Electroluminescence from single layer devices comprised of a solid state solution of an electron transport small molecule and an emitter molecule dispersed in poly(N-vinylcarbazole) is described. The use of molecularly doped polymers as the materials package and the single layer nature of these devices simplifies their fabrication by enabling spin coating techniques to be used. The color of the electroluminescence from these devices can be tuned across the visible spectrum by appropriate selection of the emitter molecule. In addition the use of molecularly doped polymers allows one to tailor the transport properties of the device. Incorporation of a hole transport small molecule in the polymer based film enables one to tune the mobility of the carriers injected into the device from the indium tin oxide anode. Evidence will be presented showing that whereas the luminance from any given device increase linearly with the injected current density, the luminance observed from different devices is independent of the hole mobility. The critical determinant for the level of light output is the number of carriers injected into the device; how fast they move is unimportant.