Experimental data show that in laboratory sparks, X-rays are produced in time synchronization with the meeting of streamers of opposite polarity just before the final breakdown of the discharge gap. It has been suggested that the electric field enhancement created during the collision of streamers could provide the necessary conditions for electron acceleration, even though some of the theoretical studies show that the duration of the electric field is not long enough to do so. The experimental data on laboratory discharges show that. when streamers of opposite polarity meet each other, a potential or ionization wave that renders the streamer channels conducting is initiated. This paper shows that these ionization waves that convert the discharge channels from weakly conducting to highly conducting are associated with electric fields large enough to accelerate electrons to relativistic energies.