Dimmer doubling uses the ability of a SCR dimmer to separately control the top and bottom halves of the voltage waveform. A dimmer doubler uses a high power diode arrangement to split the output of the dimmer into two halves, controlling two separate channels. This allows a single power cable to control two lights, but special 77V lamps must be used.
ETC's Source Four fixtures have a keying pin arrangement to prevent 77V lamps being accidentally inserted into 110V or 230V fixtures. Dimmer Doubled circuits typically use NEMA L5-15P connectors to differentiate them from 110V stage circuits.
Dimmer doubling is only supported on US (110V 60Hz) power types.