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Greenlight Optics
Red Light, Green Light: How Traffic Lights Got Their Colors
Monday, April 13, 2015

While we may not dabble in the optic system that is our namesake, green lights are the quintessential symbol for “go” all over the world. Vertical, horizontal, single flashing red lights — all of these lights dictate traffic as well. While the construction may vary, the three colors remain consistent: red, yellow, and green. So why do these three colors rule the road? We dug a little deeper to find out just why a green light is a green light.

Before there were traffic lights, there were semaphores. And before cars were a primary method of transportation, there were trains. Semaphores were (and occasionally still are) used to signal to conductors whether it was safe to go or not on railways. A part of a signaling system, semaphores worked with different-colored flags and corresponding lamps in order to signal conductors. The color scheme that railways used is actually the basis for the traffic light: on the rails, there were red, white, green, blue, and black flags. While many rails today have phased out using this system, the colors some use today are red, white, yellow, and green.

The mid-1800s in England saw many accidents on the railways. Because of this, a standardized color system was put into place. The rails would now use red to indicate danger, white to indicate safety, and green to indicate “proceed with caution.” You read that correctly; it wasn’t everyone’s least favorite color of yellow that was given the cautionary job so many centuries ago. But after this standard became common practice, there seemed to be other problems that arose.

You see, the lamps used in the signaling system weren’t colored bulbs; they were simply white bulbs or even gas lamps during that era. To indicate danger or proceed with caution, a colored lens was placed in front of the light or lamp. But, those lenses could shift and fall out of place, leaving a white light blazing. Conductors would think that meant go, and would continue onward causing an accident. It is said this is when railways chose to adopt green for go and yellow to indicate caution, as there was a much greater contrast among the three colors.

Fast-forward a few years, and in 1868, the first non-electric traffic lights were installed at an intersection in London. That’s right, they were gas-lit traffic lights. Placed right outside of the British Houses of Parliament, these lights were installed because of the increase in horse-drawn carriages moving through the area, which made it difficult for pedestrians to cross the now-busy streets. Operated manually, this new light was similar to the semaphores used on railroads. This light used green for caution and red for carriages to stop.

It wasn’t until the 1900s, though, that an electric traffic light would be developed. The year was 1912, to be exact and, in 1914, a signal system with two colors and a buzzer was installed in Cleveland. Those two colors? Red and green. The buzzer was used to warn motorists of the color change. But before the three colors we came to know and loathe today were the norm, many places continued to use a two-colored semaphore signaling system, like youngins’ have seen in a Bugs Bunny or Road Runner cartoon. The third, and oftentimes most hated, color didn’t burst onto the traffic scene until 1920.

In Detroit, police officer William Potts was concerned about his fellow officers controlling signals at four different lights and that they could not change the lights at the same time. The solution? A third — technically a middle — light that would warn drivers the light was about to change to red. The new light was amber, and the idea to use this color came to Potts from none other than the railroad where they now used amber to indicate “proceed with caution.”

As an optical systems engineering company, we see various forms (and colors) of light on a daily basis. While we may not work on traffic lights in our line of work, the green light is our namesake. It doesn’t matter if they’re horizontal, vertical, acting as stop signs, or are sometimes even blue, traffic lights — among with many other optical systems — are in people’s everyday lives. Why these three specific colors dictate how fast you’re going to get to work in the morning is no longer a mystery; you can thank the folks who were working on the railroad, all the live-long day.


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