Image intensifier tubes and other electro-optical devices use phosphors as a part of their output structure, and the temporal behavior seems to be a source of confusion among those who specify the requirements for these devices. Some of these phosphors...in particular the common P-20...exhibit a "non-linear" charactristic, in that the decay behavior is strongly dependent on the duration of exitation, and less so on current density. This paper will attempt to clarify some of these issues for the spec writer, without any treatment of the physics or chemistry of the phosphor materials.