Drivers across the globe are familiar with the red, yellow and green traffic lights that help guide movement along the roads. But do you know why these three became the chosen colours within the visible colour spectrum? The answer involves the history of transport, colour psychology , and basic physics.
The first three-way coloured traffic light was designed by Detroit police officer William Potts in the 1920s. He adapted the system for the road, and they were later standardised in the United States and many other countries across the globe.
The use of red was the perfect choice. But there is also physics involved. Red is present at one extreme of the visible spectrum, and has the longest wavelength within it. It dissipates less in the atmosphere and is visible from the farthest distance. It is even visible through fog and rain, as the colour refracts the least. Thus, the use of red to tell vehicles to stop and as a warning sign did not need any debate.
Because of its association with blood and fire, it is inherently connected with danger in the human mind, likely.
