In electroluminescent devices electrons move every half period from the cathodic to the anodic interface of the phosphor layer and excite atoms which can lose their energy by the emission of a photon. It has been found experimentally by others that the efficiency for excitation of the luminescent atoms is largest close to the cathodic interface. By comparing transient measurements with the steady state situation we show that in steady state the efficiency is reduced and the difference between cathodic and anodic efficiency is larger. Both phenomena could be ascribed to creation of positive space charge during the first current pulses. ©1995 American Institute of Physics.