The idea that red means stop and green means go affects more than just traffic light colors. We have been taught from a young age that red means danger, while green means safety. For something we have to look at every day, why couldn't they have been prettier colors? You're about to find out.
Before there were traffic lights for cars, there were traffic signals for trains. At first, railroad companies used red to mean stop, white to mean go and green to mean caution. But train conductors ran into a problem with the color white meaning go—bright white could easily be mistaken for stars at night. It has been that way ever since.
That means that as it travels through the air, it gets diffused(分散) less than other colors, so it can be seen from a greater distance. For example, think about how the light turns red as the sun sets. Even though the human eye is most sensitive to a yellowish-green highlighter color, it can see red from further away. But this could happen by chance. It's not clear whether that was chosen based on wavelength, contrast against green nature or natural connection of red with things like blood.
Yellow has a shorter wavelength than red but a longer wavelength than green. This means that red is noticeable the furthest away, yellow in the middle and green the least distance away—a helpful advanced warning for needing to slow or stop.
However, believe it or not, yellow was once used to mean stop. Back in the 1900s, some stop signs were yellow because it was too hard to see a red sign in a poorly lit area. Since yellow can be seen well at all times of the day, school areas, some traffic signs and school buses continue to be painted the color. Keep these safe driving tips in the back of your mind whenever you see a yellow light.
A. Railway companies eventually moved to the color green for go.
B. It could be a mix of all three!
C. But why were those particular colors chosen for traffic lights?
D. Employ these driving rules and know that traffic lights have certainly come a long way.
E. Red is the color with the longest wavelength.
F. When you're impatiently waiting at a traffic light, don't get mad.
G. Eventually, highly reflective materials were developed, and red stop signs were born.
