The reason why red is on top of the spectrum of colours is because of the different wavelengths and frequency of the light. This is the asnwer:

Red is at the lower end of the spectrum and has a higher wavelength but lower frequency to that of Violet at the top end of the spectrum which has a lower wavelength and higher frequency.
taken from: http://www.colourtherapyhealing.com/colour/

What they're trying to say is that red vibrates lesser than violet (frequency) and that red has a longer wavelength than violet (wavelength). i'm sorry but i can't find a video for frequency and wavelength. Apologies! :)