“When One Goes Out…They ALL Go Out!”

By Mark Phoenix posted November 29, 2021

Do you remember plugging in a string of Christmas lights to see if they worked?  With newer strings of Christmas lights, if there are any lights that burned out while they were stored away, you can simply replace the burned-out bulbs and the full string of lights would shine brightly.  Yet, it wasn’t always that easy...

With older strings of Christmas lights, if just one bulb burned out, the entire string of lights wouldn’t work.  Then, one by one, each bulb had to be unscrewed and a new bulb screwed in to determine if that was the “bad bulb” and light up the entire string again.  This can be a frustrating experience for the person who has the job of finding the “bad bulb”.  It often seemed that it was the last bulb in the string that was the “bad bulb”.

Did you ever wonder why it was with older strings of Christmas lights that when “One goes out, they ALL go out!”?  It seems the answer is somewhat simple.

I’m no electrician, yet here is the answer to the question:  Excluding new LED strings of Christmas lights, old style Christmas lights were wired in such a way that if the filaments of all the bulbs were intact, the electrical current would flow around the circuit.  If one bulb was broken or the filament was compromised, that breaks the circuit, and all the lights go out.

Newer strings of Christmas lights have a second piece of wire called a “shunt” that, even if one bulb is broken, the current would continue to flow to light the rest of the string of Christmas lights.  The burned-out bulb would need to be replaced, yet the rest of the string of lights remains lit.

For all the seeming frustration of the moment, looking back on years of putting up Christmas trees, replacing burned out light bulbs are just part of the fun at Christmas time.

Here's a couple more interesting items: 

• Are LED Christmas lights worth buying?  It seems so.  While more expensive to buy up-front, LED Christmas lights use 80% less energy to light and can last up to 25 times longer, according to most manufacturers.
• Even when your lights are turned off, they are still consuming energy.  It is called “Phantom Energy”.