If You See an Extra Red-Tipped Bulb On Your Christmas Lights, This Is What It’s For

Updated: Nov. 27, 2023

It turns out that the random red-tip Christmas light bulbs inside your Christmas light box isn't so random after all.

The holidays are officially here! Folks are lighting up every space of their homes, from colorful outdoor holiday lighting displays to cheerfully illuminated Christmas trees.

When digging into a new set of Christmas lights, it’s not unusual to find a random red-tipped lightbulb inside the box, wrapped in cellophane alongside a spare bulb. Often, the red-tipped lightbulb gets ignored or discarded, or people tend to think it’s meant for when a bulb goes out on a strand. But, the red-tipped lightbulb isn’t meant for Christmas tree light repair at all—it’s a blinker bulb!

How Do Blinker Bulbs Work?

According to Christmas Light Source, replacing one of your Christmas tree light bulbs with a red-tipped bulb will make the lights on that circuit flash and blink. Yep, the red-tipped Christmas light bulb is meant to make holiday lights blink, and twinkle if you will!

The way the bulb works to create twinkling Christmas magic is with an extra piece of metal at the top of the bulb called a bi-metallic strip. When the filament in the bulb gets hot from the light current, it bends this strip which causes the lights to go out. When the strip cools down, it straightens out, reconnects and relights the filament, meaning the light goes back on.

@kassidyyy__making christmas lights twinkle !! did you hear about this before ??🎄✨

♬ Christmas (Baby Please Come Home) – Darlene Love

Does It Matter Where You Place the Red-Tipped Bulb?

The number of Christmas tree lights on your strand will typically determine if the red-tipped lightbulb will make the entire strand of lights flash or just the lights in the circuit where the red-tipped lightbulb was placed. Keep that in mind when you swap out a clear or colored bulb for the red-tipped bulb when your Christmas lights are not working—the placement of the red-tipped bulb on light counts of 100 and up will determine where the lights blink on that stand.

According to Christmas Light Source, for most 50-count lights, a red-tipped Christmas lightbulb will cause the entire strand to blink. However, with 100-count lights or more, the lights only in the same circuit of the red-tipped bulb will flash.

How to Swap a Red-Tipped Lightbulb

Swapping a regular bulb with a red-tipped bulb is simple! First, pull one of the existing bulbs from the socket. Then pop the red-tipped bulb in its place. Keep in mind, though that lights of 100-plus have more than one circuit, meaning only lights in the section of the red-tipped light bulb will blink.

Should you decide that the blinking lights are not what you want this year, remember to tape the small plastic bag containing the red-tipped bulbs to the light strand when you store the Christmas lights in case you wish to use them next year.