With Christmas just hours away, odds are many of you have already been forced to hit the store for replacement lights for your tree. This is a fairly usual predicament during the holidays, as certain strands won’t work at all when one bulb goes out, while others remain lit regardless, with each bulb relying on its own circuit.

INSIDER had the chance to visit the factories where these holiday lights are made to learn about the intricacies and differences in lights by going behind the relatively complex production process. In short, it’s all in the manufacturing, and more specifically, how select strands are wired to produce the varying types of lights.

From wiring, to soldering, insulating, testing and twisting, press play above to see exactly how Christmas lights are made.

Up next, dive into the Highsnobiety guide to staying chill this holiday season.

Not NYC, not LA.

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