LEDs

stop light 

A light-emitting diode (LED) is a small light source that is illuminated by the movement of electrons through a semiconducting material. Families of semiconductors can be incorporated into devices that emit light over much of the visible spectrum upon electrical excitation. LEDs are increasingly used where low power consumption and long lifetimes are important. Some of the applications include: automotive break lights, advertising, and traffic signals. These light emitting diodes and diode lasers are revolutionizing many communication and display technologies.