In the holiday season, you will see strings of lights decorating homes, trees, and streets. Some of them blink or change color. They come in special configurations: icicles hanging from gutters, string nets covering bushes, snowflakes and candy canes twinkling away. When decorating is as simple as plugging in some lights, it is easy to see why they are so popular. But how do they work? There is some very interesting science behind these lights that make the season bright.
How to Light a Lightbulb
Older, incandescent string lights work on principles of electricity that have been known for years. You plug in the bulb and electricity flows through a circuit. In the lightbulb, the electricity travels through a filament that produces light and heat. When the filament breaks, the circuit breaks. It is time to get a new lightbulb.
How to Light a String of Bulbs
A string of incandescent holiday bulbs works on the same principle. It is just a much longer circuit. Electricity travels from bulb to bulb, emitting heat and light along the way. In older strings, when one filament breaks, the whole circuit is broken and no lights will light up.
To solve this problem, and help identify the broken bulb, designers added an extra wire known as a shunt wire. This wire, which is placed beneath the filament, is specially coated so that it cannot conduct electricity while the filament is burning. The heat of the filament burnout melts this coating. Then the electricity can flow through the shunt wire, continuing the circuit. For the decorator, this means that a single light will be out on the string, making it much easier to replace the burnt out bulb.
What About Those Flashing Lights?
For incandescent bulbs, the easiest way to make them flash is by adding a special blinker bulb to the string. This bulb has yet another strip of metal cleverly designed to bend and straighten at different temperatures. Remember that the bulb emits light and heat. When the strip is warmed by the heat of the bulb, it bends back, breaking the circuit and turning off all the lights on the string. When it cools, it straightens, reconnecting the circuit and turning the lights back on. This cycle will continue as long as there is power to the circuit.
The LED Innovation: Light Without Heat
Explaining how a string of holiday lights works was much easier when it was just the incandescent bulbs. Today, most new strings of lights use LED, or light-emitting diode, bulbs. When you are looking at these lights, you are entering the world of subatomic particles. These bulbs emit photons when electrons move back and forth in a semiconducting material. Because there is no filament, they produce light without heat. They use much less electricity than regular bulbs. These strings can also be programmed to flash in different patterns, which will turn your holiday display into a winter light show.