We combine cryogenic storage of fullerene anions up to minutes with laser photo-detachment spectroscopy and measure the electron affinities to be 2.684(3) eV for C60 and 2.7665(3) eV for C70, which settle long-standing issues concerning these values. We find that C−70 cools more efficiently than C−60 and that this is due to differences in photon emission from electronically excited states populated by inverse internal conversion (recurrent fluorescence). We also find that intramolecular vibrational redistribution is no longer effective at low internal energies of C−60 or C−70. Radiative cooling becomes extremely slow below intramolecular vibrational redistribution decoupling energies of 0.32(2) and 0.13(3) eV for C−60 and C−70, respectively.