Why red colour is used in traffic signals?

If we consider the VIBGYOR, then we can notice that red is at last, which means that the red colour has the highest wavelength. The main reason why the red colour is used to in the traffic signals to stop the vehicle is that red is scattered the least by the air molecules. For a particular colour, the scattering effect is inversely proportional to the power of wavelength. If th scattering increases, then its wavelength decrease. Since red is the most scattered light, it has the highest wavelength. Therefore, blue is scattered the most and red the least. Red has the highest wavelength of all the colours, and it is scattered the least. So, it can travel the longest distance and can penetrate through rain, mist and fog. This is the read for red being used in traffic signals so that the stop signal is visible from far as well. Also, red is perceived as and associated with danger. It has been genetically programmed that red is the colour of danger. These reasons also contribute to why red is used in traffic signals. read less