We learn so much from TikTok, and thanks to one user, we now know the function of those 'spare' red bulbs that are sometimes found in packs of string lights.
TikToker @viznelly took to the video-sharing platform to demonstrate exactly what they do - and our minds are blown.
You can watch the video below:
"I was today years old when I found out what these are for," they explained.
Moments later, they removed one of the regular bulbs from the string of lights that appeared to be turned off, and added in the red bulb instead.
"Wait for it," they added, before just seconds later, the lights change.
And people were mesmerised in the comments, with many struggling to understand how replacing the bulb could change the way the lights operate.
One person explained: "Old strings of lights come with an 'extra' light with a red tip. When you put it in for another bulb, it makes the whole string of lights blink."
While another added: "The old string lights ran at a constant power supply, by adding the red globe that is made different, the power cuts in and out."
And a third said: "As someone who grew up in the 90’s…I thought everyone knew this... We didn’t always have remote control lights!!"
Others were stunned that they never realised earlier, with one person commenting: "1000% thought they were spares. I have been robbed."
And another added: "I thought it was a tester to see what bulbs don’t work??"
Meanwhile a third said: "Dude all they had to do was write that somewhere on the box. I wasted so many years not knowing about this."
Others on the other hand were shocked that people didn't already know about the little red bulbs, with another person thinking it was 'common knowledge'.
"I used to put up the christmas lights at my parents house so i didn’t know that this wasn’t common knowledge," they said.
And another commented: "I known for years since i was a kid, im 33 now."
And a third added: "Thought everyone knew this. We called them blinkers!"
These days, many modern Christmas lights come with remote controls or switches on the plug sockets, but at least we know what these little red bulbs do in case we ever come across them.