Question

Why is red colour used as a sign of danger?

Answer 1

Hint:Red light has the longest wavelength among all the colours in the visible spectrum whereas violet light has the shortest.

Complete step by step solution:
Earth’s atmosphere is composed of various gases which are collectively called air. So, when light passes through the atmosphere, it interacts with air molecules and subsequently gets scattered (Hence, we see the sky as primarily blue, since blue and violet light gets scattered the most owing to their short wavelength).

Now, we know that the amount of scattering of light is inversely proportional to the wavelength of light. Since the red light has the longest wavelength among all the colours in the visible spectrum, red light is scattered the least. Due to this, red light can travel longer distances as compared to other colours in the visible spectrum. So red light is visible from further distances.

Mathematically we can state the relationship between scattering and wavelength as follows:

\[Scattering{\text{ }}\alpha {\text{ }}\dfrac{1}{{{{\left( {Wavelength} \right)}^4}}}\]

Since we need to aware the maximum people when there is danger lurking around, so we use red light as a sign of danger (as most of the people can clearly see it).


Note:We could argue that infrared waves have a longer wavelength than red but the issue with infrared is that we humans cannot perceive or detect infrared light. Hence, if we used infrared light as a danger symbol, everyone would need to carry an infrared detector in order to see it.