Glossary

Light emitting diodes, commonly called LEDs, are real unsung heroes in the electronics world. They do dozens of different jobs and are found in all kinds of devices. Among other things, they form numbers on digital clocks, transmit information from remote controls (the red light at the tip of the TV remote), light up watches and tell you when your appliances are turned on. 
Basically, LEDs are just tiny light bulbs that fit easily into an electrical circuit. But unlike ordinary  bulbs, they don't have a filament that will burn out, and they don't get especially hot. They are illuminated solely by the movement of electrons in a semiconductor material, and they last just as long as a standard transistor. The lifespan of an LED surpasses the short life of an incandescent bulb by thousands of hours.