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Why Are Traffic Lights Red and Green?

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Red and green images via Shutterstock

The very first traffic light, installed outside the Houses of Parliament in London in December 1868, had red and green gas lamps for nighttime use. The device was pretty crude, and less than a month after it went operational, it exploded and killed the unfortunate traffic cop who was operating it.

Obviously, we’ve come a long way in traffic light technology, but we’ve stuck with the same color scheme. What is it about red and green that gave them such lasting power?

The guys who made that first traffic light borrowed their palette from the railroads. British railwaymen of the time often used red, green, blue, black and white flags, semaphores and lamps for signaling. In January 1841, faced with Parliamentary investigation over a number of accidents, the major railroad managers met to discuss safety issues. Henry Booth of the Liverpool and Manchester Railway was a driving force at the meeting and recommended standardized hand signals and color schemes. The colors adopted were those used by Booth’s lines: red to indicate danger, white to indicate safety and green to indicate "proceed with caution."

Booth’s use of these colors, in turn, seems to have come from a common practice in heavy industry of the era. Many motors and other industrial equipment had indicator lights that were red when the equipment was stopped and green when it was running. Since people were already familiar with this color scheme and its meaning, it makes sense that it was handed down into the railroad industry and then to traffic lights.

As for why the early industrialists chose red to mean stop and green to mean go, we can only speculate. In color symbolism, red generally evokes danger and makes it a good choice for a warning signal. Green, on the other hand, is calming. While that doesn’t seem to lend itself well to “go,” it may have been chosen for a more practical reason - it contrasts well with red and is highly visible without being harsh or distracting.

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Big Questions
What Is the Difference Between Generic and Name Brand Ibuprofen?
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What is the difference between generic ibuprofen vs. name brands?

Yali Friedman:

I just published a paper that answers this question: Are Generic Drugs Less Safe than their Branded Equivalents?

Here’s the tl;dr version:

Generic drugs are versions of drugs made by companies other than the company which originally developed the drug.

To gain FDA approval, a generic drug must:

  • Contain the same active ingredients as the innovator drug (inactive ingredients may vary)
  • Be identical in strength, dosage form, and route of administration
  • Have the same use indications
  • Be bioequivalent
  • Meet the same batch requirements for identity, strength, purity, and quality
  • Be manufactured under the same strict standards of FDA's good manufacturing practice regulations required for innovator products

I hope you found this answer useful. Feel free to reach out at www.thinkbiotech.com. For more on generic drugs, you can see our resources and whitepapers at Pharmaceutical strategic guidance and whitepapers

This post originally appeared on Quora. Click here to view.

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Big Questions
Do Cats Fart?
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Certain philosophical questions can invade even the most disciplined of minds. Do aliens exist? Can a soul ever be measured? Do cats fart?

While the latter may not have weighed heavily on some of history’s great brains, it’s certainly no less deserving of an answer. And in contrast to existential queries, there’s a pretty definitive response: Yes, they do. We just don’t really hear it.

According to veterinarians who have realized their job sometimes involves answering inane questions about animals passing gas, cats have all the biological hardware necessary for a fart: a gastrointestinal system and an anus. When excess air builds up as a result of gulping breaths or gut bacteria, a pungent cloud will be released from their rear ends. Smell a kitten’s butt sometime and you’ll walk away convinced that cats fart.

The discretion, or lack of audible farts, is probably due to the fact that cats don’t gulp their food like dogs do, leading to less air accumulating in their digestive tract.

So, yes, cats do fart. But they do it with the same grace and stealth they use to approach everything else. Think about that the next time you blame the dog.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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