The present invention includes a smart controller for electroluminescent lamps which compensates for a range of RC time constants and adjusts its output frequency accordingly such that a relatively uniform light output is obtained on all illuminated areas of large EL display panels. The controller incorporates a device which monitors the current as the pulse train is applied to the EL panel. A sensing circuit determines if the current decayed to zero during the positive portion of the pulse. If the current did not decay to zero, the frequency is decreased until a decay to zero is sensed. Uniform light output is thus maintained from panel to panel, regardless of RC time constant differences between different EL panels, or variations in panel electrical characteristics over time. In an alternate embodiment of the present invention, several different frequencies are applied to the EL panel nearly simultaneously. In this case the frequency that effectively controls the light output is determined by the RC time constant of the EL panel circuit.