Why Do All the Christmas Lights Go Out When Only One Bulb Blows?

Illustration for article titled Why Do All the Christmas Lights Go Out When Only One Bulb Blows?

If you've dabbled in Christmas decorations with traditional Christmas lights, you'll know that when one bulb blows, the entire line goes out with it. Why is that? Because of how the manufacturers wire them.

That image above shows how the lights and power supply are typically wired (not the new LED varieties, though) in traditional Christmas lights. If the filaments of all the bulbs are intact, then the circuit is complete and all the lights work. But if one bulb so happens to break then the entire circuit is broken, thus making all the lights go out. It's basically much cheaper for manufacturers to build lights like this because it allows them to use this cheaper series wiring with inexpensive bulbs.

If you're interested in finding the borked bolb and possibly salvaging the lights, you'll have to perform a binary chop. Those instructions can be found here. [JGC.org via MAKE]

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Modern string lights shouldn't go out.

They've been manufactured with a shunt built into the bulb, just below the filament.

When the filament burns out it burns the coating on the shunt which keeps the series circuit working.

But even with that safeguard there is still a drawback... If you remove the bulb (hence removing the shunt) the line will still go out.

The best way to avoid the whole mess is to get LED lights. They last WAY longer. :-p