Local laser ablation of the cathode of OLEDs has been applied to create a population of pinholes of the same size. This enables the direct comparison at different conditions of black spots and grey spots in the emission of OLEDs as a result of water ingress into the device. We confirmed earlier observations on the operational effect of black spot growth as determined in a sequential test on particle induced pinholes. Furthermore, we measured the operational effect in parallel, providing data that are test independent. With the same population of pinholes we studied the operational effect of grey spot growth. The observed larger operational effect of grey spot growth with respect to that of black spot growth is attributed to a lateral flow of protons to the centre of the black spot. In this part of the black spot a depletion region is present which is created by transport of H3O+ to the cathode under the influence of the applied electric field. This proposal is supported by the observation of black and grey spot growth in polymer LEDs on basis of PEDOT:PSS with increased pH.