What makes a Traffic Light Work?

How traffic light systems work or what makes a traffic light work is a very simple but at the same time a complicated question. Actually, a traffic light works in several ways. It depends on the system put up. Fundamentally, you can find three major types of traffic signal lights. The old shaped timer dependent traffic lights, the coil wire dependent sensory traffic lights based on the theory of electromagnetism and the LED (light emitting diode) traffic lights. Whatever be the kind of system it is very interesting to know how it actually works and why only the colors Red, Green and Yellow act as indicators of traffic signals. These are the basic facts, which are very interesting and make up this article.