 A silicon-controlled rectifier, or SCR, is a specialized type of control diode. The electron flow is the same as in an ordinary diode, from cathode to anode. However, unlike other diodes which only perform an on-and-off function, a SCR can regulate a flow of electricity with gradation when forward-biased. This is accomplished by manipulation of the adjustable gate control. This gate control function determines when and how much the SCR conducts. A common application of SCRs is in light bulb dimmers. Here is a circuit that contains a light bulb and a SCR. As the switch at the gate controller is adjusted to control power in the AC circuit, note the timing of the gate pulse and the subsequent change in the waveforms. Also, observe that average current flow increases and the light bulb becomes brighter.