The tops of tall structures have red warning lights installed. These are easily seen from a distance because red light is the most visible of all colours.

Concept: Red light has the longest wavelength of any visible light, it is scattered the least by smoke fog.

Because of their shorter wavelengths, blue, yellow, and green light scatter more effectively.
The red is the least deviated, while the violet is the most.

Scattering of light is the phenomenon in which a light ray is redirected in all other directions after passing through particles with dimensions comparable to the wavelength of the light used. The danger signals installed on the tops of tall buildings are red because, of all colours, red is the least scattered by smoke or fog. This is primarily due to the fact that the wavelength of red is the longest. As a result, it is easily visible from a distance.