Q. Red colour is used for danger signals because

 2335  181 J & K CETJ & K CET 2007Ray Optics and Optical Instruments Report Error

Solution:

Red light is used in danger signals so that the danger signals can be seen distinctly upto large distances. The light used in the danger signals should not get scattered much, while passing through the atmosphere. Since, the red colour is scattered through a small amount due to its longer wavelength, the danger signals make use of red light.