The visible spectrum of light starts at red and moves to violet. Wavelengths of E.M. radiation slightly longer than red are infra-red and shorter than violet are ultra-violet, neither of which is visible to humans. My question is then: why do we see the spectrum of visible color as a cycle moving seamlessly from red to violet and through violet into red again (think of a color wheel)? Why do we not see the visible spectrum the way it would seem to make the most sense, i.e., fading in from invisible infra-red and fading out to invisible ultra-violet? This has been bugging me for some time now, hopefully one of the panelists here can give me a satisfactory answer or point me in the right direction.