Who decided that red means stop and green means go? Is there an underlying science to the color scheme?
I heard (how’s that for non-scientific!) that red light is easier to see at night and since you’re more likely to want people to know when to stop, they made the 'stop’light red. No sources to back this up though!
Carpe Diem!
I think red is easier to see in general. It commands attention better than other colors. Of course that still doesn’t really answer the question. 
Red is also the color of fire, and thus a natural signal of danger, whereas green is the color of foliage, and thus a natural signal of safety. Also except for red-green colorblind people, red and green are probably the easiest pair of colors to distinguish.
John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams
Half of this question is easy. Red is the color of blood, and thus is associated with danger and all sorts of other bad stuff. From what I’ve heard, green (and yellow) were pretty much pulled out of a hat. Traffic light colors are based on railroad semifore signals, BTW.
“I had a feeling that in Hell there would be mushrooms.” -The Secret of Monkey Island
Red is also the color of blood, making it more of a warning.
The red/green lights came from the railroads originally. A red light meant the track was blocked and the train should stop. A white (clear) light meant the track was, well, clear.
Somewhere along the line, the red lens cover fell off a signal. A train, seeing a white light and thinking the track was clear ran into a second train. The railroads started using green to indicate a clear track.
Red and green are chosen since they contrast well. Notice that navigation lights on ships and aircraft are also red and green.
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Dennis Matheson — tanstaafl@earthlink.net
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Well, I don’t think our traffic lights are derived from the railroad. As with many things in our culture, they owe their origins to nautical rules. A ship, sailboat, or whatever are required (in addition to others) to diplay a red light on the port side and a green light on the starboard side (that’s left and right respectively looking from the stern to the bow). Both International and Inland Rules state that when two vessels are crossing so as to involve risk of collision, the vessel which has the other on her starboard side (the give-way vessel) must keep out of the way and, if circumstances permit, cross behind the other vessel (the stand-on vessel). One way to remember this is that at night the give-way vessel will see the red (means danger) side light of the stand-on vessel and therefore must take action to pass astern. If you see a green side light, green means go, and you should maintain course and speed as the stand-on vessel. Also two vessels approaching each other head on, must keep to the right of each other; which explains why we (in America) drive on the right hand side of the road. Why the brits do it differently is beyond me.
“If you stick your finger in a pie, whatever is in the pie will be on your finger, and whatever is on your finger will be in the pie… unless you wear a rubber glove”----some demented old lady
Sheeeeeeesh. I wish you guys would take a browse through the Archives before wasting space on questions that Cecil has already answered…
Actually, red is relatively hard to see, especially at night. Your eyes respond much better to green/yellow wavelengths than to red wavelengths. Ever notice how newer fire engines are painted an ugly greenish-yellow color rather than the traditional red? That’s because someone finally realized that those bright red fire engines looked like bright BLACK fire engines after dark. The ugly yellow color maximizes visability in poor lighting conditions.
“For what a man had rather were true, he more readily believes” - Francis Bacon
Who cares what the colors are as long as they are in the right order?
Oh wait, now that is going to bring on a discussion of why red is on the top.
Ok. Ok. My fault. I searched for “red light”. Nowhere in Cecil’s column were those two words juxtaposed.
“Hard to see at night” isn’t a factor in a red light. Red objects to be seen by ambient light are a completely different issue.
John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams
I was responding to the assertion that the color red was chosen because it is easier to see relative to other colors. This isn’t true. Red light is relatively hard to see, regardless of whether it is emitted from a bulb, or reflected from a red object. Take a red light bulb and a yellow light bulb, each with the same luminosity, and move them further and further away from an observer - at some point the red light will be impossible to see while the yellow light remains visible.
Yes, traffic lights are generally bright enough that visibility isn’t really an issue. But it’s more correct to say that red light “commands attention” than that red light is “easier to see”.
“For what a man had rather were true, he more readily believes” - Francis Bacon