An analytic theory has been developed to calculate the rise of electroluminescence from bilayer light emitting diodes with internal energy barriers for bath majority and minority carriers upon applying a rectangular voltage pulse. Unless the mobility of the minority carriers-usually electrons, instead, is less than or equal to 2 x 10(-7) cm(2)/V s, onset of electroluminescence is governed by the growth of the interfacial charge densities and the concomitant redistribution of the electric field inside the device rather than by charge carrier transport. The crucial system parameters turn out to be the energy barriers that control hole and electron injection. Good agreement with experiment is found. (C) 1998 American Institute of Physics. [S0021-8979(98)08116-X].