We have studied the device degradation of single layer poly(2,5-dialkoxy-p-phenylenevinylene) light emitting diodes by electroabsorption spectroscopy. The applied direct current (dc) bias generates an opposing internal field. This internal field rises as the applied dc bias is increased. The development of the internal field is less pronounced in vacuum than in an ambient atmosphere and is no longer apparent for devices that were prepared and tested under an inert atmosphere in a glovebox. For the devices that were tested in air and under dynamic vacuum conditions we have also observed a change in the flat band voltage of the devices due to an aging effect on the electrodes. The combination of these two processes leads to an increase in the device turn-on voltage with increasing operating time. © 1999 American Institute of Physics.