Why traffic signals are precisely red, yellow and green

Traffic lights did not immediately become what we used to see them. Back at the end of the 19th century, quite dangerous devices appeared that even exploded, which is why they were quickly banned. But the number of cars grew every year, and a device that regulates the order of movement on the streets of large cities was simply necessary. Therefore, engineers and inventors continued to work on the creation of new mechanisms, and at the beginning of the last century, traffic lights appeared in the USA that were very similar to modern ones.

Like modern traffic lights, the American versions had a red signal prohibiting movement, and green, which meant permission to travel or pass. Later, a yellow signal was added to them, and in this form, traffic lights began to appear in the most advanced capitals of Europe.

But not in all countries green meant the possibility of movement. For example, in Japan they decided to use blue instead of green. In this form, traffic lights have existed in this country for 5 years. But after that, blue had to be abandoned in favor of green. Why did it happen?

It turns out that not all signals are equally well visible at a distance, and the degree of scattering depends on the wavelength: the longer the wavelength, the worse the light scatters when passing through the atmosphere. For example, blue is less visible than green because its wavelength is shorter and it dissipates faster in air. For this reason, it was decided to abandon him in Japan. And the red signal is best seen, because it is this color that has the longest wavelength, which guarantees maximum visibility even in fog or rain. If you pay attention to the color of the signals installed on the cars, you will notice that here the engineers use exclusively red and orange options, all for the same reason - they are best seen.