Following is a transcript of the video.

Narrator: Have you ever wondered how these bands of lights come together? It's a simple string of miniature light bulbs, with some wiring inside that connects everything together.

Holiday light companies use various methods to make their string lights. Taizhou Haoran Machinery sells machines that create LED holiday light strings.

Here's how it works.

First, the wire is fed into the machine so it can be cut and shaped. Then, it is stripped at the tip and coated with flux, a cleaning agent that makes soldering and welding of metals a little easier.

Next in line are the LED light bulbs. They're fed into the machine and tested for positive or negative charges. Then, the metal ends of the lights are cut and shaped. Like the string, the LED light bulbs are also dipped in flux. The bulbs are then finally soldered with the wire.

The machine lines up all the stripped parts of the string with the individual light bulbs. The stripped ends of the string and the metal tips of the bulbs are soldered together. After the two parts are combined, each light is tested again for electric charge. Then the machine covers the metal piece in between the light bulb and the string with an insulator. The insulated lights are also wrapped with clear acrylic sleeves, to make them a little more durable. Lastly, the string is released and collected to go into the twisting machine.

And it comes out like this, bright and sparkling with colorful lights. Now, here's the thing.

The machine makes string lights in a series circuit. In a series circuit, the current passes from the power source to the first light, then the next, then the next, and so on, until it returns to the power source and completes the circuit. In this setup, if one bulb burns out in the strand, the current won't flow through the entire circuit, which means the entire string of Christmas lights will go out. Some of these could be replaced with a working bulb, but not all.

The other type of circuit light strands use is a parallel circuit. In this setup, each bulb is on its own circuit to the power source. The current is divided into paths, and since there is a separate path for each light, the rest of the bulbs will stay lit even if one goes out.

No matter what kind of lights the machine makes, they're finally ready to be hung up on a Christmas tree.

EDITOR'S NOTE: This video was originally published in December 2018.

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