To be fair, the photon self-interaction is usually negligible (barring the right medium and high energies), while for gluons it’s most of the story. Unless you’

To be fair, the photon self-interaction is usually negligible (barring the right medium and high energies), while for gluons it’s most of the story. Unless you’re looking at exotic situations, photons are well behaved, but gluons are many flavors of pain.