical absorption of monolayer and bilayer graphene on hexagonal
boron nitride for the case of closely-aligned crystal lattices. We show that
perturbations with different spatial symmetry can lead to similar absorption
spectra. We suggest that a study of the absorption spectra as a function of the
doping for almost completely full first miniband is necessary to extract
meaningful information about the moire characteristics from optical absorption
measurements and to distinguish between various theoretical proposals for the
physically realistic interaction. Also, for bilayer graphene, the ability to
compare spectra for the opposite signs of electric-field-induced interlayer
asymmetry might provide additional information about the moire parameters.
