Why use red instead of other colors as the warning light color?

Problem description:

The spectrum and dispersion of light are related. Why should red be used as the color of the alarm lamp instead of other colors?

Analysis:

When the sky is clear in Wan Li, the sky looks blue. What is the reason? White light is actually a mixture of red, orange, yellow, green, blue, indigo and purple. When sunlight enters the atmosphere, the sky we see is blue, because "air molecules scatter blue light easily". At sunrise and sunset, because the light needs to pass through the thick atmosphere, more blue light is scattered, so more red light or yellow light remains, so the sky turns red at sunrise and sunset.

When light shines on tiny particles, the particles will absorb the energy of light, and part of this energy will become the internal energy of the particles, which is called absorption, and the other part will still be emitted in the form of light, which is called scattering. The scattering effect is related to the wavelength of incident light and the size of particles. If the particles are very small, "the shorter the wavelength of light, the easier it is to scatter." Among white light, blue light has a shorter wavelength, so Lao Wang's smoke is also blue, similar to the principle that the atmosphere scatters blue light.

When sunlight passes through the atmosphere, blue light is easy to scatter, that is to say, red light or light with longer wavelength is easy to pass through, so the warning light is mainly red light, which can clearly shoot the ground from high altitude by infrared rays without being affected by clouds.