The transient and steady state performance of organic light- emitting devices (OLEDs) has been investigated with a view towards suitability for pulse sources. The rise and fall times of the electroluminescence of the different structures and materials were afforded special attention. The tested devices cover single and multi-layer structures with different layer thicknesses. Both molecular and polymeric- based devices were tested. Molecular materials used in the OLEDs were N, N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD) as a hole transporter, tris-(8-hydroxyquinolate) aluminum (Alq3) as an electron transporter/emitter and 4,7-diphenyl-1,10-phenanthroline (BCP) as a hole blocking material. Poly)2-methoxy, 5-(2'-ethyl-hexoxy)-1,4- phenylene-vinylene) (MEH-PPV) and poly(3,4- ethylenedioxythiophene)/poly(styrene) (PEDOT/PSS) were the polymeric materials used in the devices. The effect of the driving voltage on the response time and the current density in transients was under investigation. In addition, changes in the response time were studied, when the bias voltage was applied.