Abstract : In order to measure the energy spread of electrons emitted from various negative electron affinity cathode structures, a simple apparatus using a uniform retarding field inside night vision tubes and customized tubes (all made by Intevac) was constructed and initial measurements performed. GaAs and GaAsP photocathodes with CsO activations were measured. Energy spreads as low as 100meV were observed from a low quantum efficiency GaAs cathode. An extremely sharp (30meV width) vacuum-level cutoff in the energy distribution from the GaAsP was observed. These two results show both the possible energy resolution of the technique and the energy spreads achievable from negative electron affinity photocathodes. Energy distribution variation indicated the importance of scattering in the band-bending region, and thus suggested the possibility of heterostructure and doping variation at the surface to minimize the energy spread. A design for an optimum cathode was developed.