This work applies theoretical and computational methods to investigate the relationship between phosphorescence lifetime and the electronic character of the lowest triplet state of aromatic carbonyls. A formal analysis of the spin-perturbed wave functions shows that phosphorescence is due to a direct spin-orbit coupling mechanism modulated by permanent dipoles when the T1 minimum is 3 nπ*. If the minimum is a totally symmetric 3 ππ*, phosphorescence is due to an indirect spin-orbit coupling mechanism involving transition dipole moments with other excited states. The magnitude difference between permanent and transition dipoles leads to a much faster 3 nπ* phosphoresce than 3 ππ*. These predictions were verified with phosphorescence lifetime simulations of benzaldehyde and its three derivatives in the gas phase employing a vertical approximation and the nuclear ensemble approaches. Both predict 3 nπ* emission within a few tens of milliseconds. While the vertical approach indicates a 3 ππ* emission within a few seconds, vibronic corrections bring this value down to about 200 ms.