Christmas lights fill the landscape every December. Static and flashing, white and colored, they are ubiquitous. But what makes them light up and more importantly why do they all go off when a single bulb burns out? Learn everything you ever wanted to know about Christmas lights.
The lights most commonly used on Christmas trees today are known as mini-lights; they are 2.5 volt incandescent bulbs in multiples on strands. An incandescent bulb has a simple structure: a base with two metal contacts that connect to an electrical circuit on one side and two wires on the other, a thin filament that connects the two wires on the other side, and an inert gas, all inside a glass bulb. When the electrical circuit connected to the bulb is connected to a power supply, the current flows through the contacts, wire and filament; this movement of the current heats the atoms and gives off light.
An electrical outlet in the United States is generally 120-volt. Since the bulbs are each 2.5 volts, an outlet provides too much power for a single bulb. So, mini-lights were designed to connect serially in groups of 48 or 50. While 50 mini-lights uses slightly more than 120-volts, the dimming it causes to the strand is not really noticeable. When each bulb is in place, the circuit for the entire strand of lights is complete and the lights can glow. However, if a bulb is removed the serial circuit is broken and the lights will all be out. In the original mini-lights an entire strand would go out if a single bulb burned out, even if it was not removed. Many modern light sets have eliminated this problem by including a shunt. A shunt is an extra wire below the filament. After a filament burns out, the current can still flow through the shunt allowing the circuit to remain intact and the lights to stay on.
Many modern strands of Christmas lights are sold in groups of 100, 150, 200 and 300. Each of these is wired into individual groups of 50 lights, so that if you remove a bulb only one 50-bulb segment will go dark. In these instances, the separate groups of 50 bulbs are wired to operate in parallel to one another.
Many Christmas lights not only shine, they blink. Traditionally, the strands blink when a blinker bulb is added to the chain of lights. The blinker bulb contains a special piece of metal which bends when the filament heats. As the metal strip bends, it breaks the electrical current and the light goes out; as soon as it cools, the metal strip straightens out again and the bulb is relit; this process repeats continually causing the blinking effect.
Some modern light sets are more sophisticated; they contain electronic controllers to manage the blinking of the lights. These can be used to create different blinking patterns on the tree and are often called sequencers.
Bubble lights have a small amount of liquid in them, separated from the bulb. The liquid has a low boiling point and bubbles as soon as the bulb heats it up.
Christmas lights come in all colors and shapes today. Any color can be manufactured, simply by coloring the bulbs with translucent color; as the white light shines through the bulb, it glows with the bulb’s color.
