Why Is It Red For Stop?
By Sue Clark on Feb 18, 2008 in The Light Side 
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I came across a site the other day that had an intriguing title: Why Can’t I Cook My Sister? It’s actually from a book, Father Knows Less Or: “Can I Cook My Sister?”: One Dad’s Quest to Answer His Son’s Most Baffling Questions
One of the questions submitted came from a 3 year old from Brooklyn, NY, who asked, “Why is it red for stop and green for go?” The answer to this question came from Carl Andersen, manager of the Federal Highway Administration’s Arens Photometric and Visibility Lab, Turner-Fairbank Highway Research Centre, McLean, Virginia. And I quote:
“Robert Louis Stevenson [the Scottish engineer and lighthouse builder] was looking for an alternative colour to white - most lighthouses had a white beacon - because he was building a lighthouse near to one that already existed, and he was afraid that ships wouldn’t be able to tell which lighthouse they were looking at. Of the light sources and coloured glass available at the time, he found that red was the next most intense light - it was the colour that would be seen from the greatest distance. So red was adopted in maritime signalling as an alternative to white lights, and was later adopted by the British Admiralty in 1852 for the port-side running light on steam vessels.
“A vessel observing that red light at night on another ship had to yield right-of-way to that ship. Green was adopted for the starboard-side running light: vessels seeing the green light on other ships had the right-of-way. When railroads were developed, engineers adopted this existing system as meaning stop and go. Then, as motor vehicles began to appear, engineers adopted railroad signalling. And in 1914, Cleveland installed the first red and green traffic control light. It had nothing to do with a perceived cultural reason. It just happened to be, with the technology at the time, the light sources at the time, and the glasses, that red provided the next best available light to white.”
It’s amazing what an impact lighthouses had (and still are having as anyone who’s sat at a traffic light can tell you) on our world.
The book is available at Amazon (affiliate link) if you’re interested in purchasing it.
Father Knows Less Or: “Can I Cook My Sister?”: One Dad’s Quest to Answer His Son’s Most Baffling Questions
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