  We report on electron cooling power measurements in few-layer graphene
excited by Joule heating by means of a new setup combining electrical and
optical probes of the electron and phonon baths temperatures. At low bias,
noise thermometry allows us to retrieve the well known acoustic phonon cooling
regimes below and above the Bloch Gr\"uneisen temperature, with additional
control over the phonon bath temperature. At high electrical bias, we show the
relevance of direct optical investigation of the electronic temperature by
means of black-body radiation measurements that provide higher accuracy than
noise thermometry. In this regime, the onset of new efficient relaxation
pathways involving optical modes is observed
