Question

why the colour red is used for danger signal please tell me

Answer 1

because as red colour has highest wavelength it can be seen from very far distance and it is considered as dangerous signals in places like turning it is you to ensure that driver that there is some dangerous signal and also let him know to go slow

Answer 2

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.