Lights Are Electric Circuits
Regardless of their additional functions, lights are essentially a simple electrical circuit. When exposed to a power source, electricity flows from the power source through a length of wire, through the light bulb, and back to the electrical ground. As current flows through the light bulb, it traverses a special section of wire known as a filament; the filament is resistant to electrical flow, and the resistance to the electrical current causes it to both glow and produce heat. Depending on the type of light and its application, the flow of electricity may be controlled with an electrical switch capable of breaking the circuit to interrupt the flow of electricity; when the circuit is broken and electricity stops, the light bulb no longer illuminates.
To make lights blink, manufacturers use a special type of filament known as a bimetallic strip. Like normal filaments, bimetallic strips are resistant to electricity and glow as electricity passes through them. As the strips heat up, however, they tend to bend, breaking the electrical circuit and causing the light to extinguish. After the strip breaks the circuit and stops the flow of electricity, it quickly cools down and springs back into its original shape, once again completing the flow of electricity. This on and off action of the light gives it a blinking effect, and the speed of the flashing can be adjusted through the use of different types of bimetallic strips.
Blinkers Can Control Lights
The same bimetallic strips that cause a single light bulb to flash on and off can also be used to control a series of lights. One of the most easily recognizable applications of bimetallic strips is in a string of lights used around the holiday season, sometimes referred to as "Christmas lights." In these lights, a special bulb with a bimetallic strip breaks the flow of electricity not only to itself, but to the entire string of lights; as the strip cools, the circuit is restored and the lights re-illuminate. This same application takes place in other blinking or flashing lights, where a special device known as a "relay" contains a bimetallic strip; when the relay heats up and the strip bends, the light---which may be an automotive light, or even a strobe on an airplane---flashes off, then back on.
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