Why are Traffic Lights Red, Amber, and Green

Nov 27, 2022 News

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Kaieteur News – Have you ever wondered just how the colours for traffic signals were chosen? Why red, amber and green? Surely, with all the colours in the world, traffic lights could have been any colour, but they are red, amber, and green. Well it turns out that there is a perfectly good explanation for the colours used in traffic signals.

The conventional idea that red means stop and green means go affects more than just traffic light colours. It is a perception that is shared by most people in the world. We have been taught from an early age that red means danger while green means safety. But why were those particular colors chosen for traffic lights in the first place? For something we have to look at every day, why couldn’t prettier colors be chosen, like magenta or turquoise; or pink and purple? Well, you’re about to find out.

To begin this story, we must examine the history of traffic lights as we know them.

According to a Washington State University magazine, the first gas-lit traffic lights were installed outside the Houses of Parliament in London, on December 10 1868. Proposed by British railway engineer, J.P. Knight, to control the traffic of horse carriages, gas lights were manually controlled by a Police Officer using semaphore arms. At night, gas-lit red and green lights were used, but they were still changed by a Police Officer. However, the lights became a safety hazard as they sometimes exploded and injured Police Officers.

Over the years, traffic lights evolved from being gas powered to electric powered.

It was an American in the early 1920s that revolutionised the traffic lights making them more effective and safe. Garret Morgan, after witnessing a terrible accident between a car and horse-drawn carriage, devised a T-shaped light that integrated the first ‘middle’ position — the color yellow — to denote the light was about to change. According to history.com, on November 20, 1923, the U.S. Patent Office granted Patent No. 1,475,074 to 46-year-old African American Inventor and Newspaperman Garrett Morgan for his three-position traffic signal. Though Morgan’s was not the first traffic signal (the first being installed in London in 1868), it was an important innovation nonetheless: By having a third position besides just ‘Stop’ and ‘Go’, it regulated crossing vehicles more safely than earlier signals had.

What is the history behind the colors?

It’s important to know that before there were traffic lights for cars, there were traffic signals for trains. At first, railroad companies used red to mean stop, white to mean go and green to mean caution.

Some Train Conductors ran into a few problems with the colour white meaning go—bright white could easily be mistaken for stars at night, with Train Conductors thinking they were all clear when they really weren’t. Railway companies eventually moved to the color green for go. And because it is easily distinguishable from the other colors, yellow became the standard for indicating when trains should proceed with caution. It’s been that way ever since.

When traffic lights were put up, it became standard for them as well—except in Japan, where you’ll find an entirely different color that signals go. And this is so because hundreds of years ago, the Japanese language included words for only four basic colors: black, white, red, and blue. If you wanted to describe something green, you would have to use the word for blue which is ‘ao’ and that system worked well enough until roughly the end of the first millennium, when the word ‘midori’ (originally meaning ‘sprout’) began showing up in writing to describe what we know as green.

Initially, Japan’s traffic lights were green as green can be. Despite this, the country’s official traffic documents still referred to green traffic lights as ‘ao’ rather than ‘midori’. While international traffic law decrees all ‘go’ signals must be represented by green lights, Japanese linguists objected to their Government’s decision to continue using the word ‘ao’ to describe what was clearly ‘midori’. The government decided to compromise. “In 1973, the Government mandated through a cabinet order that traffic lights use the bluest shade of green possible—still technically green, but noticeably blue enough to justifiably continue using the ‘ao’ nomenclature,” said Allan Richarz  who writes for Atlas Obscura.

Why was red chosen for stop?           

Scientifically, it has been proven that red light is the color with the longest wavelength. This factor means that as it travels through air molecules, it gets diffused less than other colors, so it can be seen from a greater distance. For a real-world example, think about how the light turns red as the sun sets. Even though the human eye is most sensitive to a yellow-green highlighter color (hence the shade of high-visibility safety vests), it can see red from further away.

Yellow light has a shorter wave length than red but a longer wavelength than green. This means that red is visible the furthest away, yellow in the middle and green the least distance away—a helpful advanced warning for needing to slow or stop. But this information could be a coincidence. Red meaning stop originated with train warning lights as mentioned earlier, and it is not clear whether that colour was chosen based on wave length, contrast against green nature or natural association of red with things like blood. It could be a combination of all three!

Believe it or not, yellow was once used to mean stop, at least as far as signage goes. Back in the 1900s, some stop signs were yellow because it was too hard to see a red sign in a poorly lit area. Eventually, highly reflective materials were developed, and red stop signs were born. Since yellow can be seen well at all times of the day, school zones, some traffic signs and school buses continue to be painted in that color.

And there you have it; the historical reason traffic signals use the colours red, amber/yellow and green.

The signal mentioned earlier that Morgan patented was a T-shaped pole with three settings. At night, when traffic was light, it could be set at half-mast (like a blinking yellow light today), warning drivers to proceed carefully through the intersection.

Morgan eventually sold the rights to his invention to General Electric (GE) for US$40,000.

 

 

 

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