Question

Why are danger signal lights red in colour?

Answer 1

The primary reason why the color red is used for danger signals is that red light is scattered the least by air molecules. The effect of scattering is inversely related to the fourth power of the wavelength of a color. Therefore blue which has the least wavelength of all the visible radiations is scattered the most and red which has the highest wavelength of all the colors we can see is scattered the least. So red light is able to travel the longest distance through fog, rain, and the alike.
Also, red is a color we inherently perceive as one that is associated with danger. I guess it has been genetically programmed as hot objects are red in color and also red is the color of blood. These reasons make danger signals the most effective when they are painted in red.