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All of us have learned since secondary school that the reason we use red in the traffic lights for "Stop" is because it travels the furthest without dispersion. According to wikipedia which cites, the first red-green traffic light was installed in 1912. Now, Dr. Maxwell discovered his three laws between 1861 and 1862. My googling threw up this link (which does not cite sources) that the red-green for stop-go was already standard practice in industrial controls by the 19th/20th century, which probably explains why and how Lester Wire came up with the red/green for his first traffic light installation.

So, was the choice of red-green for traffic lights industrial controls just a happy coincidence or did someone research them before coming up with the colors? If so (with research), why not have red and blue for traffic lights?

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I never learnt that in Secondary school... – MyUserIsThis Jan 30 '13 at 19:09
up vote 1 down vote accepted

Unfortunately, as cool as it would have been, it probably wasn't selected for that reason. Red is a natural color of danger, which is why many poisonous animals are red in color, while green is seen as more of a natural, peaceful color (Think nature, grass, trees..)

Potts design chose colors that are psychologically associated with the message they are meant to transmit. Red is classically seen as a color representing danger or caution. (There are countless phrases and idioms that use “red” as a message of the bad or unknown — “in the red,” “seeing red,” and “red herring,” among others.) Green, on the other hand, is a reassuring color in most cultures — the color of nature and growth; of harmony, freshness, and fertility. Green has a strong emotional correspondence with the idea of safety, and was intuitively chosen to guide pedestrians responsibly through an intersection.

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That is nonsense. Dangerous, poisoning rotten meat becomes green. Verdigris, the very common substance covering Miss Liberty and all bronze monuments, is a classic poison the romans used, and it is green. The cheeks of my peacefully sleeping doughter turn nearly red. Red are many flowers... Dangerous poison snakes and lizards are green. Wasps are black/yellow but not red... – Eduardo Guerras Valera Jan 30 '13 at 22:50
... Should I go on? Kissing lips are red. Sweet strawberries and delicious tomatoes are red. The most beautiful sunsets are red. Dark green is the color of stormy sea that fishermen have feared for centuries. Someone who lacks experience is said to be green. If you are jelous of someone, you are said to be 'green with envy', at least in Britain. Friendly, harmless parrots come in nearly every colour, including red... – Eduardo Guerras Valera Jan 31 '13 at 10:25
"A new study suggests the color red can serve as a danger signal to our unconscious minds, making people more likely to take actions that enhance their safety." I never said there aren't things that are safe and red. – DarkLightA Jan 31 '13 at 19:28

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