When do you go to Red and stop at Green? Ever wondered why traffic lights are coloured the way they are? You may probably say that Red represents danger. Green is for safety, and who cares for Yellow! What could be the real reason? Let's find out! Let's say we were to select the colours for traffic signals. What factors should we keep in mind? 

Our main focus should be the high visibility of colours, as this is extremely important for the drivers. It could be for a clear view from a distance or for visibility during extreme weather conditions. In such scenarios, the most important signal for us to be visible is STOP.

Why is Traffic Lights 🚥 Red, Yellow and Green ~ Tech Facts

So which colour should we choose for STOP?

Here's a spectrum chart of visible light. Which colours are most visible to you here? You'd probably say the ones in the middle, right? 

The human eye is most sensitive to green colour, followed by Yellow and Blue. So Green should be our STOP signal right? Not so fast! We also have to take the background into consideration here. During the day, the colours exhibited by our surroundings are mostly Green, Yellow, and Blue. So, Green would not contrast well with the background. 
Red is the colour that contrasts best with these colours. Also, there is another factor that comes into play here. When light travels a certain distance it gets scattered and we see a blurred image. Out of all the colours, Red scatters the least and Violet the most. So Red becomes a suitable choice for the STOP signal. Now, what about the other two signal lights? These are required when we are close enough to the traffic signal. And hence, the above-mentioned factors don't matter much. So we can use any two of Green, Yellow or Blue for the GO and CAUTION signal.

History of Traffic Lights

The first traffic lights were known as traffic lamp, which was small in size. Traffic 🚥  lights were invented by JP KNIGHT in 1868. He was an engineer for railway crossing signalling. The first traffic light was installed outside the parliament in London on 18th December 1868. But it was not even a month and it exploded. 

Why is Traffic Lights 🚥 Red, Yellow and Green ~ Tech Facts
Traffic Lamp


After this in the late 1890s, it had become very important to control traffic. Therefore, in 1910 Chicago developed an automatic traffic control system. When this system was installed in the railway system then 3 different colours were used.: RED, WHITE and GREEN. in which Red was for danger. Green meant for caution. And white was for going. But sometimes the lens of these lights fall off and white light was visible. Which made the driver think that the train can go forward and this made up in accidents. 
It was then decided that this light colour should be changed. So red was kept the same for danger. Green was made for 'go'. And white light was replaced by yellow(Amber) colour which denoted caution. 

Along with the Red, these two colours were selected and implemented by the railroads in the earlier 20th century. And afterwards, the same scheme was transferred for traffic signals.

 

Does traffic lights have yellow?

You might also be surprised to find out that the middle colour isn't Yellow, but it's Amber, a mix of Yellow and Orange. So this kind of explains the probable reason for choosing these colours. But is it always these three colours? Did you know that there are countries that have chosen Blue over Green as their GO signal? Why don't you try and find these countries' names and tell us in the comments section?

 

Why is one colour more visible to us than the other?

What do you think? Well, it depends majorly on our eyes. Why? The components of our eyes are similar to that of a camera. We know that depending on its hardware and software, the image we see differs from camera to camera. Similarly, how we see things in real life differs from person to person. 
For instance, one person may see a sight like this, while a Red and Green colourblind person will perceive the same sight like this. So the different components present in our eyes, determine the way we see things.

FAQ


1. Who invented traffic lights?

Traffic Lights was first invented by an engineer named JP Knight in 1868.

2. Where was first traffic light installed?

First traffic light was first installed in London, outside Parliament on 18th December 1868.