In this paper we partly revise our previous model (Appl Phys Lett 1998;73:1874) of field emission from amorphous carbon nitride films a-C:H:N based on more detailed electronic structure calculations. Our revision does not change the basic mechanism for electron emission but concerns the values of the band gap and electron affinity used in the model. Calculations of the density of states and optical functions (Tauc plots) are given, which support these values and which, furthermore, support the nature of the emitting states. Also an alternative mechanism of field enhancement is adopted. A better overall agreement with experiment is obtained. The relevance of this work to emission from carbon nanotubes is also discussed.