In recent decades LEDs (Light Emitting Diodes) have become widely used as indicators on all sorts of electrical equipment and more recently as replacements for traditional lights. Because they are solid they are not easily damaged; there is no delicate glass bulb or tube. They give out more light than ordinary lamps of the same power; in other words, they are more efficient. Because they do not get hot they are unlikely to cause fires.
The colour of an LED depends on what it is made from and not on the colour of its plastic case. The way in which LEDs work is too complex to explain here. It is however different from the other three types of light source: light from hot materials (incandescence), light from fluorescent materials and light from chemical reactions (other than burning). LEDs are beginning to replace low power lights such as indicator lights on motor cars, and may eventually replace most ordinary electric lights.