There are multiple hacks that we have learned later on in life that we wished we knew years and years ago. Many people share such hacks saying they were “today years old” when they learned it.

One recent hack we discovered when we were today years old has to do with Christmas lights. Seriously, you might want to sit down for this one if you’re not already sitting down.

Have you ever brought a box of Christmas lights that were all white and noticed a spare red Christmas light in the box? If you’re anything like us, you probably assumed that light was simply a spare so that you could easily replace a bulb if one burnt out. We always wondered why the spare bulb was red instead of white like the others, but we never thought about it too much, and we have thus far never needed to use it. Christmas string lights seem to last a surprisingly long amount of time.

One TikTok user was today years old when she discovered what the spare red light is really supposed to be used for. She demonstrated exactly what happens when you actually use this bulb.

First, she held up the red bulb to the camera so that we could easily see what it looked like. In the background, we see white Christmas lights around her garage door.

Then, she went over to the white lights and removed one of them. The lights went out, as Christmas lights do when one light isn’t working. That’s what the spare red light is for, right? Kind of, but not really.

Finally, she replaces the light she removed with the red light. The lights come back on, but that’s not all. Watch the video below to find out what really happens when you use the red Christmas light.

@viznelly **I** didn’t know. 🤩🎄☃️ #christmas #diy #home #homedecor #christmastiktok #christmasdecor #houseoftiktok #cleantok #housework #hometiktok #holiday #tips #hacks #hacksandtips #christmastree #navidad #feliznavidad ♬ It’s Beginning To Look A Lot Like Christmas – Bing Crosby

Wow, right? Many viewers were blown away by this hack and had no idea it was what the red light was for. One person wrote, “Dude all they had to do was write that somewhere on the box. I wasted so many years not knowing about this.”

Another viewer commented, “The blinky lights are nice but having one red bulb would bother me.”

Some viewers have known about this hack for a long time and shared that they “thought it was common knowledge.” Um, how? It’s not like it’s included in the directions anywhere. One person wrote, “As someone who grew up in the 90’s…I thought everyone knew this.”

Another comment reads, “Ppl saying ‘Omg I thought this was common knowledge’ as if it makes an oz of sense that putting a diff bulb in makes sht blink.”

Did you know the red bulb made the lights blink? Are you going to go pull the red bulb out of the box and make your Christmas lights blink?