UPDATED 2015-12-11
Based on:
http://blog.thelifeofkenneth.com/2010/01/switching-120vac-with-5v-digital-logic.html
http://everycircuit.com/circuit/5366253166264320
For the circuit on the left, a microcontroller would normally take the place of the SPDT switch. Using a relay and transistor, the switch controls 120VAC lamps, while using very little power itself.
