Red light – a warning of danger
Cars that meet a red light must stop. When repairing roads, at night, the repair places must turn on the red lights. The red light is also used as a signal light on the safety doors, on high towers, etc.
Why must you turn on the red light? The red light is the brightest and the most beautiful. Right, there is also an important optical principle here!
In white light, we know that there are seven types of colored light: red, orange, yellow, green, blue, indigo, and purple. With different color light, the wavelength is also different. The longest wavelength of red light can penetrate tiny particles like raindrops, dust particles, mist particles, etc. The shortest wavelength of purple light, the penetrating power is also relatively small. When light hits tiny particles, scattering occurs, that is, deviating from the original step and scattering. Light has different wavelengths; the scattering situation is also different. Light has a relatively short wavelength, like purple, indigo, etc. are very easy to scatter out, less light can penetrate through the tiny particle. Red light has a relatively long wavelength that is difficult to scatter; many rays penetrate tiny particles. So, in foggy weather, we see that the Sun is red. Standing behind the dim glass, seeing the light, it was red.
Because red light is not easily scattered, has a very strong penetrating ability, it is widely used as a warning signal of danger. Even the bicycle tail light is red, letting the person behind you know there is a vehicle ahead, avoiding traffic incidents.