As a result, gas discharge lamps cannot be directly connected to a voltage source. Certain impedance must be placed between the discharge lamp and the voltage source as a means to limit lamp current. For example, Figure 3(b) shows the effect of series resistance in stabilizing lamp current. The dotted lines VLa and VR show the voltage potential across the discharge and resistor, respectively, and the solid line VAB shows the potential across the pair in series.