For the realization of low-voltage full-color FEDs, requirements for phosphor for the FED are proposed. Especially, the influence of released gases or substances from phosphors on the field emission within the FED was made clear. It was clarified that the analysis of F-N plots of the V-I curve of field emission characteristics was helpful to know the interaction of field emission and phosphors. In the experiment, we first obtained the depth from the phosphor surface of the low voltage electron excitation in case of ZnGa2O4, where the region available for cathodoluminescence at the anode voltage of 400 V is about 63 nm deep from the surface. The characteristic of the 12.4 cm-320(trio)240 pixels low-voltage full-color FED is reported. The luminance of 154 cd/m2 was attained at the anode voltage of 400 V and the duty factor of 1/241. Supported by the high potential of the FED as a flat panel, each problem shall be steadily solved to secure the firm stand as a new full color flat display in new applications.