Series Lights

• Series lighting resembles a loop. A wire goes from one side of the wall socket to one side of the first bulb, and then from the other side to the next bulb and so on, and then back to the wall socket.
  
  

Parallel Lights

• In parallel lighting, the two wires from the wall socket connect to the two contacts on the first bulb. Then the same two wires extend on to the next bulb, and then the next continuing on to the last bulb.
  
  

Expansion

• Many parallel lights have a second outlet at the end of the string for extending with another lighting string. But you cannot extend or add on to series lights.
  
  

Burned-Out Bulbs

• One burned-out bulb in a parallel system will not affect the other bulbs. But in a series system, a burned-out bulb opens the circuit and shuts off all the lights.
  
  

Best Uses

• Since series lights make a loop, they may work better around the Christmas tree. Parallel lights may work better inside along a banister or outside along the eaves.
  
  

Precautions

• Both series and parallel Christmas lights may have small, harmless looking wiring. But they still carry 120 volts from the wall socket and can deliver a severe shock if not handled properly.